Add a low power indicator LED

Get the mouser app from Google play and search for leds.

What you want is a high efficiency LED. Typical LED currents are 10-20 mA which is too much for a battery powered application. You need to find one with a much smaller nominal current and further reduce the average current by turning it on with a 10% duty cycle, taking advantage of the LED's persistence.

Use a color that has max eye sensitivity also helps :





Regards, Dana.

As noted, find a high-brightness LED with a low current requirement and run it on just enough current to make it visible.

The eye is most sensitive to color in the yellow part of the spectrum.

You can use a simple astable circuit to pulse the LED at a low frequency to further reduce its power requirements.

crutschow said:

As noted, find a high-brightness LED with a low current requirement and run it on just enough current to make it visible.

The eye is most sensitive to color in the yellow part of the spectrum.

You can use a simple astable circuit to pulse the LED at a low frequency to further reduce its power requirements.

Click to expand...

Or simply use the Arduino to flash it - using a timer interrupt to wake up from sleep (it may already be doing this?).

Many of my projects 'run' in sleep, and wake up every second (or less), it's easy to flash an LED for as long as you want as often as you want.

Spectral response eye -



Regards, Dana.

danadak said:

Spectral response eye

Click to expand...

An interesting LED test would be which color is still visible at the lowest current level, which is influenced by both the eye sensitivity and the LED efficiency.

Regards, Dana.

I got a bunch of these from Tayda. Even with a 10K resistor, and 5V supply, they seem bright enough for me. That's less than 0.5mA.

https://www.taydaelectronics.com/led-3mm-blue-diffuse-lens.html

I changed the thread title.

danadak said:

Use a color that has max eye sensitivity also helps :

View attachment 138099

Ultra low power LED

Use case: baby retrieving its pacifier Young parents don't like to get up three times a night to retrieve baby's pacifier. You could tie a short rope to the pacifier and connect it to the baby's clothes, but some babies always yank those loose. Use case: finding flashlight: When do you need a...

hackaday.io

Regards, Dana.

Click to expand...

Very interesting. While yellow may have max eye sensitivity, in advertising people will choose a red label over a yellow one.

Nigel Goodwin said:

Or simply use the Arduino to flash it - using a timer interrupt to wake up from sleep (it may already be doing this?).

Many of my projects 'run' in sleep, and wake up every second (or less), it's easy to flash an LED for as long as you want as often as you want.

Click to expand...

I thought of perhaps using a 555 timer to flash the LED but it would add components, most likely use more power, and basically cause more problems than it solves.

Maybe using the Arduino itself would be the best choice.

Right now, I am using both pins 2 and 3 for interrupts. How I would go about doing that at the moment I do not know. Is there a write up on this somewhere you may know of? Remember, at this time I have not disabled the Arduino onboard indicator LED.

jack0987 said:

I thought of perhaps using a 555 timer to flash the LED but it would add components, most likely use more power, and basically cause more problems than it solves.

Maybe using the Arduino itself would be the best choice.

Right now, I am using both pins 2 and 3 for interrupts. How I would go about doing that at the moment I do not know. Is there a write up on this somewhere you may know of? Remember, at this time I have not disabled the Arduino onboard indicator LED.

Click to expand...

I use mainly PIC's, but I imagine you can set AVR timers to wake up from sleep, just as you can PIC ones.

Here you go:


It even flashes an LED

Use the watchdog timer if you are using the other timers, and set it
up for interrupt mode, not CPU reset mode.


Google this "avr watchdog timer interrupt mode sleep", a number of hits for help.


Regards, Dana.

Although continuously waking the Arduino and blinking an led every few seconds is a possibility, I fear that method in the end will use more power than just connecting a very small, led directly to the battery and just let it run. Perhaps the very tiny surface mount ones like on the Arduino Mini board will do the trick. I'd like to use a blue one but do not know what to look for.

Could you link me to a part, please.

EDIT: On second thought, maybe having the led light up when the battery needs recharging may be better.

I would have used a simple RED 3mm LED.

jack0987 said:

Although continuously waking the Arduino and blinking an led every few seconds is a possibility, I fear that method in the end will use more power than just connecting a very small, led directly to the battery and just let it run. Perhaps the very tiny surface mount ones like on the Arduino Mini board will do the trick. I'd like to use a blue one but do not know what to look for.

Could you link me to a part, please.

EDIT: On second thought, maybe having the led light up when the battery needs recharging may be better.

Click to expand...

Just use a sample blink sleep program and measure the difference in current drain.

I think you will find its a big difference in current draw, hence battery life.

Note depends on board used, as to what's external; left running.


Regards, Dana.

jack0987 said:

Although continuously waking the Arduino and blinking an led every few seconds is a possibility, I fear that method in the end will use more power than just connecting a very small, led directly to the battery and just let it run.

Click to expand...

How do you work that out? - having the LED ON all the time drawing 1mA (for example) takes 1mA on average. Using the processor to flash the LED with 1mA for a second every ten seconds only averages 100uA, a 90% saving - so the battery will last ten times as long. The power the processor uses is far too small to bother about, as it's in sleep almost all the time, and only wakes for very brief periods.

You also don't need to flash it for as long as 1 second, much shorter is perfectly acceptable, and easily noticeable.

You've got an Arduino?, it has an LED on the board - try flashing that from sleep (consult the link I gave above) and measure the current taken. Experiment with ON/OFF times to see what you consider a good indicator, and then try an external LED, and alter it's series resistor upwards, until you get minimum current with acceptable brightness.

I usually use PIC's, and for longest battery life I use an external 32KHz crystal on TMR1, which wakes the PIC every second - I usually then update the 'real time clock', and check for whatever the device is supposed to be doing, then go back to sleep. This only takes microseconds - and battery life is likely to exceed the shelf life of most batteries - so we use special long shelf life Lithium batteries. Five+ years should be easily doable.

For less critical uses I just use the internal clock, modern PIC's have LOAD'S of clock options, and usually wake the device every millisecond, and keep a millisecond count running, as well as an RTC. Although power consumption is higher than the external 32KHz option, it's still stupidly small