How to (correctly) use the pro mini with batteries

[LastSamurai]

I am currently working on some battery-powered sensors here. After some short time the sensors are always failing. I think due to brown out detecting, because its always at around 2.7/8V.

So I was thinking about how to use the pro mini (3.3V version) with batteries. I found some similar topics, but none could really answer my questions.

• I guess running the pro Mini at 1 MHz would improve battery life?! Is this supported by mysensors (or does this simply work with arduino code anyways?)?

• What are the "right" (tested) fuse settings for low power (no brown out?, 1Mhz?,...?) settings?

• Do I need a step up converter to fully use the batteries? The mini and the nrf should work with lower voltages too afaik, but I don't really know about sensors like the DHT22. Has anyone tested something like this?

Thanks for your help guys!

[scalz]

Hi. some ideas if you want:

• 1mhz can improve things. just for info, in case you use serial comm, frequency and baudrates are related. but for sleep mode, it should work. 1mhz frequency can be set with arduino code. I am not sure if there is a mysensors routine, I don't think so.
• I don't remember all exactly but what I do is : 8mhz (or you can do 8mhz internal rc) , wake up mode -> brownout=1.8v, sleep mode -> no brownout.
• you are right. if you want to fully use the batteries, a step up is needed. and bonus, you will have a constant 3v for radio (better range I think) during all the battery life. for example, mcp1640 (I use it) is 0.65v input mini. but of course at 0.65v you won't have full power current (I don't remember exactly, it is in datasheet)

[LastSamurai]

Thansk scalz! I guess I will stick with 8MHz then for the time being.

I looked up the arduino IDE's standard settings for the Pro Mini and only changed the BOD Level to 1.8V. The following fuses were the result: Low: 0xFF, High: 0xDA, Extended: 0xFE
Somehow I can't flash new fuses atm but I will try these settings soon. If I also remove the LED and perhaps the onboard power regulator I hope to get better results.

Ok I guess my next version will have a step up converter then. How much do they themselft drain the battery? Is it worth the cost?

[LastSamurai]

Does anyone know a good step up regulator thats available on ebay (or somewhere else I can get it from germany), not too expensive, works with my own pcb and draws little power itself?

[mfalkvidd]

Some good regulators are available in these threads:
http://forum.mysensors.org/topic/1902/good-step-up-down-regulator-for-battery-powered-sensors-3-3v
http://forum.mysensors.org/topic/486/my-2aa-battery-sensor
http://forum.mysensors.org/topic/483/2-aa-batteries-with-step-up-converter-to-vcc-pin-vs-3-aa-batteries-to-raw-pin
They all have their benefits and drawbacks. Selecting one that suits your needs should be possible.

[tbowmo]

If you are going to let the node go into sleep between sensor readings (f.ex. Wakeup every 5 minutes or so) you don't need the troubles of switching to 1Mhz.

When you sleep the atmega, you also turn off the oscillator for the MCU. So it doesn't use any power.

In fact one could argue that it will result in a longer wake time if you are running at 1Mhz instead of 8Mhz, due to the slower execution speed. And so it could end up using the same amount of power, as when running on 8mhz.

This is however untested/unverified, and just a theory that I have..