Detecting... load, current... um...

[Tim Wescott]

On Tue, 30 Jun 2015 17:14:50 -0700, scott.a.mayo wrote:

Now sure how to describe the problem in few words, sorry.

I have two circuit boards (to be designed), A and B. A has the power
supply. A and B will be connected by a longish, 2 conductor wire. The
wire will be used to supply 12V+ and ground from A to B. B has no other
source of power.

B needs to signal A when something happens.

For various reasons, I can't replace the wire with a 3 conductor
version, and wireless solutions aren't practical.

Normally, board B draws maybe 60mA at most, mostly for LEDs. But
occasionally board B will close a relay, and feed the 12V into a larger
load: a DC-DC converter, to generate 5V @ maybe 1-3A. Presumably that
will show up as a larger current draw on the 12V line, but I don't know
how much. (I can slap a high wattage resistor in parallel with the load
to make it draw more current, if that helps.)

That's what A has to detect.

I don't know how to detect current changes and I don't entirely trust my
estimates on the current change anyway.

Is there a clever and inexpensive way to overlay some sort of signal on
the wire that is reliably detectable? Or is there an easily adjustable
way to detect current changes on a power line? It is probably safe to
say that B draws considerably less than 500mA normally and something
over 500mA during the event.

TIA.

Not what you're asking about, but why a relay to turn on the switching
supply? If it shares a common ground with your supply line, why not
switch power with a PMOS, or just switch the enable line on the switching
supply?

--
www.wescottdesign.com

 

On Wednesday, July 1, 2015 at 4:25:37 PM UTC-4, Tim Wescott wrote:

On Tue, 30 Jun 2015 17:14:50 -0700, scott.a.mayo wrote:

Now sure how to describe the problem in few words, sorry.

I have two circuit boards (to be designed), A and B. A has the power
supply. A and B will be connected by a longish, 2 conductor wire. The
wire will be used to supply 12V+ and ground from A to B. B has no other
source of power.

B needs to signal A when something happens.

For various reasons, I can't replace the wire with a 3 conductor
version, and wireless solutions aren't practical.

Normally, board B draws maybe 60mA at most, mostly for LEDs. But
occasionally board B will close a relay, and feed the 12V into a larger
load: a DC-DC converter, to generate 5V @ maybe 1-3A. Presumably that
will show up as a larger current draw on the 12V line, but I don't know
how much. (I can slap a high wattage resistor in parallel with the load
to make it draw more current, if that helps.)

That's what A has to detect.

I don't know how to detect current changes and I don't entirely trust my
estimates on the current change anyway.

Is there a clever and inexpensive way to overlay some sort of signal on
the wire that is reliably detectable? Or is there an easily adjustable
way to detect current changes on a power line? It is probably safe to
say that B draws considerably less than 500mA normally and something
over 500mA during the event.

TIA.

Not what you're asking about, but why a relay to turn on the switching
supply? If it shares a common ground with your supply line, why not
switch power with a PMOS, or just switch the enable line on the switching
supply?

It might be feasible. The relay has the NC output that I have other plans for, but that could be worked around. I think I just unconsciously avoided silicon to switch it on and off, because I have no idea how the converter behaves with regard to inrush current, back spikes when turned off, etc. and I figured I'd rather the relay contacts took the abuse than silicon.

The 12vdc->5V5A converter is something I already have and it doesn't have niceties like enable lines; you feed it 12v DC and out comes 5V, common ground.

 

[Phil Allison]

George Herold wrote:

** Probably I should explain that a bit more.

The coil wound around the reed switch *replaces* the previously mentioned resistor in line with the 12V DC supply.

Adjust the number of turns ( which may be wound on a plastic tube for convenience ) so the reed switch reliably closes when the current reaches the higher level.

A 20mm long reed switch operates in less than a millisecond and needs about 20 turns at 1 amp DC.



That's a neat idea Phil. Would it work with the wire just wrapped
around the body of the reed switch?

** Yep, I did just that with one of the larger types using 10 turns of 1.2mm dia wire. The contacts closed at about 22amps, setting off an audible warning of current overload in a RC model boat - in case of weed pickup or a plastic bag fouling the prop.

OK how the "bleep" does a reed relay work, with the field along it's axis?

** Well, the field magnetises any iron inside the coil just like a solenoid.

The two reeds become magnetised N-S and N-S with N and S facing across the gap.


..... Phil

 

[John Fields]

On Wed, 1 Jul 2015 18:12:10 -0700 (PDT), scott.a.mayo@gmail.com
wrote:

On Wednesday, July 1, 2015 at 4:25:37 PM UTC-4, Tim Wescott wrote:
On Tue, 30 Jun 2015 17:14:50 -0700, scott.a.mayo wrote:

Now sure how to describe the problem in few words, sorry.

I have two circuit boards (to be designed), A and B. A has the power
supply. A and B will be connected by a longish, 2 conductor wire. The
wire will be used to supply 12V+ and ground from A to B. B has no other
source of power.

B needs to signal A when something happens.

For various reasons, I can't replace the wire with a 3 conductor
version, and wireless solutions aren't practical.

Normally, board B draws maybe 60mA at most, mostly for LEDs. But
occasionally board B will close a relay, and feed the 12V into a larger
load: a DC-DC converter, to generate 5V @ maybe 1-3A. Presumably that
will show up as a larger current draw on the 12V line, but I don't know
how much. (I can slap a high wattage resistor in parallel with the load
to make it draw more current, if that helps.)

That's what A has to detect.

I don't know how to detect current changes and I don't entirely trust my
estimates on the current change anyway.

Is there a clever and inexpensive way to overlay some sort of signal on
the wire that is reliably detectable? Or is there an easily adjustable
way to detect current changes on a power line? It is probably safe to
say that B draws considerably less than 500mA normally and something
over 500mA during the event.

TIA.

Not what you're asking about, but why a relay to turn on the switching
supply? If it shares a common ground with your supply line, why not
switch power with a PMOS, or just switch the enable line on the switching
supply?


It might be feasible. The relay has the NC output that I have other plans for, but that could be worked around. I think I just unconsciously avoided silicon to switch it on and off, because I have no idea how the converter behaves with regard to inrush current, back spikes when turned off, etc. and I figured I'd rather the relay contacts took the abuse than silicon.

The 12vdc->5V5A converter is something I already have and it doesn't have niceties like enable lines; you feed it 12v DC and out comes 5V, common ground.

---
Here's a simpler, cheaper way to build the detector, and it's set
for the output to go high when the load current is ~> 1 ampere:

Version 4
SHEET 1 2680 692
WIRE -336 -784 -784 -784
WIRE -1264 -704 -1360 -704
WIRE -1152 -704 -1264 -704
WIRE -1088 -704 -1152 -704
WIRE -960 -704 -1008 -704
WIRE -912 -704 -960 -704
WIRE -784 -704 -784 -784
WIRE -784 -704 -832 -704
WIRE -736 -704 -784 -704
WIRE -272 -704 -384 -704
WIRE -1152 -656 -1152 -704
WIRE -960 -640 -960 -704
WIRE -736 -640 -960 -640
WIRE -272 -640 -384 -640
WIRE -1360 -576 -1360 -704
WIRE -736 -576 -960 -576
WIRE -1152 -528 -1152 -576
WIRE -1152 -528 -1168 -528
WIRE -1152 -512 -1152 -528
WIRE -1088 -512 -1152 -512
WIRE -960 -512 -960 -576
WIRE -960 -512 -1008 -512
WIRE -912 -512 -960 -512
WIRE -784 -512 -832 -512
WIRE -736 -512 -784 -512
WIRE -336 -512 -336 -784
WIRE -336 -512 -384 -512
WIRE -1152 -480 -1152 -512
WIRE -1360 -368 -1360 -496
WIRE -1280 -368 -1360 -368
WIRE -1152 -368 -1152 -400
WIRE -1152 -368 -1280 -368
WIRE -1136 -368 -1152 -368
WIRE -784 -368 -784 -512
WIRE -784 -368 -1136 -368
WIRE -1136 -320 -1136 -368
FLAG -1136 -320 0
FLAG -1168 -528 +12
FLAG -272 -704 +12
FLAG -272 -640 LOAD_ON
FLAG -1264 -704 LOAD_+12
FLAG -1280 -368 LOAD_GND
SYMBOL Opamps\\LTC1541 -560 -608 R0
SYMATTR InstName U1
SYMBOL res -992 -528 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R3
SYMATTR Value 10K
SYMBOL res -816 -528 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R4
SYMATTR Value 75K
SYMBOL res -992 -720 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R1
SYMATTR Value 10K
SYMBOL res -1168 -672 R0
SYMATTR InstName Rs
SYMATTR Value .15
SYMBOL res -816 -720 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R2
SYMATTR Value 75K
SYMBOL current -1360 -576 R0
WINDOW 3 24 80 Invisible 2
WINDOW 123 0 0 Left 2
WINDOW 39 0 0 Left 2
SYMATTR Value PULSE(0 3 0 1 1 1U 2)
SYMATTR InstName Iload
SYMBOL voltage -1152 -496 R0
WINDOW 0 14 102 Left 2
WINDOW 3 24 96 Invisible 2
WINDOW 123 0 0 Left 2
WINDOW 39 0 0 Left 2
SYMATTR InstName V2
SYMATTR Value 12
TEXT -1128 -344 Left 2 !.tran 3 uic

John Fields

 

[amdx]

On 7/1/2015 5:53 AM, Phil Hobbs wrote:

This thread reminded me of a circuit from the 70's.

Anyone remember the car circuit hooked to an 8 track to turn the amp
on when a cassette was inserted?

12 volts was applied to the anode of a diode, the cathode was connected
to the 8 track. A PNP transistor was connected across the diode, emitter
to anode, cathode to base, the collector powered the amplifier.
When current flowed through the diode it biased the PNP on to power the
amp. I think I have that right.

I had that circuit in my 66* Ford Fairlane 500. At 17 the simplicity and
cool factor impressed me.
Mikek

*Cherry red, chrome wheels and glass packs.

 

[whit3rd]

On Tuesday, June 30, 2015 at 10:17:18 PM UTC-7, Phil Allison wrote:

Phil Allison wrote:

** I would use a reed switch with a few dozen turns or so
of wire wound around it - eg:

The coil wound around the reed switch *replaces* the previously mentioned resistor in line with the 12V DC supply.

Adjust the number of turns ( which may be wound on a plastic tube for convenience )

I like the idea, but it may be more practical to use a current-sense amplifier like
<http://datasheets.maximintegrated.com/en/ds/MAX4373-MAX4375.pdf>

and a lot more friendly to the poor guy who opens it up ten years from now and
wants to know how it works... and where he can buy parts to fix it.

 

[Phil Allison]

whit3rd wrote:

** I would use a reed switch with a few dozen turns or so
of wire wound around it - eg:

The coil wound around the reed switch *replaces* the previously mentioned resistor in line with the 12V DC supply.

Adjust the number of turns ( which may be wound on a plastic tube for convenience )

I like the idea, but it may be more practical to use a current-sense amplifier like
http://datasheets.maximintegrated.com/en/ds/MAX4373-MAX4375.pdf

and a lot more friendly to the poor guy who opens it up ten years from now and
wants to know how it works... and where he can buy parts to fix it.

** You for real ?

Some oddball, one maker SMD chip hardly *more likely* to be readily available in ten years than the classic reed switch.


.... Phil

 

This looks perfect. I've been playing around in spice (nice tool) and it looks like I can get detection down to 0.5A by changing r4 to 80K. Is there any reason that's risky?

Many thanks.

 

[whit3rd]

On Friday, July 3, 2015 at 2:17:00 AM UTC-7, Phil Allison wrote:

whit3rd wrote:

...it may be more practical to use a current-sense amplifier like
http://datasheets.maximintegrated.com/en/ds/MAX4373-MAX4375.pdf

** You for real ?

Some oddball, one maker SMD chip hardly *more likely* to be readily available in ten years than the classic reed switch.

It's not about that part number, it's about the whole class of chips that do
current-threshold detection; I just picked that part number because there's
about twenty thousand showing in stock...
LT6108, PAC1720, IR2175, FAN4010, INA300, are other manufacturers' functional
equivalents (but there's not much agreement on pinout and feature set).

 

[John Fields]

On Fri, 3 Jul 2015 06:38:41 -0700 (PDT), scott.a.mayo@gmail.com
wrote:

>This looks perfect. I've been playing around in spice (nice tool) and it looks like I can get detection down to 0.5A by changing r4 to 80K. Is there any reason that's risky?

---
With that mod you've only got about 25 millivolts of input
common-mode headroom on the opamp, but as long as the raw 12 volts
doesn't dip below 12 volts under load you should be OK, and you
might want to consider damping the reference as shown on the data
sheet at:

http://cds.linear.com/docs/en/datasheet/15412fd.pdf

Yageo makes a pretty nice wirewound power resistor - their P/N
PNP300JR-73-0R15 - that you could use for the shunt, and DigiKey has
3846 of them in stock:

http://www.digikey.com/product-detail/en/PNP300JR-73-0R15/0.15AETR-ND/2058854
Also, use 1%'ers for R1, R2, R3, and R4, and make R4 80.6k.

---

>Many thanks.

---
My pleasure.

John Fields

 

[Phil Allison]

whit3rd wrote:

...it may be more practical to use a current-sense amplifier like
http://datasheets.maximintegrated.com/en/ds/MAX4373-MAX4375.pdf

** You for real ?

Some oddball, one maker SMD chip hardly *more likely* to be readily available in ten years than the classic reed switch.

It's not about that part number,

** Nor was my comment only about a particular chip.

You make far too many assumptions.


..... Phil

 

[John Fields]

On Sat, 04 Jul 2015 16:24:12 +1000, John G <john.g@green.com> wrote:

John G has brought this to us :
on 4/07/2015, John Larkin supposed :
On Wed, 1 Jul 2015 10:01:20 -0700 (PDT), George Herold
gherold@teachspin.com> wrote:

On Wednesday, July 1, 2015 at 1:17:18 AM UTC-4, Phil Allison wrote:
Phil Allison wrote:


** I would use a reed switch with a few dozen turns or so of wire wound
around it - eg:

http://www.arunet.co.uk/tkboyd/ec/ec1RehaReedP0331.jpg


** Probably I should explain that a bit more.

The coil wound around the reed switch *replaces* the previously mentioned
resistor in line with the 12V DC supply.

Adjust the number of turns ( which may be wound on a plastic tube for
convenience ) so the reed switch reliably closes when the current reaches
the higher level.

A 20mm long reed switch operates in less than a millisecond and needs
about 20 turns at 1 amp DC.


.... Phil

That's a neat idea Phil. Would it work with the wire just wrapped around
the body of the reed switch? It been decades since I use a reed
switch, but don't you want the magnetic field perpendicular to the
contact.

Axial, usually, a solenoid wound on the reed capsule. A hazard may be
the large pickup-dropoff (Peekup Andropov in CarTalk language) ratio.
A reed may energize at X amps and drop out at X/5.

Reed relays are rare these days, and deserve it.

Mouser has many thousands in stock from about from about $1.20

Actually he needs a reed SWITCH just the glas bit.
Not a reed RELAY which is a box with some windings as well. :-Z

---
It's generally considered to be a reed _switch_ when it's actuated
by a permanent magnet, and a reed _relay_ when it's actuated by an
electromagnet, just like a conventional non-reed relay.

John Fields

 

[John G]

John G has brought this to us :

on 4/07/2015, John Larkin supposed :
On Wed, 1 Jul 2015 10:01:20 -0700 (PDT), George Herold
gherold@teachspin.com> wrote:

On Wednesday, July 1, 2015 at 1:17:18 AM UTC-4, Phil Allison wrote:
Phil Allison wrote:


** I would use a reed switch with a few dozen turns or so of wire wound
around it - eg:

http://www.arunet.co.uk/tkboyd/ec/ec1RehaReedP0331.jpg


** Probably I should explain that a bit more.

The coil wound around the reed switch *replaces* the previously mentioned
resistor in line with the 12V DC supply.

Adjust the number of turns ( which may be wound on a plastic tube for
convenience ) so the reed switch reliably closes when the current reaches
the higher level.

A 20mm long reed switch operates in less than a millisecond and needs
about 20 turns at 1 amp DC.


.... Phil

That's a neat idea Phil. Would it work with the wire just wrapped around
the body of the reed switch? It been decades since I use a reed
switch, but don't you want the magnetic field perpendicular to the
contact.

Axial, usually, a solenoid wound on the reed capsule. A hazard may be
the large pickup-dropoff (Peekup Andropov in CarTalk language) ratio.
A reed may energize at X amps and drop out at X/5.

Reed relays are rare these days, and deserve it.

Mouser has many thousands in stock from about from about $1.20

Actually he needs a reed SWITCH just the glas bit.
Not a reed RELAY which is a box with some windings as well. :-Z

--
John G Sydney.

 

[John Fields]

On Fri, 03 Jul 2015 20:19:12 -0700, John Larkin
<jlarkin@highlandtechnology.com> wrote:

On Wed, 1 Jul 2015 10:01:20 -0700 (PDT), George Herold
gherold@teachspin.com> wrote:

On Wednesday, July 1, 2015 at 1:17:18 AM UTC-4, Phil Allison wrote:
Phil Allison wrote:


** I would use a reed switch with a few dozen turns or so
of wire wound around it - eg:

http://www.arunet.co.uk/tkboyd/ec/ec1RehaReedP0331.jpg


** Probably I should explain that a bit more.

The coil wound around the reed switch *replaces* the previously mentioned resistor in line with the 12V DC supply.

Adjust the number of turns ( which may be wound on a plastic tube for convenience ) so the reed switch reliably closes when the current reaches the higher level.

A 20mm long reed switch operates in less than a millisecond and needs about 20 turns at 1 amp DC.


.... Phil

That's a neat idea Phil. Would it work with the wire just wrapped
around the body of the reed switch? It been decades since I use a reed
switch, but don't you want the magnetic field perpendicular to the contact.

Axial, usually, a solenoid wound on the reed capsule. A hazard may be
the large pickup-dropoff (Peekup Andropov in CarTalk language) ratio.
A reed may energize at X amps and drop out at X/5.

---
That's actually not too shabby, considering most small SPST form A
relays have a must pickup to must release current ratio of around
7:1
---

>Reed relays are rare these days, and deserve it.

---
Unless they have so much stock because nobody's buying them, DigiKey
seems to disagree with you:

http://www.digikey.com/product-search/en?FV=fff40010%2Cfff80368%2Ca700009&k=relay&mnonly=0&newproducts=0&ColumnSort=0&page=1&stock=0&pbfree=0&rohs=0&quantity=&ptm=0&fid=0&pageSize=25

So perhaps misapplication yields disappointing results?

John Fields

 

[John Larkin]

On Wed, 1 Jul 2015 10:01:20 -0700 (PDT), George Herold
<gherold@teachspin.com> wrote:

On Wednesday, July 1, 2015 at 1:17:18 AM UTC-4, Phil Allison wrote:
Phil Allison wrote:


** I would use a reed switch with a few dozen turns or so
of wire wound around it - eg:

http://www.arunet.co.uk/tkboyd/ec/ec1RehaReedP0331.jpg


** Probably I should explain that a bit more.

The coil wound around the reed switch *replaces* the previously mentioned resistor in line with the 12V DC supply.

Adjust the number of turns ( which may be wound on a plastic tube for convenience ) so the reed switch reliably closes when the current reaches the higher level.

A 20mm long reed switch operates in less than a millisecond and needs about 20 turns at 1 amp DC.


.... Phil

That's a neat idea Phil. Would it work with the wire just wrapped
around the body of the reed switch? It been decades since I use a reed
switch, but don't you want the magnetic field perpendicular to the contact.

Axial, usually, a solenoid wound on the reed capsule. A hazard may be
the large pickup-dropoff (Peekup Andropov in CarTalk language) ratio.
A reed may energize at X amps and drop out at X/5.

Reed relays are rare these days, and deserve it.


--

John Larkin Highland Technology, Inc
picosecond timing laser drivers and controllers

jlarkin att highlandtechnology dott com
http://www.highlandtechnology.com

 

[Phil Allison]

John G wrote:

John Larkin supposed :

Reed relays are rare these days, and deserve it.

Mouser has many thousands in stock from about from about $1.20

** Reed switches have been around since 1936 and still used in the millions - heaps on offer on eBay at tiny prices. Supply is clearly no problem.

A hermetically sealed switch that operates in a millisecond by magnetic field, is good for billions of times, suffers no contact corrosion, offers *massive* voltage isolation and is cheap and easy to use will not go away any time soon.

Were once at the heart of most telephone exchanges & BLDC motors.

Special types are available rated to switch up to 10kVDC and RF signals.


.... Phil

 

[John G]

on 4/07/2015, John Larkin supposed :

On Wed, 1 Jul 2015 10:01:20 -0700 (PDT), George Herold
gherold@teachspin.com> wrote:

On Wednesday, July 1, 2015 at 1:17:18 AM UTC-4, Phil Allison wrote:
Phil Allison wrote:


** I would use a reed switch with a few dozen turns or so
of wire wound around it - eg:

http://www.arunet.co.uk/tkboyd/ec/ec1RehaReedP0331.jpg


** Probably I should explain that a bit more.

The coil wound around the reed switch *replaces* the previously mentioned
resistor in line with the 12V DC supply.

Adjust the number of turns ( which may be wound on a plastic tube for
convenience ) so the reed switch reliably closes when the current reaches
the higher level.

A 20mm long reed switch operates in less than a millisecond and needs about
20 turns at 1 amp DC.


.... Phil

That's a neat idea Phil. Would it work with the wire just wrapped
around the body of the reed switch? It been decades since I use a reed
switch, but don't you want the magnetic field perpendicular to the contact.

Axial, usually, a solenoid wound on the reed capsule. A hazard may be
the large pickup-dropoff (Peekup Andropov in CarTalk language) ratio.
A reed may energize at X amps and drop out at X/5.

Reed relays are rare these days, and deserve it.

Mouser has many thousands in stock from about from about $1.20

--
John G Sydney.

 

[Jasen Betts]

On 2015-07-03, whit3rd <whit3rd@gmail.com> wrote:

On Friday, July 3, 2015 at 2:17:00 AM UTC-7, Phil Allison wrote:
whit3rd wrote:

...it may be more practical to use a current-sense amplifier like
http://datasheets.maximintegrated.com/en/ds/MAX4373-MAX4375.pdf

** You for real ?

Some oddball, one maker SMD chip hardly *more likely* to be readily available in ten years than the classic reed switch.

It's not about that part number, it's about the whole class of chips that do
current-threshold detection; I just picked that part number because there's
about twenty thousand showing in stock...
LT6108, PAC1720, IR2175, FAN4010, INA300, are other manufacturers' functional
equivalents (but there's not much agreement on pinout and feature set).

so how do you guess which will be available in 10 years time?

comparitors and resitors seem to have long-term availability.


--
umop apisdn

 

[Phil Allison]

John Fields wrote:

When he buys it it'll be a reed switch,
but when he finishes it it'll be a reed relay.

** With a coil operating voltage of about 1mV, it's not much like other reed relays. Better call it an "overcurrent reed relay".



.... Phil

 

So. My requirements have changed slightly (and for the last time) but I've bumbled around in LTSpice and may have adapted the original solution to my new needs.

My only objection to reed switches is that I've used them before and I tend to break them. As this current device isn't going to get tossed around, I'll experiment with one again. It's a little more difficult to use one now because of the new requirements:

When the dc-dc converter isn't being asked to drive a 5v load believed to consume 3A (might be less or more, it's not actually documented, it's just known to be substantial), it will instead drive 400-450ma of LEDs. So the current sensor has to ignore current below, say, 600ma to be safe, but trigger above that.

Also, I don't do surface mount anything. Even with magnifying visors I just don't have the eyes (and hands) for it. Through-hole all the way - so I went back to John's first design which allowed me to use parts I could handle..

Here's what I came up with in Spice, starting from the previous design offered:

Version 4
SHEET 1 2680 692
WIRE -1072 -1392 -1120 -1392
WIRE -1008 -1392 -1040 -1392
WIRE -944 -1392 -976 -1392
WIRE -880 -1392 -912 -1392
WIRE -816 -1392 -848 -1392
WIRE -752 -1392 -784 -1392
WIRE -688 -1392 -720 -1392
WIRE -624 -1392 -656 -1392
WIRE -560 -1392 -592 -1392
WIRE -496 -1392 -528 -1392
WIRE -432 -1392 -464 -1392
WIRE -368 -1392 -400 -1392
WIRE -304 -1392 -336 -1392
WIRE -240 -1392 -272 -1392
WIRE -160 -1392 -208 -1392
WIRE -1552 -1360 -1632 -1360
WIRE -1120 -1360 -1120 -1392
WIRE -160 -1360 -160 -1392
WIRE -1472 -1344 -1552 -1360
WIRE -1264 -1344 -1472 -1344
WIRE -1056 -1344 -1264 -1344
WIRE -992 -1344 -1056 -1344
WIRE -864 -1344 -912 -1344
WIRE -816 -1344 -864 -1344
WIRE -688 -1344 -736 -1344
WIRE -1264 -1296 -1264 -1344
WIRE -1120 -1296 -1120 -1328
WIRE -1056 -1296 -1056 -1344
WIRE -608 -1296 -608 -1328
WIRE -160 -1296 -160 -1328
WIRE -1504 -1280 -1632 -1280
WIRE -1632 -1248 -1696 -1248
WIRE -1120 -1232 -1120 -1264
WIRE -320 -1232 -320 -1248
WIRE -160 -1232 -160 -1264
WIRE -1696 -1216 -1696 -1248
WIRE -768 -1216 -768 -1232
WIRE -352 -1216 -432 -1216
WIRE -1504 -1200 -1504 -1280
WIRE -1472 -1200 -1504 -1200
WIRE -1408 -1200 -1472 -1200
WIRE -864 -1200 -864 -1344
WIRE -800 -1200 -864 -1200
WIRE -240 -1200 -288 -1200
WIRE -688 -1184 -688 -1344
WIRE -688 -1184 -736 -1184
WIRE -352 -1184 -688 -1184
WIRE -1632 -1168 -1632 -1248
WIRE -1632 -1168 -1648 -1168
WIRE -1600 -1168 -1632 -1168
WIRE -1456 -1168 -1568 -1168
WIRE -1120 -1168 -1120 -1200
WIRE -1056 -1168 -1056 -1216
WIRE -992 -1168 -1056 -1168
WIRE -864 -1168 -912 -1168
WIRE -800 -1168 -864 -1168
WIRE -160 -1168 -160 -1200
WIRE -1616 -1152 -1600 -1168
WIRE -608 -1136 -608 -1216
WIRE -560 -1136 -608 -1136
WIRE -432 -1136 -432 -1216
WIRE -432 -1136 -480 -1136
WIRE -1056 -1120 -1056 -1168
WIRE -1040 -1120 -1056 -1120
WIRE -1120 -1104 -1120 -1136
WIRE -1056 -1104 -1056 -1120
WIRE -864 -1104 -864 -1168
WIRE -160 -1104 -160 -1136
WIRE -1600 -1088 -1616 -1104
WIRE -1600 -1088 -1648 -1088
WIRE -432 -1088 -432 -1136
WIRE -1552 -1072 -1568 -1088
WIRE -1408 -1072 -1408 -1200
WIRE -1408 -1072 -1552 -1072
WIRE -608 -1072 -608 -1136
WIRE -1120 -1040 -1120 -1072
WIRE -160 -1040 -160 -1072
WIRE -1264 -976 -1264 -1216
WIRE -1120 -976 -1120 -1008
WIRE -160 -976 -160 -1008
WIRE -1456 -960 -1456 -1168
WIRE -1456 -960 -1264 -976
WIRE -1056 -960 -1056 -1024
WIRE -1056 -960 -1264 -976
WIRE -1040 -960 -1056 -960
WIRE -864 -960 -864 -1024
WIRE -864 -960 -1040 -960
WIRE -768 -960 -768 -1152
WIRE -768 -960 -864 -960
WIRE -608 -960 -608 -1008
WIRE -608 -960 -768 -960
WIRE -432 -960 -432 -1008
WIRE -432 -960 -608 -960
WIRE -320 -960 -320 -1168
WIRE -320 -960 -432 -960
WIRE -1120 -912 -1120 -944
WIRE -1040 -912 -1040 -960
WIRE -160 -912 -160 -944
WIRE -1120 -848 -1120 -880
WIRE -1072 -848 -1120 -848
WIRE -1008 -848 -1040 -848
WIRE -944 -848 -976 -848
WIRE -880 -848 -912 -848
WIRE -816 -848 -848 -848
WIRE -752 -848 -784 -848
WIRE -688 -848 -720 -848
WIRE -624 -848 -656 -848
WIRE -560 -848 -592 -848
WIRE -496 -848 -528 -848
WIRE -432 -848 -464 -848
WIRE -368 -848 -400 -848
WIRE -304 -848 -336 -848
WIRE -240 -848 -272 -848
WIRE -160 -848 -160 -880
WIRE -160 -848 -208 -848
WIRE -1168 -784 -1168 -816
WIRE -1120 -784 -1168 -784
FLAG -768 -1232 +12
FLAG -1040 -912 0
FLAG -1040 -1120 +12
FLAG -320 -1248 +12
FLAG -608 -1328 +12
FLAG -240 -1200 KON
FLAG -1696 -1216 0
SYMBOL res -896 -1184 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R3
SYMATTR Value 10K
SYMBOL res -880 -1120 R0
SYMATTR InstName R4
SYMATTR Value 100K
SYMBOL res -720 -1360 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R2
SYMATTR Value 100K
SYMBOL res -896 -1360 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R1
SYMATTR Value 10k
SYMBOL res -1072 -1312 R0
SYMATTR InstName R5
SYMATTR Value 0.1
SYMATTR SpiceLine tol=10 pwr=2
SYMBOL voltage -1056 -1120 R0
WINDOW 0 14 102 Left 2
WINDOW 3 24 96 Invisible 2
WINDOW 123 0 0 Left 2
WINDOW 39 0 0 Left 2
SYMATTR InstName V1
SYMATTR Value 12.2
SYMBOL Opamps\\LT1366 -768 -1248 R0
SYMATTR InstName U1A
SYMBOL Opamps\\LT1366 -320 -1264 R0
SYMATTR InstName U1B
SYMBOL References\\LT1634-5 -608 -1040 R0
WINDOW 3 -96 40 Left 2
WINDOW 0 -64 -1 Left 2
SYMATTR InstName U2
SYMBOL res -464 -1152 R90
WINDOW 0 63 58 VBottom 2
WINDOW 3 67 57 VTop 2
SYMATTR InstName R7
SYMATTR Value 6800
SYMBOL res -448 -1104 R0
WINDOW 3 41 70 Left 2
SYMATTR Value 1000
SYMATTR InstName R8
SYMBOL res -624 -1312 R0
SYMATTR InstName R6
SYMATTR Value 6800
SYMBOL sw -1568 -1184 R0
SYMATTR InstName S1
SYMBOL voltage -1648 -1072 R180
WINDOW 0 24 96 Left 2
WINDOW 3 24 16 Left 2
WINDOW 123 0 0 Left 2
WINDOW 39 0 0 Left 2
SYMATTR InstName V3
SYMATTR Value PULSE(-1 1 0.1 0.01 0.01 3 8 3)
SYMBOL cap -1488 -1264 R0
SYMATTR InstName C1
SYMATTR Value 33000ľf
SYMBOL res -1488 -1360 R0
SYMATTR InstName R10
SYMATTR Value 3.9
SYMBOL res -1648 -1376 R0
SYMATTR InstName R9
SYMATTR Value 4
SYMBOL res -1280 -1312 R0
SYMATTR InstName R11
SYMATTR Value 27
TEXT -1024 -936 Left 2 !.tran 12
TEXT -1088 -792 Left 4 ;CURRENT THRESHOLD DETECTOR
TEXT -416 -872 Left 2 ;J FIELDS 01 JULY 2015
TEXT -1104 -872 Left 3 ;BOARD A
TEXT -1728 -856 Left 2 !.model SW SW()
TEXT -1344 -1200 Left 2 ;LED array (~450ma)
TEXT -1880 -1376 Left 2 ;DC-DC converter, 5v at 2A-5A
TEXT -424 -848 Left 2 ;Crude mods made SMayo

Some notes - I don't know how to model the 400ma LED array as a load, so R11 stands in for that. In reality it's inactive whenever the dc converter is; I just couldn't get a SPDT relay out of spice.

I tweaked R7 to change the triggering current up around 600ma+. It looked like a voltage divider and fair game for adjusting. (In practice: 4.7k + 5k pot)

I don't know how to model a dc-dc converter, so R9 stands in for that. I've made sure the circuit simulates well for resistances between 2 ohms and 300 ohms, on the guess that the converter can't possibly be outside that range.

C1 and R10 are insurance - they cause a current spike when the relay first closes, large enough to guarantee the detector fires even if the converter doesn't draw as much as I think. They cause the detector to fire for at least 50ms, enough for the PIC downstream to see it. If the converter load load is large enough they'll be dropped.

The power supply is from a 12.6Vdc, 4A transformaer, taken through an 8A diode full wave bridge and a largish cap, unregulated.

Questions: if R6, R& and R8 just set the comparison voltage, would a different voltage regulator other than 5V have made sense at U2?

When the dc converter is operational, it's probably going to draw at least 2A at 12v. Is power supply ripple going to be a problem?

TAIA.