Q: how find specific LED

On Thu, 12 Mar 2020 22:15:54 -0700, Robert Baer
<robertbaer@localnet.com> wrote:

bulegoge@columbus.rr.com wrote:

The idea is to have a battery monitor light that will not unduly run
down the battery.

How about blinking the LED at 25 percent duty cycle...or even lower

A 2.2Meg resistor takes no extra electronic fluff, and at 24V supply
the 10uA is very close to zero load.
Click to expand...

I was thinking, a while back, about some sort of oscillator to make an
LED blink visibly from very low average current. My application was to
minimally load a high voltage supply but warn of voltage present. I
didn't come up with anything profound.

It's an interesting problem. One possibility is to have a ground-based
clock tease an equivalent schmitt once in a while, so it doesn't use
the current it would otherwise take to fire. But that needs a
sustained low voltage supply!




--

John Larkin Highland Technology, Inc
picosecond timing precision measurement

jlarkin att highlandtechnology dott com
http://www.highlandtechnology.com
 
On Friday, March 13, 2020 at 1:05:56 PM UTC-4, John Larkin wrote:
On Thu, 12 Mar 2020 22:15:54 -0700, Robert Baer
robertbaer@localnet.com> wrote:

bulegoge@columbus.rr.com wrote:

The idea is to have a battery monitor light that will not unduly run
down the battery.

How about blinking the LED at 25 percent duty cycle...or even lower

A 2.2Meg resistor takes no extra electronic fluff, and at 24V supply
the 10uA is very close to zero load.

I was thinking, a while back, about some sort of oscillator to make an
LED blink visibly from very low average current. My application was to
minimally load a high voltage supply but warn of voltage present. I
didn't come up with anything profound.

It's an interesting problem. One possibility is to have a ground-based
clock tease an equivalent schmitt once in a while, so it doesn't use
the current it would otherwise take to fire. But that needs a
sustained low voltage supply!
Click to expand...

I don't know about the high voltage, but the idea of being current/energy efficient and providing a low duty cycle would be ideal for a unijunction transistor. The capacitor charges up at a low current, then when reaching the trigger level the cap and additional current is dumped into the LED. Nothing is wasted.

I believe an SCR can be used to create a similar circuit. The only real issue is the mismatch between the low LED voltage and the power supply voltage. Adding a dropping resistor loses a lot of energy. Maybe a circuit to chop the voltage and use a capacitive dropper is the way to go.

--

Rick C.

- Get 1,000 miles of free Supercharging
- Tesla referral code - https://ts.la/richard11209
 
John Larkin wrote:
On Thu, 12 Mar 2020 22:15:54 -0700, Robert Baer
robertbaer@localnet.com> wrote:

bulegoge@columbus.rr.com wrote:

The idea is to have a battery monitor light that will not unduly run
down the battery.

How about blinking the LED at 25 percent duty cycle...or even lower

A 2.2Meg resistor takes no extra electronic fluff, and at 24V supply
the 10uA is very close to zero load.

I was thinking, a while back, about some sort of oscillator to make an
LED blink visibly from very low average current. My application was to
minimally load a high voltage supply but warn of voltage present. I
didn't come up with anything profound.

It's an interesting problem. One possibility is to have a ground-based
clock tease an equivalent schmitt once in a while, so it doesn't use
the current it would otherwise take to fire. But that needs a
sustained low voltage supply!
Click to expand...
Haven't tried this, but might be useful for that application:
Use a STN0214 in a modified joule thief circuit; add a capacitor
between the base and emitter to extend the off time.
 
DecadentLinuxUserNumeroUno@decadence.org wrote:
Robert Baer <robertbaer@localnet.com> wrote in
news:lGEaG.362476$Mj1.242991@fx39.iad:

bulegoge@columbus.rr.com wrote:

The idea is to have a battery monitor light that will not
unduly run
down the battery.

How about blinking the LED at 25 percent duty cycle...or even
lower

A 2.2Meg resistor takes no extra electronic fluff, and at 24V
supply
the 10uA is very close to zero load.


Also unable to illuminate the LED. D'OH!
Click to expand...
* The LED is rather visible, even down to 5uA; did not check at lower
currents.

Use the RIGHT current limit resistor and use THIN PWM 'on' pulses
to make for 'dim' operation.
Click to expand...
 
On Sat, 14 Mar 2020 01:08:00 -0700, Robert Baer
<robertbaer@localnet.com> wrote:

John Larkin wrote:
On Thu, 12 Mar 2020 22:15:54 -0700, Robert Baer
robertbaer@localnet.com> wrote:

bulegoge@columbus.rr.com wrote:

The idea is to have a battery monitor light that will not unduly run
down the battery.

How about blinking the LED at 25 percent duty cycle...or even lower

A 2.2Meg resistor takes no extra electronic fluff, and at 24V supply
the 10uA is very close to zero load.

I was thinking, a while back, about some sort of oscillator to make an
LED blink visibly from very low average current. My application was to
minimally load a high voltage supply but warn of voltage present. I
didn't come up with anything profound.

It's an interesting problem. One possibility is to have a ground-based
clock tease an equivalent schmitt once in a while, so it doesn't use
the current it would otherwise take to fire. But that needs a
sustained low voltage supply!




Haven't tried this, but might be useful for that application:
Use a STN0214 in a modified joule thief circuit; add a capacitor
between the base and emitter to extend the off time.
Click to expand...

The issue becomes, how much base current does it need to fire?
Possibly nanoamps.

And how much average power does a good LED need to be a visible
blinking warning? 100 uW? That would, in an ideal world, need 100 nA
from a kilovolt power supply.



--

John Larkin Highland Technology, Inc

The cork popped merrily, and Lord Peter rose to his feet.
"Bunter", he said, "I give you a toast. The triumph of Instinct over Reason"
 
https://en.wikipedia.org/wiki/Pulse_(Pink_Floyd_album)

my suggestion is an avalanche transistor))
 
jlarkin@highlandsniptechnology.com wrote:
On Sat, 14 Mar 2020 01:08:00 -0700, Robert Baer
robertbaer@localnet.com> wrote:

John Larkin wrote:
On Thu, 12 Mar 2020 22:15:54 -0700, Robert Baer
robertbaer@localnet.com> wrote:

bulegoge@columbus.rr.com wrote:

The idea is to have a battery monitor light that will not unduly run
down the battery.

How about blinking the LED at 25 percent duty cycle...or even lower

A 2.2Meg resistor takes no extra electronic fluff, and at 24V supply
the 10uA is very close to zero load.

I was thinking, a while back, about some sort of oscillator to make an
LED blink visibly from very low average current. My application was to
minimally load a high voltage supply but warn of voltage present. I
didn't come up with anything profound.

It's an interesting problem. One possibility is to have a ground-based
clock tease an equivalent schmitt once in a while, so it doesn't use
the current it would otherwise take to fire. But that needs a
sustained low voltage supply!




Haven't tried this, but might be useful for that application:
Use a STN0214 in a modified joule thief circuit; add a capacitor
between the base and emitter to extend the off time.

The issue becomes, how much base current does it need to fire?
Possibly nanoamps.
* Most definitely.
Click to expand...

And how much average power does a good LED need to be a visible
blinking warning? 100 uW? That would, in an ideal world, need 100 nA
from a kilovolt power supply.
Click to expand...
Define "good"; the CREE LEDs seem to be able to approach that ideal
(see my info previously posted).
Also, what would one like for "visible"? The eye sees light pulses
apparently as well as if LED was on constantly; rather helpful in this app.
So, maybe a pulse of 250uA every second could keep the power drain
down and still show existence of HV; rather bright for he CREE LED.

Thanks
 
Robert Baer wrote:
DecadentLinuxUserNumeroUno@decadence.org wrote:
Robert Baer <robertbaer@localnet.com> wrote in
news:lGEaG.362476$Mj1.242991@fx39.iad:

bulegoge@columbus.rr.com wrote:

     The idea is to have a battery monitor light that will not
     unduly run
down the battery.

How about blinking the LED at 25 percent duty cycle...or even
lower

    A 2.2Meg resistor takes no extra electronic fluff, and at 24V
    supply
the 10uA is very close to zero load.


   Also unable to illuminate the LED.  D'OH!
* The LED is rather visible, even down to 5uA; did not check at lower
currents.


   Use the RIGHT current limit resistor and use THIN PWM 'on' pulses
to make for 'dim' operation.
Click to expand...
The CREE C503B-RBS-CY0Z0AA1 (standard LED) is definitely visible (in
relatively dark room) at 0.16uA, supply 4.95V, 22 Meg resistor in series.
That calculates to 1.43V across the LED!

One wonders what one of their "better" high intensity LEDs would
perform...
 
On Wednesday, March 18, 2020 at 2:09:04 AM UTC-4, Robert Baer wrote:
jlarkin@highlandsniptechnology.com wrote:
On Sat, 14 Mar 2020 01:08:00 -0700, Robert Baer
robertbaer@localnet.com> wrote:

John Larkin wrote:
On Thu, 12 Mar 2020 22:15:54 -0700, Robert Baer
robertbaer@localnet.com> wrote:

bulegoge@columbus.rr.com wrote:

The idea is to have a battery monitor light that will not unduly run
down the battery.

How about blinking the LED at 25 percent duty cycle...or even lower

A 2.2Meg resistor takes no extra electronic fluff, and at 24V supply
the 10uA is very close to zero load.

I was thinking, a while back, about some sort of oscillator to make an
LED blink visibly from very low average current. My application was to
minimally load a high voltage supply but warn of voltage present. I
didn't come up with anything profound.

It's an interesting problem. One possibility is to have a ground-based
clock tease an equivalent schmitt once in a while, so it doesn't use
the current it would otherwise take to fire. But that needs a
sustained low voltage supply!




Haven't tried this, but might be useful for that application:
Use a STN0214 in a modified joule thief circuit; add a capacitor
between the base and emitter to extend the off time.

The issue becomes, how much base current does it need to fire?
Possibly nanoamps.
* Most definitely.


And how much average power does a good LED need to be a visible
blinking warning? 100 uW? That would, in an ideal world, need 100 nA
from a kilovolt power supply.



Define "good"; the CREE LEDs seem to be able to approach that ideal
(see my info previously posted).
Also, what would one like for "visible"? The eye sees light pulses
apparently as well as if LED was on constantly; rather helpful in this app.
Click to expand...

I'm not sure why you say that. Many car tail lights blink the LEDs rather than dim the current between tail light and brake light modes. I know this for a fact because I can see it when I turn my eyes. I find it very distracting and annoying.

--

Rick C.

+ Get 1,000 miles of free Supercharging
+ Tesla referral code - https://ts.la/richard11209
 
On Wednesday, March 18, 2020 at 2:26:19 AM UTC-4, Rick C wrote:

When my post actually loads...
We're using those same CREE LED's in the project (about 16 of them), all driven at around 710 uA.

(...and I might have to reduce them a bit more)
But, plenty bright at 710 uA. (Both red and green types.)
 
On Wednesday, March 18, 2020 at 2:26:19 AM UTC-4, Rick C wrote:
> I'm not sure why you say that. Many car tail lights blink the LEDs rather than dim the current between tail light and brake light modes. I know this for a fact because I can see it when I turn my eyes. I find it very distracting and annoying.

I'm working on a rather large project right now where I will have to blink the LED's in order to meet the power budget. If that were all I had to do, then OK.

But Nooooooo. (That would be too easy!)

I'm also going to have to tri-state most of the port pins when not actively using them, constantly switch to the low-power internal oscillator (with clock dividers active) during time-insensitive subroutines, use idle mode, use power-down mode, use external FET's to control things like resistive port pull-ups, and tweak the hell out of the code to do as much as possible with as few clock cycles as possible. Every FET is very low RdS, and regulators are high-speed switchers and LDO's, with on/off control. And of course, all the relays are dual-coil latching types, so it messes with your head a little trying to keep track of their states. (Not difficult, just can be confusing.)

In short: The "Full Monty" of tricks.

If I could have about 10-15 mW more in the budget, I could probably ditch about 2/3rd of these complications! OK, maybe 20. :)

Unfortunately, the lead-acid battery is the determining factor (both capacity and physical size, and I guess re-charge time - though that is not spec'd), so I'm stuck.
 
On Tue, 17 Mar 2020 23:08:53 -0700, Robert Baer
<robertbaer@localnet.com> wrote:

jlarkin@highlandsniptechnology.com wrote:
On Sat, 14 Mar 2020 01:08:00 -0700, Robert Baer
robertbaer@localnet.com> wrote:

John Larkin wrote:
On Thu, 12 Mar 2020 22:15:54 -0700, Robert Baer
robertbaer@localnet.com> wrote:

bulegoge@columbus.rr.com wrote:

The idea is to have a battery monitor light that will not unduly run
down the battery.

How about blinking the LED at 25 percent duty cycle...or even lower

A 2.2Meg resistor takes no extra electronic fluff, and at 24V supply
the 10uA is very close to zero load.

I was thinking, a while back, about some sort of oscillator to make an
LED blink visibly from very low average current. My application was to
minimally load a high voltage supply but warn of voltage present. I
didn't come up with anything profound.

It's an interesting problem. One possibility is to have a ground-based
clock tease an equivalent schmitt once in a while, so it doesn't use
the current it would otherwise take to fire. But that needs a
sustained low voltage supply!




Haven't tried this, but might be useful for that application:
Use a STN0214 in a modified joule thief circuit; add a capacitor
between the base and emitter to extend the off time.

The issue becomes, how much base current does it need to fire?
Possibly nanoamps.
* Most definitely.


And how much average power does a good LED need to be a visible
blinking warning? 100 uW? That would, in an ideal world, need 100 nA
from a kilovolt power supply.



Define "good"; the CREE LEDs seem to be able to approach that ideal
(see my info previously posted).
Also, what would one like for "visible"? The eye sees light pulses
apparently as well as if LED was on constantly; rather helpful in this app.
So, maybe a pulse of 250uA every second could keep the power drain
down and still show existence of HV; rather bright for he CREE LED.

Thanks
Click to expand...

I wonder how low a supply current could be achieved with the classic
2-transistor (or mosfet) astable multivibrator. Nanoamps? I guess that
could be Spiced, given a proper mosfet model.

There may be an SCR/PUT type configuration with mosfets, or even
bipolars, that would fire at very low currents.



--

John Larkin Highland Technology, Inc

The cork popped merrily, and Lord Peter rose to his feet.
"Bunter", he said, "I give you a toast. The triumph of Instinct over Reason"
 
On Wednesday, March 18, 2020 at 7:52:57 AM UTC-4, mpm wrote:
On Wednesday, March 18, 2020 at 2:26:19 AM UTC-4, Rick C wrote:
I'm not sure why you say that. Many car tail lights blink the LEDs rather than dim the current between tail light and brake light modes. I know this for a fact because I can see it when I turn my eyes. I find it very distracting and annoying.

I'm working on a rather large project right now where I will have to blink the LED's in order to meet the power budget. If that were all I had to do, then OK.
Click to expand...

How does blinking the LED reduce power consumption compared to reducing the current? Seems to me it is a constant power/energy situation when taking into account the power/energy in the current limiting.

--

Rick C.

-- Get 1,000 miles of free Supercharging
-- Tesla referral code - https://ts.la/richard11209
 
On Wed, 18 Mar 2020 04:52:50 -0700 (PDT), mpm <mpmillard@aol.com>
wrote:

On Wednesday, March 18, 2020 at 2:26:19 AM UTC-4, Rick C wrote:
I'm not sure why you say that. Many car tail lights blink the LEDs rather than dim the current between tail light and brake light modes. I know this for a fact because I can see it when I turn my eyes. I find it very distracting and annoying.

I'm working on a rather large project right now where I will have to blink the LED's in order to meet the power budget. If that were all I had to do, then OK.

But Nooooooo. (That would be too easy!)

I'm also going to have to tri-state most of the port pins when not actively using them, constantly switch to the low-power internal oscillator (with clock dividers active) during time-insensitive subroutines, use idle mode, use power-down mode, use external FET's to control things like resistive port pull-ups, and tweak the hell out of the code to do as much as possible with as few clock cycles as possible. Every FET is very low RdS, and regulators are high-speed switchers and LDO's, with on/off control. And of course, all the relays are dual-coil latching types, so it messes with your head a little trying to keep track of their states. (Not difficult, just can be confusing.)
Click to expand...

Since you are talking about latching relays, it sounds like sometimes
some high power will flow through your device. Why not steal some
power from that circuit to power the ON indicators ?

Regarding knowing the state of a latching relay, decades ago I made an
optoisolator consisting of a neon lamp on the mains side and a photo
Darlington feeding some CMOS logic.

You could use two neon lamps on the high power side (possibly both in
series for 230 Vac and above) and use one for the feedback and the
other as an ON indicator. With a very low current LED, you could even
put it in series with the neon lamp. If neon lamps are out of the
question and the high power is AC, you could use a capacitive voltage
divider to feed an ordinary LED optoisolator and indicator LED.

In short: The "Full Monty" of tricks.

If I could have about 10-15 mW more in the budget, I could probably ditch about 2/3rd of these complications! OK, maybe 20. :)

Unfortunately, the lead-acid battery is the determining factor (both capacity and physical size, and I guess re-charge time - though that is not spec'd), so I'm stuck.
Click to expand...
 
On Tue, 17 Mar 2020 23:08:53 -0700, Robert Baer
<robertbaer@localnet.com> wrote:

jlarkin@highlandsniptechnology.com wrote:
On Sat, 14 Mar 2020 01:08:00 -0700, Robert Baer
robertbaer@localnet.com> wrote:

John Larkin wrote:
On Thu, 12 Mar 2020 22:15:54 -0700, Robert Baer
robertbaer@localnet.com> wrote:

bulegoge@columbus.rr.com wrote:

The idea is to have a battery monitor light that will not unduly run
down the battery.

How about blinking the LED at 25 percent duty cycle...or even lower

A 2.2Meg resistor takes no extra electronic fluff, and at 24V supply
the 10uA is very close to zero load.

I was thinking, a while back, about some sort of oscillator to make an
LED blink visibly from very low average current. My application was to
minimally load a high voltage supply but warn of voltage present. I
didn't come up with anything profound.

It's an interesting problem. One possibility is to have a ground-based
clock tease an equivalent schmitt once in a while, so it doesn't use
the current it would otherwise take to fire. But that needs a
sustained low voltage supply!




Haven't tried this, but might be useful for that application:
Use a STN0214 in a modified joule thief circuit; add a capacitor
between the base and emitter to extend the off time.

The issue becomes, how much base current does it need to fire?
Possibly nanoamps.
* Most definitely.


And how much average power does a good LED need to be a visible
blinking warning? 100 uW? That would, in an ideal world, need 100 nA
from a kilovolt power supply.



Define "good";
Click to expand...

A good LED puts out more visible light per mA than a bad one.



--

John Larkin Highland Technology, Inc

The cork popped merrily, and Lord Peter rose to his feet.
"Bunter", he said, "I give you a toast. The triumph of Instinct over Reason"
 
On 18/03/2020 15:29, Rick C wrote:
On Wednesday, March 18, 2020 at 7:52:57 AM UTC-4, mpm wrote:
On Wednesday, March 18, 2020 at 2:26:19 AM UTC-4, Rick C wrote:
I'm not sure why you say that. Many car tail lights blink the
LEDs rather than dim the current between tail light and brake
light modes. I know this for a fact because I can see it when I
turn my eyes. I find it very distracting and annoying.

I'm working on a rather large project right now where I will have
to blink the LED's in order to meet the power budget. If that were
all I had to do, then OK.

How does blinking the LED reduce power consumption compared to
reducing the current? Seems to me it is a constant power/energy
situation when taking into account the power/energy in the current
limiting.
Click to expand...

Blinking an LED fast ( > 100 Hz) but not too fast can give an impression
of higher brightness to the human eye than you'd get with regulating the
current. I haven't confirmed this in detail, but I have heard somewhere
that a 20% duty cycle at, say, 200 Hz gives the equivalent apparent
brightness of 100% duty cycle with half the current.
 
On Wednesday, March 18, 2020 at 11:41:16 AM UTC-4, David Brown wrote:
On 18/03/2020 15:29, Rick C wrote:
On Wednesday, March 18, 2020 at 7:52:57 AM UTC-4, mpm wrote:
On Wednesday, March 18, 2020 at 2:26:19 AM UTC-4, Rick C wrote:
I'm not sure why you say that. Many car tail lights blink the
LEDs rather than dim the current between tail light and brake
light modes. I know this for a fact because I can see it when I
turn my eyes. I find it very distracting and annoying.

I'm working on a rather large project right now where I will have
to blink the LED's in order to meet the power budget. If that were
all I had to do, then OK.

How does blinking the LED reduce power consumption compared to
reducing the current? Seems to me it is a constant power/energy
situation when taking into account the power/energy in the current
limiting.


Blinking an LED fast ( > 100 Hz) but not too fast can give an impression
of higher brightness to the human eye than you'd get with regulating the
current. I haven't confirmed this in detail, but I have heard somewhere
that a 20% duty cycle at, say, 200 Hz gives the equivalent apparent
brightness of 100% duty cycle with half the current.
Click to expand...

So no reference???

I screwed up a board design using resistors that were too small and the LEDs were quite bright. I dimmed them by duty cycle modulating at about 20%. I think it was faster than 200 Hz, but still... I would find this a hard concept to believe unless there is a reference somewhere. I can't think of a mechanism in the eye that would provide for perceived brightness being the same on a duty cycled light but only if the flash rate were in some specific, small range.

In fact, as contrary information, the tail lights of autos are often dimmed exactly this way, but pulsing them. I find it immensely irritating when I see a dozen tail lights as I move swing my view across the road in front of me. I expect this flash rate is somewhere around 100-1000 Hz and is being done specifically to dim the lights.

So the more I think about it, the less I am inclined to believe there is any such effect making a blinking LED appear relatively brighter than a solidly on LED at the same power levels. In fact, there should be some effect, even if small, reducing the relative brightness at high current levels.

Do you have any references other than "I have heard somewhere"?

--

Rick C.

-+ Get 2,000 miles of free Supercharging
-+ Tesla referral code - https://ts.la/richard11209
 
jlarkin@highlandsniptechnology.com wrote:
On Tue, 17 Mar 2020 23:08:53 -0700, Robert Baer
robertbaer@localnet.com> wrote:

jlarkin@highlandsniptechnology.com wrote:
On Sat, 14 Mar 2020 01:08:00 -0700, Robert Baer
robertbaer@localnet.com> wrote:

John Larkin wrote:
On Thu, 12 Mar 2020 22:15:54 -0700, Robert Baer
robertbaer@localnet.com> wrote:

bulegoge@columbus.rr.com wrote:

The idea is to have a battery monitor light that will not unduly run
down the battery.

How about blinking the LED at 25 percent duty cycle...or even lower

A 2.2Meg resistor takes no extra electronic fluff, and at 24V supply
the 10uA is very close to zero load.

I was thinking, a while back, about some sort of oscillator to make an
LED blink visibly from very low average current. My application was to
minimally load a high voltage supply but warn of voltage present. I
didn't come up with anything profound.

It's an interesting problem. One possibility is to have a ground-based
clock tease an equivalent schmitt once in a while, so it doesn't use
the current it would otherwise take to fire. But that needs a
sustained low voltage supply!




Haven't tried this, but might be useful for that application:
Use a STN0214 in a modified joule thief circuit; add a capacitor
between the base and emitter to extend the off time.

The issue becomes, how much base current does it need to fire?
Possibly nanoamps.
* Most definitely.


And how much average power does a good LED need to be a visible
blinking warning? 100 uW? That would, in an ideal world, need 100 nA
from a kilovolt power supply.



Define "good"; the CREE LEDs seem to be able to approach that ideal
(see my info previously posted).
Also, what would one like for "visible"? The eye sees light pulses
apparently as well as if LED was on constantly; rather helpful in this app.
So, maybe a pulse of 250uA every second could keep the power drain
down and still show existence of HV; rather bright for he CREE LED.

Thanks

I wonder how low a supply current could be achieved with the classic
2-transistor (or mosfet) astable multivibrator. Nanoamps? I guess that
could be Spiced, given a proper mosfet model.

There may be an SCR/PUT type configuration with mosfets, or even
bipolars, that would fire at very low currents.
Click to expand...
I think that 100nA for bipolars in a multivibrator would give a very
stable and repeatable operation; besides, 100nA will nicely light up a
CREE LED.
 
On Wed, 18 Mar 2020 13:42:51 -0700, Robert Baer
<robertbaer@localnet.com> wrote:

jlarkin@highlandsniptechnology.com wrote:
On Tue, 17 Mar 2020 23:08:53 -0700, Robert Baer
robertbaer@localnet.com> wrote:

jlarkin@highlandsniptechnology.com wrote:
On Sat, 14 Mar 2020 01:08:00 -0700, Robert Baer
robertbaer@localnet.com> wrote:

John Larkin wrote:
On Thu, 12 Mar 2020 22:15:54 -0700, Robert Baer
robertbaer@localnet.com> wrote:

bulegoge@columbus.rr.com wrote:

The idea is to have a battery monitor light that will not unduly run
down the battery.

How about blinking the LED at 25 percent duty cycle...or even lower

A 2.2Meg resistor takes no extra electronic fluff, and at 24V supply
the 10uA is very close to zero load.

I was thinking, a while back, about some sort of oscillator to make an
LED blink visibly from very low average current. My application was to
minimally load a high voltage supply but warn of voltage present. I
didn't come up with anything profound.

It's an interesting problem. One possibility is to have a ground-based
clock tease an equivalent schmitt once in a while, so it doesn't use
the current it would otherwise take to fire. But that needs a
sustained low voltage supply!




Haven't tried this, but might be useful for that application:
Use a STN0214 in a modified joule thief circuit; add a capacitor
between the base and emitter to extend the off time.

The issue becomes, how much base current does it need to fire?
Possibly nanoamps.
* Most definitely.


And how much average power does a good LED need to be a visible
blinking warning? 100 uW? That would, in an ideal world, need 100 nA
from a kilovolt power supply.



Define "good"; the CREE LEDs seem to be able to approach that ideal
(see my info previously posted).
Also, what would one like for "visible"? The eye sees light pulses
apparently as well as if LED was on constantly; rather helpful in this app.
So, maybe a pulse of 250uA every second could keep the power drain
down and still show existence of HV; rather bright for he CREE LED.

Thanks

I wonder how low a supply current could be achieved with the classic
2-transistor (or mosfet) astable multivibrator. Nanoamps? I guess that
could be Spiced, given a proper mosfet model.

There may be an SCR/PUT type configuration with mosfets, or even
bipolars, that would fire at very low currents.



I think that 100nA for bipolars in a multivibrator would give a very
stable and repeatable operation; besides, 100nA will nicely light up a
CREE LED.
Click to expand...

My HV warning problem would blink the LED pretty bright, at 1 Hz
maybe. All sorts of wild LED pulsers are possible, but I wanted to
make the basic 1 Hz oscillator use very little current.

We could experiment. I'm guessing a 50 millisecond light pulse, maybe
a bit less, would be a good investment in current.



--

John Larkin Highland Technology, Inc

The cork popped merrily, and Lord Peter rose to his feet.
"Bunter", he said, "I give you a toast. The triumph of Instinct over Reason"
 
On 18/03/2020 17:36, Rick C wrote:
On Wednesday, March 18, 2020 at 11:41:16 AM UTC-4, David Brown
wrote:
On 18/03/2020 15:29, Rick C wrote:
On Wednesday, March 18, 2020 at 7:52:57 AM UTC-4, mpm wrote:
On Wednesday, March 18, 2020 at 2:26:19 AM UTC-4, Rick C
wrote:
I'm not sure why you say that. Many car tail lights blink
the LEDs rather than dim the current between tail light and
brake light modes. I know this for a fact because I can see
it when I turn my eyes. I find it very distracting and
annoying.

I'm working on a rather large project right now where I will
have to blink the LED's in order to meet the power budget. If
that were all I had to do, then OK.

How does blinking the LED reduce power consumption compared to
reducing the current? Seems to me it is a constant power/energy
situation when taking into account the power/energy in the
current limiting.


Blinking an LED fast ( > 100 Hz) but not too fast can give an
impression of higher brightness to the human eye than you'd get
with regulating the current. I haven't confirmed this in detail,
but I have heard somewhere that a 20% duty cycle at, say, 200 Hz
gives the equivalent apparent brightness of 100% duty cycle with
half the current.

So no reference???
Click to expand...

I might try to find one if I get the chance. But it is certainly a
common technique.

I screwed up a board design using resistors that were too small and
the LEDs were quite bright. I dimmed them by duty cycle modulating
at about 20%. I think it was faster than 200 Hz, but still... I
would find this a hard concept to believe unless there is a reference
somewhere. I can't think of a mechanism in the eye that would
provide for perceived brightness being the same on a duty cycled
light but only if the flash rate were in some specific, small range.
Click to expand...

The retina cells react stronger to a change in light intensity. So the
initial part of the flash causes a stronger reaction than later parts.
Thus the blinking looks brighter. But if the blinking is too fast, the
cells don't have the time to "reset" between on-times, reducing the
effect. The effect is biggest with slower blinking (though the higher
level processing in the brain, which emphasises changes and movement,
has a bigger contribution for very slow blinking - that's why bike
lights often blink, as I'm sure you know). But below about 100 Hz and
you can see the flickering if you move your eyes, and that gets annoying.

In fact, as contrary information, the tail lights of autos are often
dimmed exactly this way, but pulsing them. I find it immensely
irritating when I see a dozen tail lights as I move swing my view
across the road in front of me. I expect this flash rate is
somewhere around 100-1000 Hz and is being done specifically to dim
the lights.
Click to expand...

Of course you dim them that way - it is the simplest and most efficient
method. You just have to reduce the duty cycle more than you would
otherwise expect from a simple linear calculation.

So the more I think about it, the less I am inclined to believe there
is any such effect making a blinking LED appear relatively brighter
than a solidly on LED at the same power levels. In fact, there
should be some effect, even if small, reducing the relative
brightness at high current levels.

Do you have any references other than "I have heard somewhere"?
Click to expand...

Real life practice.

I can't claim to have done any measurements or scientific comparisons,
however.
 
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