Follow along with the video below to see how to install our site as a web app on your home screen.
Note: This feature may not be available in some browsers.
søndag den 7. maj 2023 kl. 01.16.17 UTC+2 skrev Phil Hobbs:
On 2023-05-06 16:55, John Larkin wrote:
On Sat, 6 May 2023 13:18:18 -0700 (PDT), Lasse Langwadt Christensen
lang...@fonz.dk> wrote:
lørdag den 6. maj 2023 kl. 21.52.56 UTC+2 skrev John Larkin:
On Sat, 6 May 2023 10:22:38 -0700 (PDT), Lasse Langwadt Christensen
lang...@fonz.dk> wrote:
lørdag den 6. maj 2023 kl. 17.56.04 UTC+2 skrev John Larkin:
On Sat, 6 May 2023 16:25:19 +0100, l...@poppyrecords.invalid.invalid
(Liz Tuddenham) wrote:
John Larkin <jla...@highlandSNIPMEtechnology.com> wrote:
Imagine a chassis with up to eight plugin boards. The chassis has a
pair of PWM controlled fans.
https://www.dropbox.com/s/8ubv5if7cbnsjzn/P940-8_front.jpg?raw=1
Each board will have a thermistor to sense board temperature. If any
board thinks it\'s too hot, it asks the fan controller to jog the fan
speeds up a notch. If nobody requests more air, the controller jogs
them down. That will work.
But I have a board with eight channels that can each get hot. There\'s
no place on the board that represents the worst-channel temperature. I
only have two available ADC channels so I can\'t use eight thermistors.
But thermistors are radically nonlinear. If I parallel four
thermistors into each ADC channel, the hottest of the four will
dominate. That should work well enough.
Some sort of diode thing might select the hottest thermistor, but
paralleling is easy.
Use 1N4148 (or equivalent) diodes in parallel and a constant feed of
1mA; the hottest one is the only one you are interested in and that one
will determine the voltage drop across the whole circuit. I did exactly
this with the thermal protection of a large amplifier where each output
transistor had its own heatsink.
That would behave similar to the parallel thermistors. The diode drops
would be about -2 mV per degree c and the current per diode would be
about 60 mV per decade. The result is a weighted temperature average.
Thanks for the suggestion. We have lots of single and dual
surface-mount diodes. Dual would double the signal.
maybe scan by grounding each diode in turn with an FPGA output?
Version 4
SHEET 1 920 820
WIRE 192 16 32 16
WIRE 464 16 272 16
WIRE 640 16 464 16
WIRE 848 16 640 16
WIRE 32 32 32 16
WIRE 272 48 272 16
WIRE 464 48 464 16
WIRE 640 48 640 16
WIRE 272 192 272 112
WIRE 464 192 464 112
WIRE 640 192 640 112
WIRE 272 304 272 272
WIRE 464 304 464 272
WIRE 464 304 272 304
WIRE 640 304 640 272
WIRE 640 304 464 304
FLAG 32 112 0
FLAG 272 304 0
FLAG 848 16 Vout
SYMBOL diode 256 48 R0
WINDOW 123 22 83 Left 2
SYMATTR InstName D1
SYMATTR Value 1N4148
SYMATTR Value2 temp={T}
SYMBOL res 176 32 R270
WINDOW 0 32 56 VTop 2
WINDOW 3 0 56 VBottom 2
SYMATTR InstName R1
SYMATTR Value 50k
SYMBOL voltage 32 16 R0
WINDOW 123 0 0 Left 0
WINDOW 39 0 0 Left 0
SYMATTR InstName V1
SYMATTR Value 3
SYMBOL diode 448 48 R0
SYMATTR InstName D3
SYMATTR Value 1N4148
SYMBOL voltage 272 176 R0
WINDOW 3 -5 161 VRight 2
WINDOW 123 0 0 Left 0
WINDOW 39 0 0 Left 0
SYMATTR InstName V2
SYMATTR Value PULSE(3 0 0 1u 1u 1m 3m)
SYMBOL diode 624 48 R0
SYMATTR InstName D2
SYMATTR Value 1N4148
SYMBOL voltage 464 176 R0
WINDOW 3 -5 161 VRight 2
WINDOW 123 0 0 Left 0
WINDOW 39 0 0 Left 0
SYMATTR InstName V3
SYMATTR Value PULSE(3 0 1m 1u 1u 1m 3m)
SYMBOL voltage 640 176 R0
WINDOW 3 -5 161 VRight 2
WINDOW 123 0 0 Left 0
WINDOW 39 0 0 Left 0
SYMATTR InstName V4
SYMATTR Value PULSE(3 0 2m 1u 1u 1m 3m)
TEXT -2 296 Left 2 !.tran 0 10m 1u
TEXT 208 -200 Left 2 !.step param T 25 100 5
LT Spice aborts that, \"unknown syntax\" error.
weird, I just tried it and it works here
https://imgur.com/a/ZKWEVur
Found it. There were three strange \"blank\" lines at the end of the
.asc that it didn\'t like.
That\'s sneaky, using the diodes as their own mux.
In the early \'90s, I built a diffraction-based sensor as an online
monitor for post-exposure bake in semiconductor lithography that worked
like that. It had seven 1 x 3 inch solar cells arranged in a cone (like
a poker hand, but 360 degrees).
All the cathodes were connected to a TIA together, and the anodes were
grounded one at a time, using a zero-power PAL with tri-state outputs.
(A PALCE22V10Z, iirc.) It had to be 3-state, because a logic high would
have forward-biased the solar cells. The photocurrent was pretty small,
so even a 1990 CMOS output resistance was negligible.
A normal PAL might not have worked, even in 3-state, because their low
output levels weren\'t that well controlled.
Lasse\'s suggestion is a bit different because the selected diode is
forward-biased, so a totem-pole output would be OK as long as it goes to
0V accurately enough.
Dunno about FPGAs--do their outputs really go to ground like that?
here\'s the plot of the Artix7 LVCMOS33 pull down from the ibis file (min/max/typ)
https://imgur.com/a/qFTQwNg
On Monday, May 8, 2023 at 1:50:12â¯AM UTC+10, Lasse Langwadt Christensen wrote:
søndag den 7. maj 2023 kl. 17.26.17 UTC+2 skrev Anthony William Sloman:
On Monday, May 8, 2023 at 12:22:13â¯AM UTC+10, John Larkin wrote:
On Sun, 7 May 2023 13:09:33 +0100, Martin Brown <\'\'\'newspam\'\'\'@nonad.co.uk> wrote:
On 06/05/2023 03:10, John Larkin wrote:
snip
Otherwise you will end up too sensitive to the channel with the lowest resistance at ambient temperature.
The thermistors are 2% resistance accuracy at 25c.
Cheap ones might be. Interchangeable thermistors do rather better.
I liked the Betathherm 0.2C interchangeable parts. That 0.8% accuracy.. Yellow Springs thermistors coukld do better, but they cost even more.
Diodes dV/dT in series might be more reproducible.
Or LM45s, but they have too many quirks.
https://www.ti.com/lit/ds/symlink/lm45.pdf?ts=1683472832545&ref_url=https%253A%252F%252Fwww.ti.com%252Fproduct%252FLM45
It\'s a 12 page data sheet (with eight extra pages for the package details). John Larkin seems to get quirked out easily.
he\'s just experienced and knows the datasheet rarely tells the whole story, afaict the LM45 is notorious for being prone to latchup, oscillation and generally finicky.
But he couldn\'t be bothered to spell out how it is quirky.
If you are posting here as an experienced person as bit more detail is expected, though perhaps not from John who is fishing for flattery rather than being helpful.
On Sun, 7 May 2023 08:00:22 -0700 (PDT), Lasse Langwadt Christensen
lang...@fonz.dk> wrote:
søndag den 7. maj 2023 kl. 01.16.17 UTC+2 skrev Phil Hobbs:
On 2023-05-06 16:55, John Larkin wrote:
On Sat, 6 May 2023 13:18:18 -0700 (PDT), Lasse Langwadt Christensen
lang...@fonz.dk> wrote:
lørdag den 6. maj 2023 kl. 21.52.56 UTC+2 skrev John Larkin:
On Sat, 6 May 2023 10:22:38 -0700 (PDT), Lasse Langwadt Christensen
lang...@fonz.dk> wrote:
lørdag den 6. maj 2023 kl. 17.56.04 UTC+2 skrev John Larkin:
On Sat, 6 May 2023 16:25:19 +0100, l...@poppyrecords.invalid.invalid
(Liz Tuddenham) wrote:
John Larkin <jla...@highlandSNIPMEtechnology.com> wrote:
Imagine a chassis with up to eight plugin boards. The chassis has a
pair of PWM controlled fans.
https://www.dropbox.com/s/8ubv5if7cbnsjzn/P940-8_front.jpg?raw=1
Each board will have a thermistor to sense board temperature. If any
board thinks it\'s too hot, it asks the fan controller to jog the fan
speeds up a notch. If nobody requests more air, the controller jogs
them down. That will work.
But I have a board with eight channels that can each get hot. There\'s
no place on the board that represents the worst-channel temperature. I
only have two available ADC channels so I can\'t use eight thermistors.
But thermistors are radically nonlinear. If I parallel four
thermistors into each ADC channel, the hottest of the four will
dominate. That should work well enough.
Some sort of diode thing might select the hottest thermistor, but
paralleling is easy.
Use 1N4148 (or equivalent) diodes in parallel and a constant feed of
1mA; the hottest one is the only one you are interested in and that one
will determine the voltage drop across the whole circuit. I did exactly
this with the thermal protection of a large amplifier where each output
transistor had its own heatsink.
That would behave similar to the parallel thermistors. The diode drops
would be about -2 mV per degree c and the current per diode would be
about 60 mV per decade. The result is a weighted temperature average.
Thanks for the suggestion. We have lots of single and dual
surface-mount diodes. Dual would double the signal.
maybe scan by grounding each diode in turn with an FPGA output?
Version 4
SHEET 1 920 820
WIRE 192 16 32 16
WIRE 464 16 272 16
WIRE 640 16 464 16
WIRE 848 16 640 16
WIRE 32 32 32 16
WIRE 272 48 272 16
WIRE 464 48 464 16
WIRE 640 48 640 16
WIRE 272 192 272 112
WIRE 464 192 464 112
WIRE 640 192 640 112
WIRE 272 304 272 272
WIRE 464 304 464 272
WIRE 464 304 272 304
WIRE 640 304 640 272
WIRE 640 304 464 304
FLAG 32 112 0
FLAG 272 304 0
FLAG 848 16 Vout
SYMBOL diode 256 48 R0
WINDOW 123 22 83 Left 2
SYMATTR InstName D1
SYMATTR Value 1N4148
SYMATTR Value2 temp={T}
SYMBOL res 176 32 R270
WINDOW 0 32 56 VTop 2
WINDOW 3 0 56 VBottom 2
SYMATTR InstName R1
SYMATTR Value 50k
SYMBOL voltage 32 16 R0
WINDOW 123 0 0 Left 0
WINDOW 39 0 0 Left 0
SYMATTR InstName V1
SYMATTR Value 3
SYMBOL diode 448 48 R0
SYMATTR InstName D3
SYMATTR Value 1N4148
SYMBOL voltage 272 176 R0
WINDOW 3 -5 161 VRight 2
WINDOW 123 0 0 Left 0
WINDOW 39 0 0 Left 0
SYMATTR InstName V2
SYMATTR Value PULSE(3 0 0 1u 1u 1m 3m)
SYMBOL diode 624 48 R0
SYMATTR InstName D2
SYMATTR Value 1N4148
SYMBOL voltage 464 176 R0
WINDOW 3 -5 161 VRight 2
WINDOW 123 0 0 Left 0
WINDOW 39 0 0 Left 0
SYMATTR InstName V3
SYMATTR Value PULSE(3 0 1m 1u 1u 1m 3m)
SYMBOL voltage 640 176 R0
WINDOW 3 -5 161 VRight 2
WINDOW 123 0 0 Left 0
WINDOW 39 0 0 Left 0
SYMATTR InstName V4
SYMATTR Value PULSE(3 0 2m 1u 1u 1m 3m)
TEXT -2 296 Left 2 !.tran 0 10m 1u
TEXT 208 -200 Left 2 !.step param T 25 100 5
LT Spice aborts that, \"unknown syntax\" error.
weird, I just tried it and it works here
https://imgur.com/a/ZKWEVur
Found it. There were three strange \"blank\" lines at the end of the
.asc that it didn\'t like.
That\'s sneaky, using the diodes as their own mux.
In the early \'90s, I built a diffraction-based sensor as an online
monitor for post-exposure bake in semiconductor lithography that worked
like that. It had seven 1 x 3 inch solar cells arranged in a cone (like
a poker hand, but 360 degrees).
All the cathodes were connected to a TIA together, and the anodes were
grounded one at a time, using a zero-power PAL with tri-state outputs.
(A PALCE22V10Z, iirc.) It had to be 3-state, because a logic high would
have forward-biased the solar cells. The photocurrent was pretty small,
so even a 1990 CMOS output resistance was negligible.
A normal PAL might not have worked, even in 3-state, because their low
output levels weren\'t that well controlled.
Lasse\'s suggestion is a bit different because the selected diode is
forward-biased, so a totem-pole output would be OK as long as it goes to
0V accurately enough.
Dunno about FPGAs--do their outputs really go to ground like that?
here\'s the plot of the Artix7 LVCMOS33 pull down from the ibis file (min/max/typ)
https://imgur.com/a/qFTQwNg
I wonder how real that is. The grounds around the chip aren\'t really
zero ohms to pcb ground.
søndag den 7. maj 2023 kl. 17.26.17 UTC+2 skrev Anthony William Sloman:
On Monday, May 8, 2023 at 12:22:13?AM UTC+10, John Larkin wrote:
On Sun, 7 May 2023 13:09:33 +0100, Martin Brown <\'\'\'newspam\'\'\'@nonad.co.uk> wrote:
On 06/05/2023 03:10, John Larkin wrote:
snip
Otherwise you will end up too sensitive to the channel with the lowest resistance at ambient temperature.
The thermistors are 2% resistance accuracy at 25c.
Cheap ones might be. Interchangeable thermistors do rather better.
I liked the Betathherm 0.2C interchangeable parts. That 0.8% accuracy. Yellow Springs thermistors coukld do better, but they cost even more.
Diodes dV/dT in series might be more reproducible.
Or LM45s, but they have too many quirks.
https://www.ti.com/lit/ds/symlink/lm45.pdf?ts=1683472832545&ref_url=https%253A%252F%252Fwww.ti.com%252Fproduct%252FLM45
It\'s a 12 page data sheet (with eight extra pages for the package details). John Larkin seems to get quirked out easily.
he\'s just experienced and knows the datasheet rarely tells the whole story, afaict the LM45 is notorious for being prone to latchup, oscillation and generally finicky
søndag den 7. maj 2023 kl. 17.26.17 UTC+2 skrev Anthony William Sloman:
On Monday, May 8, 2023 at 12:22:13?AM UTC+10, John Larkin wrote:
On Sun, 7 May 2023 13:09:33 +0100, Martin Brown <\'\'\'newspam\'\'\'@nonad.co.uk> wrote:
On 06/05/2023 03:10, John Larkin wrote:
snip
Otherwise you will end up too sensitive to the channel with the lowest resistance at ambient temperature.
The thermistors are 2% resistance accuracy at 25c.
Cheap ones might be. Interchangeable thermistors do rather better.
I liked the Betathherm 0.2C interchangeable parts. That 0.8% accuracy. Yellow Springs thermistors coukld do better, but they cost even more.
Diodes dV/dT in series might be more reproducible.
Or LM45s, but they have too many quirks.
https://www.ti.com/lit/ds/symlink/lm45.pdf?ts=1683472832545&ref_url=https%253A%252F%252Fwww.ti.com%252Fproduct%252FLM45
It\'s a 12 page data sheet (with eight extra pages for the package details). John Larkin seems to get quirked out easily.
he\'s just experienced and knows the datasheet rarely tells the whole story, afaict the LM45 is notorious for being prone to latchup, oscillation and generally finicky
søndag den 7. maj 2023 kl. 18.18.16 UTC+2 skrev Anthony William Sloman:
On Monday, May 8, 2023 at 1:50:12â¯AM UTC+10, Lasse Langwadt Christensen wrote:
søndag den 7. maj 2023 kl. 17.26.17 UTC+2 skrev Anthony William Sloman:
On Monday, May 8, 2023 at 12:22:13â¯AM UTC+10, John Larkin wrote:
On Sun, 7 May 2023 13:09:33 +0100, Martin Brown <\'\'\'newspam\'\'\'@nonad.co.uk> wrote:
On 06/05/2023 03:10, John Larkin wrote:
snip
Otherwise you will end up too sensitive to the channel with the lowest resistance at ambient temperature.
The thermistors are 2% resistance accuracy at 25c.
Cheap ones might be. Interchangeable thermistors do rather better.
I liked the Betathherm 0.2C interchangeable parts. That 0.8% accuracy. Yellow Springs thermistors coukld do better, but they cost even more.
Diodes dV/dT in series might be more reproducible.
Or LM45s, but they have too many quirks.
https://www.ti.com/lit/ds/symlink/lm45.pdf?ts=1683472832545&ref_url=https%253A%252F%252Fwww.ti.com%252Fproduct%252FLM45
It\'s a 12 page data sheet (with eight extra pages for the package details). John Larkin seems to get quirked out easily.
he\'s just experienced and knows the datasheet rarely tells the whole story, afaict the LM45 is notorious for being prone to latchup, oscillation and generally finicky.
But he couldn\'t be bothered to spell out how it is quirky.
If you are posting here as an experienced person as bit more detail is expected, though perhaps not from John who is fishing for flattery rather than being helpful.
Figures 16 and 17 in the data sheet make it clear that it is intolerant of capacitative loads. If you didn\'t read the data sheet this might come as a surprise.
Latchup isn\'t mentioned. If you can provoke the device into oscillation I suppose anything is possible. Getting the output above the supply rail can provoke all sort of odd behavior, and getting the output below the negative rail can inject charge carriers into the substrate, which can be even worse.
your snarky comments aren\'t helpful, what was your point?
søndag den 7. maj 2023 kl. 18.18.16 UTC+2 skrev Anthony William Sloman:
On Monday, May 8, 2023 at 1:50:12?AM UTC+10, Lasse Langwadt Christensen wrote:
søndag den 7. maj 2023 kl. 17.26.17 UTC+2 skrev Anthony William Sloman:
On Monday, May 8, 2023 at 12:22:13?AM UTC+10, John Larkin wrote:
On Sun, 7 May 2023 13:09:33 +0100, Martin Brown <\'\'\'newspam\'\'\'@nonad.co.uk> wrote:
On 06/05/2023 03:10, John Larkin wrote:
snip
Otherwise you will end up too sensitive to the channel with the lowest resistance at ambient temperature.
The thermistors are 2% resistance accuracy at 25c.
Cheap ones might be. Interchangeable thermistors do rather better.
I liked the Betathherm 0.2C interchangeable parts. That 0.8% accuracy. Yellow Springs thermistors coukld do better, but they cost even more.
Diodes dV/dT in series might be more reproducible.
Or LM45s, but they have too many quirks.
https://www.ti.com/lit/ds/symlink/lm45.pdf?ts=1683472832545&ref_url=https%253A%252F%252Fwww.ti.com%252Fproduct%252FLM45
It\'s a 12 page data sheet (with eight extra pages for the package details). John Larkin seems to get quirked out easily.
he\'s just experienced and knows the datasheet rarely tells the whole story, afaict the LM45 is notorious for being prone to latchup, oscillation and generally finicky.
But he couldn\'t be bothered to spell out how it is quirky.
If you are posting here as an experienced person as bit more detail is expected, though perhaps not from John who is fishing for flattery rather than being helpful.
your snarky comments aren\'t helpful, what was your point?
On Sun, 7 May 2023 08:50:07 -0700 (PDT), Lasse Langwadt Christensen
lang...@fonz.dk> wrote:
søndag den 7. maj 2023 kl. 17.26.17 UTC+2 skrev Anthony William Sloman:
On Monday, May 8, 2023 at 12:22:13?AM UTC+10, John Larkin wrote:
On Sun, 7 May 2023 13:09:33 +0100, Martin Brown <\'\'\'newspam\'\'\'@nonad..co.uk> wrote:
On 06/05/2023 03:10, John Larkin wrote:
snip
Otherwise you will end up too sensitive to the channel with the lowest resistance at ambient temperature.
The thermistors are 2% resistance accuracy at 25c.
Cheap ones might be. Interchangeable thermistors do rather better.
I liked the Betathherm 0.2C interchangeable parts. That 0.8% accuracy. Yellow Springs thermistors coukld do better, but they cost even more.
Diodes dV/dT in series might be more reproducible.
Or LM45s, but they have too many quirks.
https://www.ti.com/lit/ds/symlink/lm45.pdf?ts=1683472832545&ref_url=https%253A%252F%252Fwww.ti.com%252Fproduct%252FLM45
It\'s a 12 page data sheet (with eight extra pages for the package details). John Larkin seems to get quirked out easily.
he\'s just experienced and knows the datasheet rarely tells the whole story, afaict the LM45 is notorious for being prone to latchup, oscillation and generally finicky.
And nasty behavior from charge injection when connected to an ADC or a mux. It takes more parts to fix that.
NEVER run one from more than 5 volts.
On Sun, 7 May 2023 09:50:25 -0700 (PDT), Lasse Langwadt Christensen
lang...@fonz.dk> wrote:
søndag den 7. maj 2023 kl. 18.18.16 UTC+2 skrev Anthony William Sloman:
On Monday, May 8, 2023 at 1:50:12?AM UTC+10, Lasse Langwadt Christensen wrote:
søndag den 7. maj 2023 kl. 17.26.17 UTC+2 skrev Anthony William Sloman:
On Monday, May 8, 2023 at 12:22:13?AM UTC+10, John Larkin wrote:
On Sun, 7 May 2023 13:09:33 +0100, Martin Brown <\'\'\'newspam\'\'\'@nonad.co.uk> wrote:
On 06/05/2023 03:10, John Larkin wrote:
snip
Otherwise you will end up too sensitive to the channel with the lowest resistance at ambient temperature.
The thermistors are 2% resistance accuracy at 25c.
Cheap ones might be. Interchangeable thermistors do rather better.
I liked the Betathherm 0.2C interchangeable parts. That 0.8% accuracy. Yellow Springs thermistors coukld do better, but they cost even more.
Diodes dV/dT in series might be more reproducible.
Or LM45s, but they have too many quirks.
https://www.ti.com/lit/ds/symlink/lm45.pdf?ts=1683472832545&ref_url=https%253A%252F%252Fwww.ti.com%252Fproduct%252FLM45
It\'s a 12 page data sheet (with eight extra pages for the package details). John Larkin seems to get quirked out easily.
he\'s just experienced and knows the datasheet rarely tells the whole story, afaict the LM45 is notorious for being prone to latchup, oscillation and generally finicky.
But he couldn\'t be bothered to spell out how it is quirky.
If you are posting here as an experienced person as bit more detail is expected, though perhaps not from John who is fishing for flattery rather than being helpful.
your snarky comments aren\'t helpful, what was your point?
If anyone who actually designs electronics and wants to use an LM45 asks me about the quirks that we\'ve found, I\'d be happy to tell them.
On Sun, 7 May 2023 08:50:07 -0700 (PDT), Lasse Langwadt Christensen
lang...@fonz.dk> wrote:
søndag den 7. maj 2023 kl. 17.26.17 UTC+2 skrev Anthony William Sloman:
On Monday, May 8, 2023 at 12:22:13?AM UTC+10, John Larkin wrote:
On Sun, 7 May 2023 13:09:33 +0100, Martin Brown <\'\'\'newspam\'\'\'@nonad..co.uk> wrote:
On 06/05/2023 03:10, John Larkin wrote:
snip
Otherwise you will end up too sensitive to the channel with the lowest resistance at ambient temperature.
The thermistors are 2% resistance accuracy at 25c.
Cheap ones might be. Interchangeable thermistors do rather better.
I liked the Betathherm 0.2C interchangeable parts. That 0.8% accuracy. Yellow Springs thermistors coukld do better, but they cost even more.
Diodes dV/dT in series might be more reproducible.
Or LM45s, but they have too many quirks.
https://www.ti.com/lit/ds/symlink/lm45.pdf?ts=1683472832545&ref_url=https%253A%252F%252Fwww.ti.com%252Fproduct%252FLM45
It\'s a 12 page data sheet (with eight extra pages for the package details). John Larkin seems to get quirked out easily.
he\'s just experienced and knows the datasheet rarely tells the whole story, afaict the LM45 is notorious for being prone to latchup, oscillation and generally finicky.
I use LM45s. He doesn\'t.
Thermistors don\'t latch or oscillate!
On Monday, May 8, 2023 at 2:50:29â¯AM UTC+10, Lasse Langwadt Christensen wrote:
søndag den 7. maj 2023 kl. 18.18.16 UTC+2 skrev Anthony William Sloman:
On Monday, May 8, 2023 at 1:50:12â¯AM UTC+10, Lasse Langwadt Christensen wrote:
søndag den 7. maj 2023 kl. 17.26.17 UTC+2 skrev Anthony William Sloman:
On Monday, May 8, 2023 at 12:22:13â¯AM UTC+10, John Larkin wrote:
On Sun, 7 May 2023 13:09:33 +0100, Martin Brown <\'\'\'newspam\'\'\'@nonad.co.uk> wrote:
On 06/05/2023 03:10, John Larkin wrote:
snip
Otherwise you will end up too sensitive to the channel with the lowest resistance at ambient temperature.
The thermistors are 2% resistance accuracy at 25c.
Cheap ones might be. Interchangeable thermistors do rather better..
I liked the Betathherm 0.2C interchangeable parts. That 0.8% accuracy. Yellow Springs thermistors coukld do better, but they cost even more.
Diodes dV/dT in series might be more reproducible.
Or LM45s, but they have too many quirks.
https://www.ti.com/lit/ds/symlink/lm45.pdf?ts=1683472832545&ref_url=https%253A%252F%252Fwww.ti.com%252Fproduct%252FLM45
It\'s a 12 page data sheet (with eight extra pages for the package details). John Larkin seems to get quirked out easily.
he\'s just experienced and knows the datasheet rarely tells the whole story, afaict the LM45 is notorious for being prone to latchup, oscillation and generally finicky.
But he couldn\'t be bothered to spell out how it is quirky.
If you are posting here as an experienced person as bit more detail is expected, though perhaps not from John who is fishing for flattery rather than being helpful.
Restoring Lasse\'s snip
Figures 16 and 17 in the data sheet make it clear that it is intolerant of capacitative loads. If you didn\'t read the data sheet this might come as a surprise.
Latchup isn\'t mentioned. If you can provoke the device into oscillation I suppose anything is possible. Getting the output above the supply rail can provoke all sort of odd behavior, and getting the output below the negative rail can inject charge carriers into the substrate, which can be even worse.
your snarky comments aren\'t helpful, what was your point?
Since you snipped the point, and didn\'t mark the snip, your own comment is pretty snarky, and not exactly helpful. Your comment could be read as an admission that you had tried to use the LM45 without reading the data sheet, and hadn\'t worked out what you\'d done wrong before giving up on the device.
søndag den 7. maj 2023 kl. 19.18.45 UTC+2 skrev Anthony William Sloman:
On Monday, May 8, 2023 at 2:50:29â¯AM UTC+10, Lasse Langwadt Christensen wrote:
søndag den 7. maj 2023 kl. 18.18.16 UTC+2 skrev Anthony William Sloman:
On Monday, May 8, 2023 at 1:50:12â¯AM UTC+10, Lasse Langwadt Christensen wrote:
søndag den 7. maj 2023 kl. 17.26.17 UTC+2 skrev Anthony William Sloman:
On Monday, May 8, 2023 at 12:22:13â¯AM UTC+10, John Larkin wrote:
On Sun, 7 May 2023 13:09:33 +0100, Martin Brown <\'\'\'newspam\'\'\'@nonad.co.uk> wrote:
On 06/05/2023 03:10, John Larkin wrote:
snip
Otherwise you will end up too sensitive to the channel with the lowest resistance at ambient temperature.
The thermistors are 2% resistance accuracy at 25c.
Cheap ones might be. Interchangeable thermistors do rather better.
I liked the Betathherm 0.2C interchangeable parts. That 0.8% accuracy. Yellow Springs thermistors coukld do better, but they cost even more.
Diodes dV/dT in series might be more reproducible.
Or LM45s, but they have too many quirks.
https://www.ti.com/lit/ds/symlink/lm45.pdf?ts=1683472832545&ref_url=https%253A%252F%252Fwww.ti.com%252Fproduct%252FLM45
It\'s a 12 page data sheet (with eight extra pages for the package details). John Larkin seems to get quirked out easily.
he\'s just experienced and knows the datasheet rarely tells the whole story, afaict the LM45 is notorious for being prone to latchup, oscillation and generally finicky.
But he couldn\'t be bothered to spell out how it is quirky.
If you are posting here as an experienced person as bit more detail is expected, though perhaps not from John who is fishing for flattery rather than being helpful.
Restoring Lasse\'s snip
Figures 16 and 17 in the data sheet make it clear that it is intolerant of capacitative loads. If you didn\'t read the data sheet this might come as a surprise.
Latchup isn\'t mentioned. If you can provoke the device into oscillation I suppose anything is possible. Getting the output above the supply rail can provoke all sort of odd behavior, and getting the output below the negative rail can inject charge carriers into the substrate, which can be even worse.
your snarky comments aren\'t helpful, what was your point?
Since you snipped the point, and didn\'t mark the snip, your own comment is pretty snarky, and not exactly helpful. Your comment could be read as an admission that you had tried to use the LM45 without reading the data sheet, and hadn\'t worked out what you\'d done wrong before giving up on the device.
and your cranky post that you have never used it and think you know better than everyone else.
If it had proved to crankier than that I would have like to have learned how.
if you never used it and only read the data sheet how would you know?
On Monday, May 8, 2023 at 4:12:03â¯AM UTC+10, Lasse Langwadt Christensen wrote:
søndag den 7. maj 2023 kl. 19.18.45 UTC+2 skrev Anthony William Sloman:
On Monday, May 8, 2023 at 2:50:29â¯AM UTC+10, Lasse Langwadt Christensen wrote:
søndag den 7. maj 2023 kl. 18.18.16 UTC+2 skrev Anthony William Sloman:
On Monday, May 8, 2023 at 1:50:12â¯AM UTC+10, Lasse Langwadt Christensen wrote:
søndag den 7. maj 2023 kl. 17.26.17 UTC+2 skrev Anthony William Sloman:
On Monday, May 8, 2023 at 12:22:13â¯AM UTC+10, John Larkin wrote:
On Sun, 7 May 2023 13:09:33 +0100, Martin Brown <\'\'\'newspam\'\'\'@nonad.co.uk> wrote:
On 06/05/2023 03:10, John Larkin wrote:
snip
Otherwise you will end up too sensitive to the channel with the lowest resistance at ambient temperature.
The thermistors are 2% resistance accuracy at 25c.
Cheap ones might be. Interchangeable thermistors do rather better.
I liked the Betathherm 0.2C interchangeable parts. That 0.8% accuracy. Yellow Springs thermistors coukld do better, but they cost even more.
Diodes dV/dT in series might be more reproducible.
Or LM45s, but they have too many quirks.
https://www.ti.com/lit/ds/symlink/lm45.pdf?ts=1683472832545&ref_url=https%253A%252F%252Fwww.ti.com%252Fproduct%252FLM45
It\'s a 12 page data sheet (with eight extra pages for the package details). John Larkin seems to get quirked out easily.
he\'s just experienced and knows the datasheet rarely tells the whole story, afaict the LM45 is notorious for being prone to latchup, oscillation and generally finicky.
But he couldn\'t be bothered to spell out how it is quirky.
If you are posting here as an experienced person as bit more detail is expected, though perhaps not from John who is fishing for flattery rather than being helpful.
Restoring Lasse\'s snip
Figures 16 and 17 in the data sheet make it clear that it is intolerant of capacitative loads. If you didn\'t read the data sheet this might come as a surprise.
Latchup isn\'t mentioned. If you can provoke the device into oscillation I suppose anything is possible. Getting the output above the supply rail can provoke all sort of odd behavior, and getting the output below the negative rail can inject charge carriers into the substrate, which can be even worse.
your snarky comments aren\'t helpful, what was your point?
Since you snipped the point, and didn\'t mark the snip, your own comment is pretty snarky, and not exactly helpful. Your comment could be read as an admission that you had tried to use the LM45 without reading the data sheet, and hadn\'t worked out what you\'d done wrong before giving up on the device.
and your cranky post that you have never used it and think you know better than everyone else.
I certainly looked at using it from time to time, and I do get the impression that neither you nor John Larkin have looked at the data sheet all that carefully.
If it had proved to crankier than that I would have like to have learned how.
if you never used it and only read the data sheet how would you know?
It\'s called book knowledge and background information. You can find out quite a bit without going to the trouble of buying a few parts and playing with them, and this frequently lets you off some tine-consuming experimentation. Engineers do go in for that sort of thing. Tinkerers don\'t have the option.
søndag den 7. maj 2023 kl. 20.45.41 UTC+2 skrev Anthony William Sloman:
On Monday, May 8, 2023 at 4:12:03?AM UTC+10, Lasse Langwadt Christensen wrote:
søndag den 7. maj 2023 kl. 19.18.45 UTC+2 skrev Anthony William Sloman:
On Monday, May 8, 2023 at 2:50:29?AM UTC+10, Lasse Langwadt Christensen wrote:
søndag den 7. maj 2023 kl. 18.18.16 UTC+2 skrev Anthony William Sloman:
On Monday, May 8, 2023 at 1:50:12?AM UTC+10, Lasse Langwadt Christensen wrote:
søndag den 7. maj 2023 kl. 17.26.17 UTC+2 skrev Anthony William Sloman:
On Monday, May 8, 2023 at 12:22:13?AM UTC+10, John Larkin wrote:
On Sun, 7 May 2023 13:09:33 +0100, Martin Brown <\'\'\'newspam\'\'\'@nonad.co.uk> wrote:
On 06/05/2023 03:10, John Larkin wrote:
snip
Otherwise you will end up too sensitive to the channel with the lowest resistance at ambient temperature.
The thermistors are 2% resistance accuracy at 25c.
Cheap ones might be. Interchangeable thermistors do rather better.
I liked the Betathherm 0.2C interchangeable parts. That 0.8% accuracy. Yellow Springs thermistors coukld do better, but they cost even more.
Diodes dV/dT in series might be more reproducible.
Or LM45s, but they have too many quirks.
https://www.ti.com/lit/ds/symlink/lm45.pdf?ts=1683472832545&ref_url=https%253A%252F%252Fwww.ti.com%252Fproduct%252FLM45
It\'s a 12 page data sheet (with eight extra pages for the package details). John Larkin seems to get quirked out easily.
he\'s just experienced and knows the datasheet rarely tells the whole story, afaict the LM45 is notorious for being prone to latchup, oscillation and generally finicky.
But he couldn\'t be bothered to spell out how it is quirky.
If you are posting here as an experienced person as bit more detail is expected, though perhaps not from John who is fishing for flattery rather than being helpful.
Restoring Lasse\'s snip
Figures 16 and 17 in the data sheet make it clear that it is intolerant of capacitative loads. If you didn\'t read the data sheet this might come as a surprise.
Latchup isn\'t mentioned. If you can provoke the device into oscillation I suppose anything is possible. Getting the output above the supply rail can provoke all sort of odd behavior, and getting the output below the negative rail can inject charge carriers into the substrate, which can be even worse.
your snarky comments aren\'t helpful, what was your point?
Since you snipped the point, and didn\'t mark the snip, your own comment is pretty snarky, and not exactly helpful. Your comment could be read as an admission that you had tried to use the LM45 without reading the data sheet, and hadn\'t worked out what you\'d done wrong before giving up on the device.
and your cranky post that you have never used it and think you know better than everyone else.
I certainly looked at using it from time to time, and I do get the impression that neither you nor John Larkin have looked at the data sheet all that carefully.
If it had proved to crankier than that I would have like to have learned how.
if you never used it and only read the data sheet how would you know?
It\'s called book knowledge and background information. You can find out quite a bit without going to the trouble of buying a few parts and playing with them, and this frequently lets you off some tine-consuming experimentation. Engineers do go in for that sort of thing. Tinkerers don\'t have the option.
and listening to those who have real experience might reveal what isn\'t in the books and save you from some time-consuming failures
søndag den 7. maj 2023 kl. 20.45.41 UTC+2 skrev Anthony William Sloman:
On Monday, May 8, 2023 at 4:12:03â¯AM UTC+10, Lasse Langwadt Christensen wrote:
søndag den 7. maj 2023 kl. 19.18.45 UTC+2 skrev Anthony William Sloman:
On Monday, May 8, 2023 at 2:50:29â¯AM UTC+10, Lasse Langwadt Christensen wrote:
søndag den 7. maj 2023 kl. 18.18.16 UTC+2 skrev Anthony William Sloman:
On Monday, May 8, 2023 at 1:50:12â¯AM UTC+10, Lasse Langwadt Christensen wrote:
søndag den 7. maj 2023 kl. 17.26.17 UTC+2 skrev Anthony William Sloman:
On Monday, May 8, 2023 at 12:22:13â¯AM UTC+10, John Larkin wrote:
On Sun, 7 May 2023 13:09:33 +0100, Martin Brown <\'\'\'newspam\'\'\'@nonad.co.uk> wrote:
On 06/05/2023 03:10, John Larkin wrote:
snip
Otherwise you will end up too sensitive to the channel with the lowest resistance at ambient temperature.
The thermistors are 2% resistance accuracy at 25c.
Cheap ones might be. Interchangeable thermistors do rather better.
I liked the Betathherm 0.2C interchangeable parts. That 0.8% accuracy. Yellow Springs thermistors coukld do better, but they cost even more.
Diodes dV/dT in series might be more reproducible.
Or LM45s, but they have too many quirks.
https://www.ti.com/lit/ds/symlink/lm45.pdf?ts=1683472832545&ref_url=https%253A%252F%252Fwww.ti.com%252Fproduct%252FLM45
It\'s a 12 page data sheet (with eight extra pages for the package details). John Larkin seems to get quirked out easily.
he\'s just experienced and knows the datasheet rarely tells the whole story, afaict the LM45 is notorious for being prone to latchup, oscillation and generally finicky.
But he couldn\'t be bothered to spell out how it is quirky.
If you are posting here as an experienced person as bit more detail is expected, though perhaps not from John who is fishing for flattery rather than being helpful.
Restoring Lasse\'s snip
Figures 16 and 17 in the data sheet make it clear that it is intolerant of capacitative loads. If you didn\'t read the data sheet this might come as a surprise.
Latchup isn\'t mentioned. If you can provoke the device into oscillation I suppose anything is possible. Getting the output above the supply rail can provoke all sort of odd behavior, and getting the output below the negative rail can inject charge carriers into the substrate, which can be even worse.
your snarky comments aren\'t helpful, what was your point?
Since you snipped the point, and didn\'t mark the snip, your own comment is pretty snarky, and not exactly helpful. Your comment could be read as an admission that you had tried to use the LM45 without reading the data sheet, and hadn\'t worked out what you\'d done wrong before giving up on the device.
and your cranky post that you have never used it and think you know better than everyone else.
I certainly looked at using it from time to time, and I do get the impression that neither you nor John Larkin have looked at the data sheet all that carefully.
If it had proved to crankier than that I would have like to have learned how.
if you never used it and only read the data sheet how would you know?
It\'s called book knowledge and background information. You can find out quite a bit without going to the trouble of buying a few parts and playing with them, and this frequently lets you off some tine-consuming experimentation. Engineers do go in for that sort of thing. Tinkerers don\'t have the option.
and listening to those who have real experience might reveal what isn\'t in the books and save you from some time-consuming failures.
On Sun, 7 May 2023 12:35:44 -0700 (PDT), Lasse Langwadt Christensen
lang...@fonz.dk> wrote:
søndag den 7. maj 2023 kl. 20.45.41 UTC+2 skrev Anthony William Sloman:
On Monday, May 8, 2023 at 4:12:03?AM UTC+10, Lasse Langwadt Christensen wrote:
søndag den 7. maj 2023 kl. 19.18.45 UTC+2 skrev Anthony William Sloman:
On Monday, May 8, 2023 at 2:50:29?AM UTC+10, Lasse Langwadt Christensen wrote:
søndag den 7. maj 2023 kl. 18.18.16 UTC+2 skrev Anthony William Sloman:
On Monday, May 8, 2023 at 1:50:12?AM UTC+10, Lasse Langwadt Christensen wrote:
søndag den 7. maj 2023 kl. 17.26.17 UTC+2 skrev Anthony William Sloman:
On Monday, May 8, 2023 at 12:22:13?AM UTC+10, John Larkin wrote:
On Sun, 7 May 2023 13:09:33 +0100, Martin Brown <\'\'\'newspam\'\'\'@nonad.co.uk> wrote:
On 06/05/2023 03:10, John Larkin wrote:
Otherwise you will end up too sensitive to the channel with the lowest resistance at ambient temperature.
The thermistors are 2% resistance accuracy at 25c.
Cheap ones might be. Interchangeable thermistors do rather better.
I liked the Betathherm 0.2C interchangeable parts. That 0.8% accuracy. Yellow Springs thermistors coukld do better, but they cost even more.
Diodes dV/dT in series might be more reproducible.
Or LM45s, but they have too many quirks.
https://www.ti.com/lit/ds/symlink/lm45.pdf?ts=1683472832545&ref_url=https%253A%252F%252Fwww.ti.com%252Fproduct%252FLM45
It\'s a 12 page data sheet (with eight extra pages for the package details). John Larkin seems to get quirked out easily.
he\'s just experienced and knows the datasheet rarely tells the whole story, afaict the LM45 is notorious for being prone to latchup, oscillation and generally finicky.
But he couldn\'t be bothered to spell out how it is quirky.
If you are posting here as an experienced person as bit more detail is expected, though perhaps not from John who is fishing for flattery rather than being helpful.
Restoring Lasse\'s snip
Figures 16 and 17 in the data sheet make it clear that it is intolerant of capacitative loads. If you didn\'t read the data sheet this might come as a surprise.
Latchup isn\'t mentioned. If you can provoke the device into oscillation I suppose anything is possible. Getting the output above the supply rail can provoke all sort of odd behavior, and getting the output below the negative rail can inject charge carriers into the substrate, which can be even worse.
your snarky comments aren\'t helpful, what was your point?
Since you snipped the point, and didn\'t mark the snip, your own comment is pretty snarky, and not exactly helpful. Your comment could be read as an admission that you had tried to use the LM45 without reading the data sheet, and hadn\'t worked out what you\'d done wrong before giving up on the device.
and your cranky post that you have never used it and think you know better than everyone else.
I certainly looked at using it from time to time, and I do get the impression that neither you nor John Larkin have looked at the data sheet all that carefully.
If it had proved to crankier than that I would have like to have learned how.
if you never used it and only read the data sheet how would you know?
It\'s called book knowledge and background information. You can find out quite a bit without going to the trouble of buying a few parts and playing with them, and this frequently lets you off some tine-consuming experimentation. Engineers do go in for that sort of thing. Tinkerers don\'t have the option.
and listening to those who have real experience might reveal what isn\'t in the books and save you from some time-consuming failures
One learns remarkable things - not on data sheets - by testing and using real parts and circuits.
A given part number, like a 2N part, can be very different from different suppliers. I the US you can\'t trademark a part number, so many crazy sources exist for, say,
MAX809... not at all the same die.
søndag den 7. maj 2023 kl. 18.48.56 UTC+2 skrev John Larkin:
On Sun, 7 May 2023 08:00:22 -0700 (PDT), Lasse Langwadt Christensen
lang...@fonz.dk> wrote:
søndag den 7. maj 2023 kl. 01.16.17 UTC+2 skrev Phil Hobbs:
On 2023-05-06 16:55, John Larkin wrote:
On Sat, 6 May 2023 13:18:18 -0700 (PDT), Lasse Langwadt Christensen
lang...@fonz.dk> wrote:
lørdag den 6. maj 2023 kl. 21.52.56 UTC+2 skrev John Larkin:
On Sat, 6 May 2023 10:22:38 -0700 (PDT), Lasse Langwadt Christensen
lang...@fonz.dk> wrote:
lørdag den 6. maj 2023 kl. 17.56.04 UTC+2 skrev John Larkin:
On Sat, 6 May 2023 16:25:19 +0100, l...@poppyrecords.invalid.invalid
(Liz Tuddenham) wrote:
John Larkin <jla...@highlandSNIPMEtechnology.com> wrote:
Imagine a chassis with up to eight plugin boards. The chassis has a
pair of PWM controlled fans.
https://www.dropbox.com/s/8ubv5if7cbnsjzn/P940-8_front.jpg?raw=1
Each board will have a thermistor to sense board temperature. If any
board thinks it\'s too hot, it asks the fan controller to jog the fan
speeds up a notch. If nobody requests more air, the controller jogs
them down. That will work.
But I have a board with eight channels that can each get hot. There\'s
no place on the board that represents the worst-channel temperature. I
only have two available ADC channels so I can\'t use eight thermistors.
But thermistors are radically nonlinear. If I parallel four
thermistors into each ADC channel, the hottest of the four will
dominate. That should work well enough.
Some sort of diode thing might select the hottest thermistor, but
paralleling is easy.
Use 1N4148 (or equivalent) diodes in parallel and a constant feed of
1mA; the hottest one is the only one you are interested in and that one
will determine the voltage drop across the whole circuit. I did exactly
this with the thermal protection of a large amplifier where each output
transistor had its own heatsink.
That would behave similar to the parallel thermistors. The diode drops
would be about -2 mV per degree c and the current per diode would be
about 60 mV per decade. The result is a weighted temperature average.
Thanks for the suggestion. We have lots of single and dual
surface-mount diodes. Dual would double the signal.
maybe scan by grounding each diode in turn with an FPGA output?
Version 4
SHEET 1 920 820
WIRE 192 16 32 16
WIRE 464 16 272 16
WIRE 640 16 464 16
WIRE 848 16 640 16
WIRE 32 32 32 16
WIRE 272 48 272 16
WIRE 464 48 464 16
WIRE 640 48 640 16
WIRE 272 192 272 112
WIRE 464 192 464 112
WIRE 640 192 640 112
WIRE 272 304 272 272
WIRE 464 304 464 272
WIRE 464 304 272 304
WIRE 640 304 640 272
WIRE 640 304 464 304
FLAG 32 112 0
FLAG 272 304 0
FLAG 848 16 Vout
SYMBOL diode 256 48 R0
WINDOW 123 22 83 Left 2
SYMATTR InstName D1
SYMATTR Value 1N4148
SYMATTR Value2 temp={T}
SYMBOL res 176 32 R270
WINDOW 0 32 56 VTop 2
WINDOW 3 0 56 VBottom 2
SYMATTR InstName R1
SYMATTR Value 50k
SYMBOL voltage 32 16 R0
WINDOW 123 0 0 Left 0
WINDOW 39 0 0 Left 0
SYMATTR InstName V1
SYMATTR Value 3
SYMBOL diode 448 48 R0
SYMATTR InstName D3
SYMATTR Value 1N4148
SYMBOL voltage 272 176 R0
WINDOW 3 -5 161 VRight 2
WINDOW 123 0 0 Left 0
WINDOW 39 0 0 Left 0
SYMATTR InstName V2
SYMATTR Value PULSE(3 0 0 1u 1u 1m 3m)
SYMBOL diode 624 48 R0
SYMATTR InstName D2
SYMATTR Value 1N4148
SYMBOL voltage 464 176 R0
WINDOW 3 -5 161 VRight 2
WINDOW 123 0 0 Left 0
WINDOW 39 0 0 Left 0
SYMATTR InstName V3
SYMATTR Value PULSE(3 0 1m 1u 1u 1m 3m)
SYMBOL voltage 640 176 R0
WINDOW 3 -5 161 VRight 2
WINDOW 123 0 0 Left 0
WINDOW 39 0 0 Left 0
SYMATTR InstName V4
SYMATTR Value PULSE(3 0 2m 1u 1u 1m 3m)
TEXT -2 296 Left 2 !.tran 0 10m 1u
TEXT 208 -200 Left 2 !.step param T 25 100 5
LT Spice aborts that, \"unknown syntax\" error.
weird, I just tried it and it works here
https://imgur.com/a/ZKWEVur
Found it. There were three strange \"blank\" lines at the end of the
.asc that it didn\'t like.
That\'s sneaky, using the diodes as their own mux.
In the early \'90s, I built a diffraction-based sensor as an online
monitor for post-exposure bake in semiconductor lithography that worked
like that. It had seven 1 x 3 inch solar cells arranged in a cone (like
a poker hand, but 360 degrees).
All the cathodes were connected to a TIA together, and the anodes were
grounded one at a time, using a zero-power PAL with tri-state outputs.
(A PALCE22V10Z, iirc.) It had to be 3-state, because a logic high would
have forward-biased the solar cells. The photocurrent was pretty small,
so even a 1990 CMOS output resistance was negligible.
A normal PAL might not have worked, even in 3-state, because their low
output levels weren\'t that well controlled.
Lasse\'s suggestion is a bit different because the selected diode is
forward-biased, so a totem-pole output would be OK as long as it goes to
0V accurately enough.
Dunno about FPGAs--do their outputs really go to ground like that?
here\'s the plot of the Artix7 LVCMOS33 pull down from the ibis file (min/max/typ)
https://imgur.com/a/qFTQwNg
I wonder how real that is. The grounds around the chip aren\'t really
zero ohms to pcb ground.
the slope around zero is roughly 25 Ohm
On Sun, 7 May 2023 09:55:51 -0700 (PDT), Lasse Langwadt Christensen
lang...@fonz.dk> wrote:
søndag den 7. maj 2023 kl. 18.48.56 UTC+2 skrev John Larkin:
On Sun, 7 May 2023 08:00:22 -0700 (PDT), Lasse Langwadt Christensen
lang...@fonz.dk> wrote:
søndag den 7. maj 2023 kl. 01.16.17 UTC+2 skrev Phil Hobbs:
On 2023-05-06 16:55, John Larkin wrote:
On Sat, 6 May 2023 13:18:18 -0700 (PDT), Lasse Langwadt Christensen
lang...@fonz.dk> wrote:
lørdag den 6. maj 2023 kl. 21.52.56 UTC+2 skrev John Larkin:
On Sat, 6 May 2023 10:22:38 -0700 (PDT), Lasse Langwadt Christensen
lang...@fonz.dk> wrote:
lørdag den 6. maj 2023 kl. 17.56.04 UTC+2 skrev John Larkin:
On Sat, 6 May 2023 16:25:19 +0100, l...@poppyrecords.invalid.invalid
(Liz Tuddenham) wrote:
John Larkin <jla...@highlandSNIPMEtechnology.com> wrote:
Imagine a chassis with up to eight plugin boards. The chassis has a
pair of PWM controlled fans.
https://www.dropbox.com/s/8ubv5if7cbnsjzn/P940-8_front.jpg?raw=1
Each board will have a thermistor to sense board temperature. If any
board thinks it\'s too hot, it asks the fan controller to jog the fan
speeds up a notch. If nobody requests more air, the controller jogs
them down. That will work.
But I have a board with eight channels that can each get hot. There\'s
no place on the board that represents the worst-channel temperature. I
only have two available ADC channels so I can\'t use eight thermistors.
But thermistors are radically nonlinear. If I parallel four
thermistors into each ADC channel, the hottest of the four will
dominate. That should work well enough.
Some sort of diode thing might select the hottest thermistor, but
paralleling is easy.
Use 1N4148 (or equivalent) diodes in parallel and a constant feed of
1mA; the hottest one is the only one you are interested in and that one
will determine the voltage drop across the whole circuit. I did exactly
this with the thermal protection of a large amplifier where each output
transistor had its own heatsink.
That would behave similar to the parallel thermistors. The diode drops
would be about -2 mV per degree c and the current per diode would be
about 60 mV per decade. The result is a weighted temperature average.
Thanks for the suggestion. We have lots of single and dual
surface-mount diodes. Dual would double the signal.
maybe scan by grounding each diode in turn with an FPGA output?
Version 4
SHEET 1 920 820
WIRE 192 16 32 16
WIRE 464 16 272 16
WIRE 640 16 464 16
WIRE 848 16 640 16
WIRE 32 32 32 16
WIRE 272 48 272 16
WIRE 464 48 464 16
WIRE 640 48 640 16
WIRE 272 192 272 112
WIRE 464 192 464 112
WIRE 640 192 640 112
WIRE 272 304 272 272
WIRE 464 304 464 272
WIRE 464 304 272 304
WIRE 640 304 640 272
WIRE 640 304 464 304
FLAG 32 112 0
FLAG 272 304 0
FLAG 848 16 Vout
SYMBOL diode 256 48 R0
WINDOW 123 22 83 Left 2
SYMATTR InstName D1
SYMATTR Value 1N4148
SYMATTR Value2 temp={T}
SYMBOL res 176 32 R270
WINDOW 0 32 56 VTop 2
WINDOW 3 0 56 VBottom 2
SYMATTR InstName R1
SYMATTR Value 50k
SYMBOL voltage 32 16 R0
WINDOW 123 0 0 Left 0
WINDOW 39 0 0 Left 0
SYMATTR InstName V1
SYMATTR Value 3
SYMBOL diode 448 48 R0
SYMATTR InstName D3
SYMATTR Value 1N4148
SYMBOL voltage 272 176 R0
WINDOW 3 -5 161 VRight 2
WINDOW 123 0 0 Left 0
WINDOW 39 0 0 Left 0
SYMATTR InstName V2
SYMATTR Value PULSE(3 0 0 1u 1u 1m 3m)
SYMBOL diode 624 48 R0
SYMATTR InstName D2
SYMATTR Value 1N4148
SYMBOL voltage 464 176 R0
WINDOW 3 -5 161 VRight 2
WINDOW 123 0 0 Left 0
WINDOW 39 0 0 Left 0
SYMATTR InstName V3
SYMATTR Value PULSE(3 0 1m 1u 1u 1m 3m)
SYMBOL voltage 640 176 R0
WINDOW 3 -5 161 VRight 2
WINDOW 123 0 0 Left 0
WINDOW 39 0 0 Left 0
SYMATTR InstName V4
SYMATTR Value PULSE(3 0 2m 1u 1u 1m 3m)
TEXT -2 296 Left 2 !.tran 0 10m 1u
TEXT 208 -200 Left 2 !.step param T 25 100 5
LT Spice aborts that, \"unknown syntax\" error.
weird, I just tried it and it works here
https://imgur.com/a/ZKWEVur
Found it. There were three strange \"blank\" lines at the end of the
.asc that it didn\'t like.
That\'s sneaky, using the diodes as their own mux.
In the early \'90s, I built a diffraction-based sensor as an online
monitor for post-exposure bake in semiconductor lithography that worked
like that. It had seven 1 x 3 inch solar cells arranged in a cone (like
a poker hand, but 360 degrees).
All the cathodes were connected to a TIA together, and the anodes were
grounded one at a time, using a zero-power PAL with tri-state outputs.
(A PALCE22V10Z, iirc.) It had to be 3-state, because a logic high would
have forward-biased the solar cells. The photocurrent was pretty small,
so even a 1990 CMOS output resistance was negligible.
A normal PAL might not have worked, even in 3-state, because their low
output levels weren\'t that well controlled.
Lasse\'s suggestion is a bit different because the selected diode is
forward-biased, so a totem-pole output would be OK as long as it goes to
0V accurately enough.
Dunno about FPGAs--do their outputs really go to ground like that?
here\'s the plot of the Artix7 LVCMOS33 pull down from the ibis file (min/max/typ)
https://imgur.com/a/qFTQwNg
I wonder how real that is. The grounds around the chip aren\'t really
zero ohms to pcb ground.
the slope around zero is roughly 25 Ohm
But ground may not be ground.
It would be interesting to characterize logic low vs chip current (for
various pins!) but that would be a project.
Most FPGAs have programmable drive strength too. Bigger project.
I can imagine making a DAC from gpio pins and some resistors, either a
ladder or just delta-sigma. We do delta-sigma but with an outboard
tiny-logic cmos buffer.
mandag den 8. maj 2023 kl. 18.44.25 UTC+2 skrev John Larkin:
On Sun, 7 May 2023 09:55:51 -0700 (PDT), Lasse Langwadt Christensen
lang...@fonz.dk> wrote:
søndag den 7. maj 2023 kl. 18.48.56 UTC+2 skrev John Larkin:
On Sun, 7 May 2023 08:00:22 -0700 (PDT), Lasse Langwadt Christensen
lang...@fonz.dk> wrote:
søndag den 7. maj 2023 kl. 01.16.17 UTC+2 skrev Phil Hobbs:
On 2023-05-06 16:55, John Larkin wrote:
On Sat, 6 May 2023 13:18:18 -0700 (PDT), Lasse Langwadt Christensen
lang...@fonz.dk> wrote:
lørdag den 6. maj 2023 kl. 21.52.56 UTC+2 skrev John Larkin:
On Sat, 6 May 2023 10:22:38 -0700 (PDT), Lasse Langwadt Christensen
lang...@fonz.dk> wrote:
lørdag den 6. maj 2023 kl. 17.56.04 UTC+2 skrev John Larkin:
On Sat, 6 May 2023 16:25:19 +0100, l...@poppyrecords.invalid.invalid
(Liz Tuddenham) wrote:
John Larkin <jla...@highlandSNIPMEtechnology.com> wrote:
Imagine a chassis with up to eight plugin boards. The chassis has a
pair of PWM controlled fans.
https://www.dropbox.com/s/8ubv5if7cbnsjzn/P940-8_front.jpg?raw=1
Each board will have a thermistor to sense board temperature. If any
board thinks it\'s too hot, it asks the fan controller to jog the fan
speeds up a notch. If nobody requests more air, the controller jogs
them down. That will work.
But I have a board with eight channels that can each get hot. There\'s
no place on the board that represents the worst-channel temperature. I
only have two available ADC channels so I can\'t use eight thermistors.
But thermistors are radically nonlinear. If I parallel four
thermistors into each ADC channel, the hottest of the four will
dominate. That should work well enough.
Some sort of diode thing might select the hottest thermistor, but
paralleling is easy.
Use 1N4148 (or equivalent) diodes in parallel and a constant feed of
1mA; the hottest one is the only one you are interested in and that one
will determine the voltage drop across the whole circuit. I did exactly
this with the thermal protection of a large amplifier where each output
transistor had its own heatsink.
That would behave similar to the parallel thermistors. The diode drops
would be about -2 mV per degree c and the current per diode would be
about 60 mV per decade. The result is a weighted temperature average.
Thanks for the suggestion. We have lots of single and dual
surface-mount diodes. Dual would double the signal.
maybe scan by grounding each diode in turn with an FPGA output?
Version 4
SHEET 1 920 820
WIRE 192 16 32 16
WIRE 464 16 272 16
WIRE 640 16 464 16
WIRE 848 16 640 16
WIRE 32 32 32 16
WIRE 272 48 272 16
WIRE 464 48 464 16
WIRE 640 48 640 16
WIRE 272 192 272 112
WIRE 464 192 464 112
WIRE 640 192 640 112
WIRE 272 304 272 272
WIRE 464 304 464 272
WIRE 464 304 272 304
WIRE 640 304 640 272
WIRE 640 304 464 304
FLAG 32 112 0
FLAG 272 304 0
FLAG 848 16 Vout
SYMBOL diode 256 48 R0
WINDOW 123 22 83 Left 2
SYMATTR InstName D1
SYMATTR Value 1N4148
SYMATTR Value2 temp={T}
SYMBOL res 176 32 R270
WINDOW 0 32 56 VTop 2
WINDOW 3 0 56 VBottom 2
SYMATTR InstName R1
SYMATTR Value 50k
SYMBOL voltage 32 16 R0
WINDOW 123 0 0 Left 0
WINDOW 39 0 0 Left 0
SYMATTR InstName V1
SYMATTR Value 3
SYMBOL diode 448 48 R0
SYMATTR InstName D3
SYMATTR Value 1N4148
SYMBOL voltage 272 176 R0
WINDOW 3 -5 161 VRight 2
WINDOW 123 0 0 Left 0
WINDOW 39 0 0 Left 0
SYMATTR InstName V2
SYMATTR Value PULSE(3 0 0 1u 1u 1m 3m)
SYMBOL diode 624 48 R0
SYMATTR InstName D2
SYMATTR Value 1N4148
SYMBOL voltage 464 176 R0
WINDOW 3 -5 161 VRight 2
WINDOW 123 0 0 Left 0
WINDOW 39 0 0 Left 0
SYMATTR InstName V3
SYMATTR Value PULSE(3 0 1m 1u 1u 1m 3m)
SYMBOL voltage 640 176 R0
WINDOW 3 -5 161 VRight 2
WINDOW 123 0 0 Left 0
WINDOW 39 0 0 Left 0
SYMATTR InstName V4
SYMATTR Value PULSE(3 0 2m 1u 1u 1m 3m)
TEXT -2 296 Left 2 !.tran 0 10m 1u
TEXT 208 -200 Left 2 !.step param T 25 100 5
LT Spice aborts that, \"unknown syntax\" error.
weird, I just tried it and it works here
https://imgur.com/a/ZKWEVur
Found it. There were three strange \"blank\" lines at the end of the
.asc that it didn\'t like.
That\'s sneaky, using the diodes as their own mux.
In the early \'90s, I built a diffraction-based sensor as an online
monitor for post-exposure bake in semiconductor lithography that worked
like that. It had seven 1 x 3 inch solar cells arranged in a cone (like
a poker hand, but 360 degrees).
All the cathodes were connected to a TIA together, and the anodes were
grounded one at a time, using a zero-power PAL with tri-state outputs.
(A PALCE22V10Z, iirc.) It had to be 3-state, because a logic high would
have forward-biased the solar cells. The photocurrent was pretty small,
so even a 1990 CMOS output resistance was negligible.
A normal PAL might not have worked, even in 3-state, because their low
output levels weren\'t that well controlled.
Lasse\'s suggestion is a bit different because the selected diode is
forward-biased, so a totem-pole output would be OK as long as it goes to
0V accurately enough.
Dunno about FPGAs--do their outputs really go to ground like that?
here\'s the plot of the Artix7 LVCMOS33 pull down from the ibis file (min/max/typ)
https://imgur.com/a/qFTQwNg
I wonder how real that is. The grounds around the chip aren\'t really
zero ohms to pcb ground.
the slope around zero is roughly 25 Ohm
But ground may not be ground.
with +/-50mV specs for voltage the ground must be pretty stiff
in the IBIS the ground clamps in an input looks like ~1 Ohm
It would be interesting to characterize logic low vs chip current (for
various pins!) but that would be a project.
Most FPGAs have programmable drive strength too. Bigger project.
it is all in the IBIS, pulldown with max drive strength looks like ~9 Ohm
I can imagine making a DAC from gpio pins and some resistors, either a
ladder or just delta-sigma. We do delta-sigma but with an outboard
tiny-logic cmos buffer.
you could use tiny-logic cmos buffers for an R2R DAC too
the big advantage of delta-sigma (when you don\'t need speed) is that
it\'s only one pin so it\'ll always be linear