Wireless brewing temperature sensor

I'm planning to build a wireless temperature sensor to assist someone in their hobby, brewing beer. Periodic temperature report is all that's required, no control at this stage.

I bought the NRF24L01+ kit, so the next steps are:

• Finding a temperature sensor suitable for immersing in liquid (with a sterilised cover)
  
• Working out how to power the Espruino for (at least) a few days. I have a few old phone handsets so I'm hoping to use the batteries. There is no mains power where the beer is fermented.
  
• Working out whether I need to use the other Espruino to receive SPI and communicate over serial to a linux machine. Ideally, I won't need to do this and can use SPI directly from the linux machine.
  
  

As you can see, the plan is very rough so far. And I haven't used SPI before so I'm not sure of the range or what I'll need on the linux side.

Hmm. Sounds good - next step is trying to control the temperature, any maybe counting bubbles :)

• DS18B20 sensors say they're waterproof. If you used a grommit (or glue) and pushed only the stainless steel bit into the beer you could be pretty sure it was sterile too.
  
• Espruino should manage that easily on an old phone battery. Even on a 700mAh from an old Nokia (Galaxy S3 is ~2000mAh) battery it'll run in sleep mode for 6 months. Just use setDeepSleep(1) and only wake the radio up when you need it.
  
• It depends - you might be able to find a USB NRF dongle. I'm not sure which Linux computers have SPI - but a Raspberry Pi or some OpenWRT device would have it. If you had a bit of time, it'd be awesome if you could implement the SPI on Linux for Espruino (shouldn't be hard - it's just file IO), and then you could run Espruino on your PC and use the same NRF24 drivers :)
  
  

Hope that helps - happy brewing :)

Heh, excellent bubble counter. Thanks for the suggestions.

Happy to contribute any code that others might find useful - will take a look at what's required.

Li-Ion bateries (I mean for example those used in cellphones) are affected by self-discharging process (up to 2% per month). Of course it is much better than in older NiMH batteries but anyway we may get much more electricity than we expect after a few months.

Also battery age is important when we consider reusing of old phone batterry - the potential capacity might be also affected seriously.
Bogdan

Of course instead of "may get much more" I meant "may get much less"
Bogdan

@motter, nice project. Remember to make the sensor "food grade" when putting it in stuff you are going to ingest :) Adafruit carries both a waterproof ds18b20 and food grade tubing. You'd want something like that.

Is the brewery within wifi range?
Using a CC3000, and having it post the data by periodically connecting and firing off an HTTP request containing the data might make the computer side of it easier. Wouldn't do any favors for the battery life (WiFi draws a fair amount of current, though you can and should keep it turned off most of the time).
I'd rather write a PHP/etc script to extract the data from the request than figure out how to get an obscure piece of network hardware meant for comparatively primitive systems working on any desktop computer, let alone linux....

Since it's a stationary installation, you don't even need lipo batteries... 3 or 4 NiMH AA's would be fine (careful with input voltage to CC30oo), and would have the advantage of being cheap to replace, chargeable with normal battery chargers, and alkalines could be used in a pinch (the beer must flow!).Whether this would be cheaper, I don't know. Remember, since there's no mains, you'll need at least two sets of batteries to keep this running. And maybe a juicy cap across the batteries so it doesn't reset when you swap the batteries...

Or you might be able to use a solar powered USB battery pack. They're pretty cheap now. I'm not sure quite how much power the panels produce but I'd imagine it should be enough to keep WiFi up for 30 seconds a day.

I'm quite interested in SPI for other reasons and already have the module, but it's worth bearing 802.11 in mind if it proves difficult.

In theory it shouldn't matter if it's reset when the batteries are changed (as long as it can reconnect) since whatever persists the readings will use its own clock.

@motter For your temperature sensor, checkout https://www.atlas-scientific.com/product_pages/sensors/env-tmp.html and for an example on how to get the temp probe to work with the espruino, http://forum.espruino.com/conversations/680/newest/ .