Diode is a nice way to drop the voltage without a regulator. Looking on AliExpress the NL-5Cs are currently 81p. I'd either need to buy some sort of holder/mount which I bet is more expensive than the battery itself, or go for a screw and couple of pins to secure the battery.

I was thinking the same, to have it sat behind the board.

I've got a load of 18650s in a drawer too.

If I didn't have so many 18660s I'd consider getting some of them. Actually I probably have an old mobile I can rip a battery out of to see how well it would work.

Easy method to fix one in place here http://strofoland.com/arduino-projects/nokias-bl-4c-battery-holder-in-just-5-minutes/

ESP8266 modules have arrived. I can already think of a load of things other than temperature sensors that I want to make. Definitely going to end up ordering some more.

Are they little WiFi modules? Easy to use? What else you planning with them?

Once I figured out how to program it, wiring etc, it is now fairly easy.

I'll build a programming board at some point so I can just plug in the USB serial adapter and an esp8266 module.



Once it's programmed you can just power it up without all the buttons and adapters.

Made a quick test setup to see how well my new sketch works.



Pretty simple setup which I might solder to a protoboard

esp8266
ams1117-3.3 regulator module
ds18b20 temp sensor module

Rather than running a webserver on the esp8266 and another system requesting the data, the esp8266 now uses a http get command to send the data itself. This will mean once I tidy up the code I can have it deep sleeping when it's not needed, rather than being awake and ready to send.

Made a programming board



And made a temperature sensor board to play with

 

Turns out the ESP8266 can run off 4.2V so you can connect a lithium battery direct without a regulator to waste energy. 3x rechargeable AAs work well direct. Next step is to sort the deep sleep code.

I've bought some lithium charging boards to use to protect against over discharge. Another few weeks to wait!

Interesting. I didn't realise they could be run on their own. I assumed they needed an Arduino to connect up to. I wonder how well they run in sleep mode compared to an Atmega with RF24 radio connected.

The ESP-01 model (which I have) has 2 GPIO pins that are useful for stuff. The other models (eg ESP-12F) which have more pins available are a bit larger and look to be more fiddly to use, but I still might buy a couple since they're less than £1.50 each, you can get a mounting board for about 10p anyway.

ESP-01


ESP-12F


To use deep sleep you need access to GPIO 16, which isn't normally available on the ESP-01 (only GPIO 0 and 2). You need to do this...
(and my soldering iron tip is too fat :C )

I just got an esp-12f, not sure what I'm going to do with it, but for £1.57 including the adapter board it was hard to resist.
Soldering it onto the board was a bit of a pain though, and its too wide to use on a single breadboard.

Nice, you'll definitely be able to deep sleep with that then.

In deep sleep I think it's in the microamp range for power consumption.

I've read various reports of it now always waking from deep sleep which doesn't sound promising.

Yeah, I think I saw something about that as well. Doesn't really bother me at the moment, need to think of something to use it for first!

I actually thought you were the other Chris earlier :$

Sensors, switches, stuff to remotely control

Haha!
My next project is actually an 8x8x8 LED cube, just ordered the esp on a whim alongside the bits for that. Still waiting for my LEDs to turn up though.

Haha. I read your post and thought that was to me and got very confused :)

I'll stick to my RF24 radios for now, at least for my temp sensors because I've got them working nicely. I'll definitely consider them for other things though.

What you got planned for them?

My RF24 temp sensors are working well, but for some reason I don't like them. Range is ok but not as good as I expected, the kitchen one occasionally drops out (and that's got a proper antenna rather than an onboard one), even the bedroom one isn't always 100% and that's in the room above the RPi. It's easier to extend a WiFi network than an RF24 network - I've already got an AP at either sides of the house.

That's a good point about the range. I didn't think about that. I don't have any problems where mine are at the mo but last year when I put one outside for a bit it was tricky getting it to connect to my Pi.

If I ignore the deep sleep and running them off batteries, I now have a nice working setup for a plugged in sensor. I think I'll tweak/redesign the PCB now I know what components are sensible and needed and order some.

I'll probably change a few bits to enable multiple power options, maybe add a few jumper points for various options like disconnecting the regulator.

I'm also wondering how easy it would be to add some dip switches to give each module its own unique id rather than programming each one specifically.

It was only the other week that I got my AliExpress "Awaiting Delivery" list down to 0, it is now 20 (fail)

I need to stop buying cheap electronics.