Powering pro mini with A23 12V alkaline battery on RAW

Hello,

My sketch is very simple, just a timer having two pushbuttons and one buzzer. It works fine when pro mini is connected to usb/serial converter. But powered by a A23 12V alcaline battery, (in RAW) a led near pins 8 and 9, after a while, starts to blink fast and the program crashes. Any clue about what is going wrong?

The most likely explanation is the regulator chip is overheating. It may even be hot to the touch.

While the regulator is rated to handle the 12V, the heat generated is a function of the voltage drop across the regulator and the current used by the load. Presumably the current is the same no matter where you source from, but the voltage drop down to 3.3V or 5V is quite high with 12V coming in. In fact you are simply wasting most of your battery power as heat.

You might try a 9V battery instead, and/or if possible source the power for things like LEDs and buzzers directly from RAW so the regulator doesn't have to carry that current at all, with the processor driving transistors that control those devices.

The other possibility is the regulator is defective. Since powering from the serial adapter completely bypasses the regulator, a problem there wouldn't show up. But really the most likely answer is that everything is working fine, but your 12V input voltage is just too great for the current you're using.

Thanks for your answer. I will try to power it differently. But I am still intrigued by the onboard red LED that blinks before the pro mini collapses. Is that a sort of alarm? It is positioned right near the pins 8 and 9. Do you know what it is?

lungovw:
Thanks for your answer. I will try to power it differently. But I am still intrigued by the onboard red LED that blinks before the pro mini collapses. Is that a sort of alarm? It is positioned right near the pins 8 and 9. Do you know what it is?

The schematic for the pro mini shows one red LED, and that's the "power on" LED. It just comes off the regulator output, so there's no logic controlling it. I suspect it is turning off and back on because the voltage coming out of the regulator is fluctuating - possibly some kind of cycling thermal limiting. That LED should be on solid when you power from the USB adapter.

I don’t want to look stubborn, but the blinking LED I meant is a different one. It is located between pin D9 and reset button. In my case it is normally off and then it blinks very fast a few seconds and the Pro Mini crashes. I wish I could upload an image over here to show you but it seems it is not possible. Unfortunatelly I don’t know how to read the schematic you sent. Thanks for your help and attention anyway. I will try to power it with 2 lithium button 3V batteries on raw. I have no room for 3 AAA or 9V battery as I fit it in a very small box. I will check first it it works and second how long it lasts. It is intended to be a timer for analog photography to be used in a darkroom.

I would suspect that those batteries are not capable of supplying the current needed by the Arduino for any length of time. They’re designed for very low power (essentially, 8 watch batteries in series), and while the Arduino isn’t really a high-power device, its 10 to 50mA is probably more than the battery can take.

The blinking LED could be a series of brownout resets - voltage droops, arduino resets. Current drawn during reset is lower, battery voltage recovers, arduino restarts. Repeat…

westfw, I think you are right. I checked and the A23 battery can handle only 55 mA. Thanks for your input. I didn't want a cable, but I set an external 5V power supply and now it is running smoothly.