Bluetooth Thermometer Minds Your Meats

The summer may have come to a close here in the USA, but any time of the year is a good time for grilling. In the colder weather, it’s a drag to have to stay near the hot grill to keep an eye on your burgers and franks. [Eric Ely] thought it would be smarter to have a meat thermometer that sent his phone the current reading via Bluetooth.

Instead of starting from scratch, [Eric] took an off the shelf electronic thermometer and removed its temperature probe (which was a thermistor). The hardware used an off the shelf Bluetooth board with a companion battery board and prototype board. If you can’t bear to cut up a good thermometer, you can get replacement probes that ought to work just as well.

In addition to the boards and the scavenged thermistor, [Eric] used a couple of resistors. One resistor is in parallel with the thermistor to improve the linearity of the device’s response curve. The second resistor forms a voltage divider that the Bluetooth board reads.

The software (using Node.js and C) is available on Github. The C program reads the temperature and pushes it out using JSON. Node.js provides a server that [Eric] can hit with his phone’s Web browser.

Sure, you can buy wireless thermometers, but what self-respecting hacker wants to carry around a store-bought box just to display meat temperature? Viewing it on your phone has much more street cred.  Of course, a real hacker isn’t going to cook on a conventional grill, either.

14 thoughts on “Bluetooth Thermometer Minds Your Meats

  1. Looks like a sales pitch for a product you can’t buy yet.

    If you want to achieve the same thing with hardware you can actually buy.

    Goto eBay and buy a HM10 BLE module. (current price is $2.80 inc shipping)

    Then you’ll need to flash it with BlueBasic https://github.com/aanon4/BlueBasic
    For this I’m afraid you’ll need to buy a “CC Debugger”, but again, on eBay you can pick these up for around $10 to $15

    Flash BlueBasic onto the HM10, and you can program it in Basic to read the ADC and send the resultant data over BLE

    BTW. I’m not sure why the article talks about JSON etc, surely as BLE device, its not sending directly to the a web service using AJAX and JSON ? Its just broadcasting BLE packets that the phone can read, isnt it ?

    If you wanted to do the same thing and put the data onto the web, an ESP8266 is a better option (apart from the power it takes), as the ESP8266-12 module has an ADC input (0 to 1V input range), and its easy to code using the Arduino IDE to connect to your wifi AP and then post to the web.

    I’m sure you could then get Push Notifications sent by your web server back to you phone, if you had the time to code it all up and register with Apple etc

    1. Bluz aims to be a bit more involved than just broadcasting data to your phone, it will use the particle cloud system (known from Particle core and photon), via a gateway which can be a USB stick, a phone or a particle photon board.

      So the json data that the unit transmits will eventually end up in the cloud without you having to explicitly code it, and you will be able to load new software to the unit etc.

      Its a bit more expensive than the raw BLE module, but you get a lot more functionality, well hopefully, I only know what can be learned from the forums etc. since the product is not out yet…

      1. I still don’t see what the BLE hardware has, that a lot of other BLE devices don’t have

        e.g. BBC Micro:bit.

        Most programmable devices could have code written to send BLE via a gateway to a cloud.

  2. I found out the hard way about leaving a temperature probe in meat on the grill….
    While the internal temperature of the meat was less than 100 C, the temperature of the air around the meat
    was more than twice that, and the insulation of the probes cable melted and shorted the probe.

  3. Needs more beef. Please tell us the thermistor specs, resistors used etc.
    The s/w does not linearize the thermistor beyond y=mx+b equation. The Steinhart eqn is not hard to implement if you know Beta instead of empirical measurements.
    I like 0.05C accuracy so I lower self-heating errors by toggling an I/O pin instead of always leaving the thermistor powered up.

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