Low-power alternative to Arduino, for simple project

Question

I have a really plain Arduino project: ultra-sonic sensor HC-SR04 returns distance which is then used as sleep time during a LED-wave effect. So it's a simple distance <-> LED-wave velocity relation. The closer you walk towards the device, the faster the LEDs. That's all.

The current being drawn when not running LED-wave and just checking 5 times per second if the distance is lower than 2 meters: 15 mA. This value is in my opinion huge.

I then heard about ESP-8266. It can fully replace Arduino. However the power levels are still not good enough. Browsed more, read about Teensy and others, and they all draw power like a crazy – it appears like this if only a person thinks about using batteries for a moment.

I think that professionals know the solution. Hobbysts are stuck in very fun Arduino world.

Can someone reveal the truth? There must be an answer as e.g. computer mice can run months on two AA. Or, for example, a shopped motion-detection-triggered lamp nicely worked for 7 days before I got bored with it and have put it into drawer. The lamp was giving actual light, not LED blinks, and didn't drain the three AAA batteries it used.

What can I use for my plain project? Need ping functionality for HC-SR04, 8 pins for LEDs and that's all. How to do this correctly and have battery lasting for months?

Answer 1

The Arduino has regulators and USB-Serial chips that are not Sleep friendly.

If you look at the Datasheet for the ATMega328 (section 32.2.2) however you will see that Sleep states exist down to around 4-8 uA (wake on WDT) for the MCU.

Consider simply building your own Arduino clone (if that's the programming environment you want to use) that has only the ATMega328 (or other AVR such as the ATMega8L) on it. You could run from 3 AAA batteries without a regulator at all providing you don't need to support higher voltage LEDs. There are many resources that show how to program an Arduino bootloader environment into a standalone AVR MCU. You could start here and here.

Answer 2

The chip used in the Arduino Uno (Atmega328P) can certainly do low-power.

See my page about power savings for more details.

My base expectation is that if you don't need a timer (eg. to do something periodically) you can get down to 100 nA of current, and still wake on an interrupt, such as a switch press.

If you need to wake from time to time (using the watchdog timer) your current usage will be around 6.5 µA. This is way lower than the 15 mA you quote.

If you use an Arduino board then the on-board LED, the USB interface chip, and the voltage regulator will be the main power culprits. Plus, not going into sleep mode doesn't help.

I made a temperature and humidity logger, see picture below, which has been running now for a couple of years taking a reading every 15 minutes and logging it to an SD card. That runs from 3 x AA batteries.

It is designed to sleep most of the time. The "peripherals power mosfet" shown is used to "power off" the on-board devices when not needed.

Answer 3

I think I've found the answer: Texas Instruments' MCUs. For example this one: MSP430FR6989 has current – at 1 MHz with 0% cache hit ratio – 0.375 mA. For Low Power Mode 0 (LPM0): 0.120 mA, for LPM1: 0.065 mA. Remaining LPMs are having current 0.001-0.009 mA. If software will query HC-SR04 twice a second – i.e. will sleep in a LPM for 500 ms after each complete action set – then I think I will obtain the desired effect of months on batteries.