Hi everyone,
I’m looking for a simple circuit schematic to make an LED blink for about 1 second every ~5 minutes, powered by a CR2032 battery. The timing doesn’t need to be precise, but Id like to prioritize low power consumption to extend battery life as much as possible.
Thanks for your help!
Thomas

 

Typically, I'd be looking at using a 555 IC but with only 3V you'd be struggling - two CR2032s in series for 6V might be okay. Maybe check out the recent 24 hour timer thread https://forum.allaboutcircuits.com/threads/24-hours-timer.205331/ The TPL5110 IC can be set to trigger every 5 minutes. Use the adafruit break out board. You could use a processor but I don't think it's necessary - when the enable pin triggers to light the LED it could also charge a capacitor through a resistor to generate the "DONE" signal back to the TPL5110.

 

You can try this circuit. Most of the time drains the battery just 330k resistor. The 1k , 470 and Led are active during 1sec interval only.

 

I’m looking for a simple circuit schematic to make an LED blink for about 1 second every ~5 minutes, powered by a CR2032 battery. The timing doesn’t need to be precise, but Id like to prioritize low power consumption to extend battery life as much as possible.

LM3909 LED flasher - if you can find it.

 

During pulse circuit consumes 11 mA, but between pulses 0.0003 mA.


ADDED:
It is better to use ceramic capacitor as C1, for example -
SMD chip Multilayer Ceramic Capacitor 6.3 V, 47 μF.

Time parameters can be adjusted: "5 min" by resistor R4
and "1 sec" by resistor R2.
Brightness of LedRed (and consumed current) may be changed by resistor R3.

 

How close do you need the flash rate to be to 1Hz?

The by far easiest route is self-flashing LEDs.

 

How close do you need the flash rate to be to 1Hz?

Not even close.
He wants 3.33mHz.

 

Not even close.
He wants 3.33mHz.

Oops. I misread the question. But, depending on the purpose of the flashing, these LEDs may offer the best solution in terms of parts count and overall efficiency. At any rate, the poster may not have known about self-flashing LEDs, so the knowledge may be worthwhile.

 

You can try this circuit. Most of the time drains the battery just 330k resistor. The 1k , 470 and Led are active during 1sec interval only.
View attachment 343210

You can probably get away with a larger resistor than 210 Ohms on the LED. The 210 put current at about 13mA. The LED, would likely be bright enough running at 8mA (Resistor: 430 Ohm)

 

Hi everyone,
I’m looking for a simple circuit schematic to make an LED blink for about 1 second every ~5 minutes, powered by a CR2032 battery. The timing doesn’t need to be precise, but Id like to prioritize low power consumption to extend battery life as much as possible.
Thanks for your help!
Thomas

From your description, I see a one-second ON and a 300-second OFF cycle. Is there a reason for the one-second ON? If a flash would work for the same purpose, you can have the LED on for 0.1 seconds and off for 30 seconds, using the same energy as the one-second ON and 300-second OFF cycle. Managing a timing circuit for 30 seconds is more accurate than 300 seconds, resulting in a blinking twice per minute with an on time of only 1/5th of a second.

 

You can try this circuit. Most of the time drains the battery just 330k resistor. The 1k , 470 and Led are active during 1sec interval only.

The thing about this circuit and many like it is that the energy in the main timing capacitor is wasted. The cap is discharged into a resistor while the LED is powered from the rail. The brilliance (!) of the LM3909 is that the timing cap energy is used to light the LED. Somewhere in the past I think I posted a version of how to do this, but ... fog.

ak

 

Oops. I misread the question. But, depending on the purpose of the flashing, these LEDs may offer the best solution in terms of parts count and overall efficiency. At any rate, the poster may not have known about self-flashing LEDs, so the knowledge may be worthwhile.

As mentioned earlier, these blink too often. However, thanks for the info! I wasn’t aware of self-flashing LEDs, so they might be useful for future projects.

 

You can try this circuit. Most of the time drains the battery just 330k resistor. The 1k , 470 and Led are active during 1sec interval only.
View attachment 343210

Ill try it out and let you know. Thanks.

 

During pulse circuit consumes 11 mA, but between pulses 0.0003 mA.
View attachment 343251 View attachment 343260

ADDED:
It is better to use ceramic capacitor as C1, for example -
SMD chip Multilayer Ceramic Capacitor 6.3 V, 47 μF.

Time parameters can be adjusted: "5 min" by resistor R4
and "1 sec" by resistor R2.
Brightness of LedRed (and consumed current) may be changed by resistor R3.

Ill try it out and let you know. Thanks.

 

Is there a reason for the one-second ON?

Yes, seems unnecessarily long.
Changing R4 to 15Ω give about a 100ms pulse.

 

"flash" is a loade word. Hz and duty cycle are more appropriate.

You can overdrive an LED if the duty cycle is low enough, without damage to LED.

Does the ask presume 50% duty cycle, or is it something else?

 

Implementing this with an ATTiny85 MCU using the WDT (Watchdog Timer) and sleep mode, with the clock at 128KHz should run a 1sec/hour 20mA LED for more than 2 years for a CR2032.

 

I was going to suggest basically the same circuit but Danko beat me to it.
Current draw is 0.1 μA.

 

To add to my original post, I run a charity, and we’ve launched a campaign where all local restaurants and cafés have a "shaker" (see image) with a QR code in the back. Scanning it takes you to our website, where people can learn about our work and, ideally, make a donation.
Once people notice the shaker, it has been quite successful. However, many don’t actually see it on the table, as it competes visually with the menu, napkin holder, tabletop specials, and other promotions. One restaurant owner suggested adding a subtle "flash" to draw attention without being disruptive.
So having this in mind, precision isn’t a concern, but brightness is key. Size is also a constraint—I can carve out a 1-inch diameter space inside the cork. Battery efficiency is important as well. After reconsidering, a 5-minute interval seems too frequent; a 30-minute gap between flashes might be better, aiming for one or two flashes during a meal.
Thanks you all for your input and I regret not having given you more context form the start.

Thomas

 

After reconsidering, a 5-minute interval seems too frequent; a 30-minute gap between flashes might be better, aiming for one or two flashes during a meal.

Most certainly you're allowed to build it as you see fit. It's an opinion here, but once every 30 minutes makes it easy to miss. However, in this scenario might I suggest for consideration having it flash ON half a second, OFF half a second, ON half a second, OFF half a second, ON half a second, OFF half a second, ON half a second, OFF half a second, ON half a second, OFF half a second, then go quiet for 15 minutes. Having multiple flashes may draw the wanted attention but having it not occur for every 15 minutes gives a diner time to relax and engage in conversation. Having it flash five times gives the diner time to see it and recognize that it's begging for attention.

In the end you have to decide on exactly how you want your project to perform. As for space, you might consider building - or having a custom cabinet shop build several small platters where your QR code can be and having whatever condiments on it. That way the user is not picking up your flashing device. Though likely rare, I can see some kid being enamored with it and taking it home.

I see them all the time whenever I go to a restaurant, those wire baskets with Salt, Pepper, Sugar, Ketchup or whatever else they may put on it. Then you can take it to any restaurant you like (with permission) and place it on their tables. In other words it's expandable.

Look for a PM from me.