I have a very successful run managing to program and use the ESP-01 module standalone.

(I actually completed all this by yesterday, then today this article about natively programming the ESP-8266 came out on the main hackaday feed! As it turns out I took a slightly different approach, which I think long term will work better for me anyway)

I started with the frankenstein firmware by necromnt, which uses the Antares kconfig-based build system to build a uboot-like environment for the esp8266. I was quite easily able to add a DHT11 module, the results are now in the latest git for that project. I was actually quite impressed at how quickly I could get everything going, compared to other frameworks I have used.

The next step I did then was to strip down frankenstein to a bare hello world program, essentially ending up with just a user_init() function with a few extra bits, but now with a nice build system that just seems to work: the deployment cycle is now simplified to two commands:

make
make esp8266-deploy

The only thing that didn't work was deep sleep mode (documented here by Matt Callow). Turns out to make it work on an ESP-01 you need to hack of an LED and do some other hardware mods. Not that I'm averse to doing that, but I want to design the sensor to be easily constructed...

Functional deep sleep mode will be required to ensure I can run the sensor on a small solar cell and AA rechargable. In the meantime, I'll code up a version that just uses a timer. It will be interesting to try and empirically determine the power usage differences.

So now on my shopping list is an ESP-12, a breakout with all I/O pins exposed...