I bought an ATMega328p chip a while back to try and make a barebones board but couldn't get it working. Also, the price of the parts was far more than buying a Nano or Pro Mini so it seemed a little pointless.

I have seen some people running strip down boards off button cells for a very long time, usually only transmitting something occasionally though.

I might try a 433 MHz transmitter on a temp sensor setup to see how well that works.

http://jeelabs.org/tag/lowpower/

I think it /should/ be easy to get working at 8MHz. Shouldn't need many components, maybe just a cap. Maybe not so easy to sort out the boot loader. It worked out slightly cheaper to buy the chip than a Pro Mini, about 20p I think. Amazing they can sell a fully assembled board for only slightly more. Maybe the DIPs are more expensive.

I have another Pro Mini just sending it's battery voltage. That should last months. So something up with the other one. Either somethring to do with the temp sensor or the Mini.

Is there a less power hungry way to read the temperature? What about a pressure sensor in a sealed tube and use P1/T1 = P2/T2 to sovle from a reference temp?

I imagine it's the wireless transmitting of the data which uses more power out of everything.

(I think) The problem is the sensor itself. It needs at least 3V so I'm using a step up to increase the battery voltage. I'm switching the power off to it when the Arduino goes sleep. When it powers on again I get a temp of 85C unless I delay the reading by about half a second, so it's staying awake too long each cycle. The actual sensor uses very little.

I wonder if leaving it on would be better. Will leaving the step up on waste much? My other option is to switch the sensor on, go to sleep for 0.5-1 second, wake up, read temp.

I think I'll remove the temp sensor, just send the voltage, and see if it is the temp sensing that is draining the battery.

Or I could just lick my finger and point it in the air. Or is that for wind direction?

Stupid me. Change delay to powerdown .

Didn't even help a little bit. Exactly the same drop in volatte. Need to do some investigating.

Graphs!

I switched off the temp sensor this morning. It is now just sending 20C every 80 seconds. Doing exactly the same as my battery test module and the battery use for both is completely different.

The green line is the one with the sensor, the red is (roughly) the other module.

Not sure what's going on there.

Do you know what? I think it's the Arduino that's the problem, not the circuit/code. Maybe the way I removed the voltage regulator or cut the LED trace. Must be some leaking current somewhere.

I have another module running off a different 3.3V step up. Not switching power off to anything. And so far the voltage is steady. I removed the LED but the reg is still there.

Not had it running long enough to work out how long it's likely to last yet.

Well no wonder I'm not getting the battery life I want. This thing is using 2.2mA when sleeping with nothing else plugged in or working. Not too good. I've got my multimeter current sensing working. The fuse had blown. Made a little shunt to bypass it for now.

Nothing like the potentially 1uA some people have got them down to. More work to be done.

I've had some success with the barebones Atmel chip. I plugged it into the breadboard and tried to connect with AVRDude and nothing happened. Silly me, I didn't connect the crystal. It has an Uno bootloader so was expecting 16MHz.

I've set the fuse bits so it can run off it's internal clock, pulled the crystal out and AVRDude connecting now. Just need to work out how to program it now or which boot loader to give it.

/Much/ better. 28uA when using the same sleep test. Wonder if I can get it down further.

Ive done a little bit of testing tonight. Running off the batteries I got a powrr consumption of 22uA. When I connected the battery to the 3.3av step up and used that to power the Atmel it increased to 81uA. 4 times as much.

I was playing around with my barebones last night (YJ), programming it with my USBasp. It was programming fine but as soon as it reset to actually run the sketch nothing happened. It would occasionally work when I switched the jumper on the USBasp to 5V instead of 3.3V.

Strangley plugging it into the battery worked fine. I think I shorted something on the programmer (I plugged the + and - into the - on the breadboard) and broke something on it.

Had another 1 (supposed to be 2, only 1 turned up) Atmel chip turn up but couldn't get that one to work at all.

This has been driving me nuts. I've been modifying the examples for the temperature sensor and radio to test switching them on and off and I could get them working. When I added it to my temp logger code things didn't work. AARRGGHHH!!

I /think/ I may have finally cracked it though. Not sure it is working 100% reliably though, I will have to test that. But I have something on a breadboard that consumes about 4uA when sleeping. Should last a while on batteries.

The radio works fine. It was the temperature sensor that was the pain! The 3.3V step up uses about 90uA not doing anything so I didn't want that going all the time.

I had forgotten I'd ordered this. I think I must have done it when I'd had too much wine. Turned up this morning. 10x Atmega328ps and crystals, caps, etc.

How much does that work out per complete unit?

£1.99 each from the UK.

I've also control  Light in the bedroom
(http://www.ledlightmake.com/led-lamp-c-77_78/e27-led-bulb5w-multicolored-rgb-16-colorwith-remote-control-p-203.html)with MCU(PIC12F675).