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Calling All Thermocouples

OK, so I’ll admit it… I love the nostalgia of analog devices.  As a kid I assembled a rolling ball clock – the kind that resembles an intricate, miniature roller coaster, where time is measured by the number of balls on each “track”. I loved it! Unfortunately, it woke the whole house up at midnight, so I, alone, was unanimous in that, but to me it was the most wonderful invention I had ever seen.

The programming side of my brain, though, makes me a fair-weather friend to analog devices. For all their nostalgia, sometimes digital is just plain easier… and better. Such is the case for me with my roasting thermometer. There’s absolutely nothing charming about craning my neck upside down to read the accurate bean temp at regular intervals throughout a roast. And, though Roastmaster makes it easy to input temps with the keyboard, an automated solution would be much better.

For some time now, I’ve been wanting to make the jump to something digital. I’ve held off, hoping I could find a device that I could integrate with Roastmaster to accommodate the automated readings. There are endless USB data loggers out there, but without a USB port on any iOS device, they may as well be turkey probes. I did find a high-end Bluetooth thermocouple as well, but any price that is listed as “Call for quote” is usually just too ridiculous to display. I did, by the way… and it was.

I was hopeful when the iGrill bluetooth thermometer was introduced. It’s basic, but it’s an all-in-one package that looks great, and would do the trick, as long as the makers would release the SDK for other apps. Or, so I thought – turns out it’s not capable of reading temps high enough for coffee roasting. I’d like to talk to the manufacturer and see if this is hardcoded in the electronics, or simply a limitation of the probe supplied with the unit. For the moment, though, mine is sitting quietly and sadly, unused.

I’m aware that there are build-it-yourself open source Arduino solutions out there. I’ve researched one, and it is feasible from what I can read. I had hoped for a prepackaged solution, since we’re coffee roasters, not electronic engineers. But, being in this community for quite some time has taught me that often they do overlap. I’m thinking I may just take the plunge. Being open source – I anticipate it will work well, but probably won’t win any beauty contests. Still, though, it will give me a tool to at least construct the framework Roastmaster will need to work with these devices, and as new solutions come to market, those will be as easy to add as creating a device description for them, or so I’m hoping.

In the mean time, if anyone knows of a Bluetooth, LAN or, dare I ask for it – an iPhone dock-style thermocouple – available for a reasonable price, with a public SDK, please let me know.

Cheers and Happy Roasting,

About the Author

Danny HallHome Coffee Roaster and App DeveloperView all posts by Danny Hall »

  1. Jerry Kalpin
    Jerry KalpinMay 13, 2011

    I don’t think you’re going to find a thimble-size temperature xmitter (bluetooth) that could sustain (say) 700F and has a signal strong enough to penetrate a metal enclosure.

    Then …you are left with a thermocouple lead somehow exiting the enclosure to feed a bluetooth-capable thermocouple reader from which a signal is sent to your iPhone or iPad.

    My TENMA 72-7712 thermocouple reader will capture 100 data-points internally or will output them (endlessly) to your PC via a USB port. While the software was designed for Windows 95 (I think) it does work and it arrives in my PC as a *.xls file.

    What you might look for is a USB to Bluutooth transmitter to take the data stream from the thermocouple reader to your iPhone.

    • Danny Hall
      Danny HallMay 14, 2011

      Hi Jerry

      Correct – it would have to be a k style thermocouple sitting outside the roaster. That’s how the open-source Bluetooth Arduino would work.

      I’m thinking the same thing about adapters/transceiver. Best case scenario would be a USB->BT converter that people like you with existing USB thermocouples could attach and broadcast via Bluetooth instead of USB. That would rely on the manufacturer making the API for any given device available, as well having a public API for the converter, but it seems doable.

      I’ve found, though, that even there are a ton of USB->Bluetooth dongles, they are all designed to sit on a PC as a hub. Nothing exists (that I can find) as a stand-alone-converter that attaches to a device to work the other way around. I understand why – USB is much faster than Bluetooth. Plus, it would have to have a power source, so it would only make sense for specialty applications like this, so there wouldn’t really be a big market for a manufacturer to appeal to.

      Of course, this point would be moot if only there were a USB port on iDevices. 🙂


  2. Jordan
    JordanMay 23, 2011

    Perhaps the dock connector > USB adapter ( would work for existing USB data loggers.
    I’d much prefer a wireless solution (arduino would be fine by me), but this might be a simpler alternative in the meantime. I can’t wait for thermocouple support!

    • Danny Hall
      Danny HallMay 25, 2011

      Hi Jordan

      Thanks for the link. I knew the adapter existed, but had dismissed it based on what I already know from the dev side of Apple and the infamous dock port. I had another look, though, and was able to dig up some info from an Apple engineer on the forums about the adapter.

      Any workable solutions that I can fathom would still involve having the datalogger restructure the data it generates in some way or another – so, we’re armed with a bit more knowledge, but still in the world of Arduino. Seems they’ve discontinued their all-in-one Bluetooth board in favor of a modular BT solution – the Bluetooth shield. At first glance looks like the price would fall to under $100, so this is definitely a good thing.

      I’m going to go ahead and get my hands on the Arduino hardware. I had the parts picked out, but am going to change and build around the new BT shield.

      Thanks for the link and feedback!


  3. Jerry Kalpin
    Jerry KalpinMay 28, 2011

    If you are looking for a low-cost ‘configurable’ platform, have you considered ‘iWavit’?

    Look here …?!


  4. Danny Hall
    Danny HallMay 31, 2011

    Hi Jerry

    I’ve never seen this – what a cool product! I thought my old-school Logitech Harmony remote was slick – this makes me realize I’m really behind the times.

    It took me a while to figure out exactly what this thing does besides control TVs and desktop computers. I was thrown by the “Over 25 Apps” slug on the home screen. Looks like those are just variants of different vendors’ remote controls. I think that this is just geared toward controlling infra-red devices – TVs, DVDs, cable boxes, etc. Unless there’s something I’m missing, the device itself is a proprietary device – the USB dongle is just for plugging in to a desktop and letting the iphone control it as an “air-mouse” – like the Wii controllers do. There would be no way to use it to receive data. Even if it were an open-source device, it wouldn’t be able to accept incoming data.

    Thanks anyway

  5. Jeff Kilpatrick
    Jeff KilpatrickJun 01, 2011

    I’ve been quite pleased with the Phidgets temperature sensor. It’s $60, is usable on many platforms (including OS X) and could be accessed using their API over a network, saving the cost of a custom iOS thermocouple. It took me about 20 minutes to put together a basic roast tracking app using their API; it’s really sweet.

  6. Danny Hall
    Danny HallJun 02, 2011

    Hi Jeff

    A user emailed me about Phidgets a few weeks ago. At that point I hadn’t heard of them. They’re much more specialized than Arduino, and I’m sure a lot easier to work with. Honestly, I’d rather go that route than Arduino, for that and cost reasons, but they all rely on USB. The one you recommend would technically work, but it would need a PC or laptop to tether it to, running their Phidget WebService to rebroadcast the data before an iOS device could access it. I actually had an order submitted last night before I re-read the fine print and realized the card didn’t have wireless capability. The description in the API made me think it did, but it needs a host computer to interface to before the WebService can work. So, I cancelled it, and order some Arduino gear. The Uno, XBee shield with wireless, two Max 6675 chips and a couple of thermocouples.

    Thanks for the pointer anyway – I appreciate it. I want to keep my eye on them, now that I know how iOS friendly their APIs are. It would seem only a matter of time before they come out with a wireless board, if not Bluetooth.

    You app sounds intriguing – what platform?


    • Simon Chang
      Simon ChangJun 04, 2011

      I think you don’t need the Arduino platform. It would be more easiler to design a simple system with Lan|Wi-Fi or Bluetooth interface.
      iPod would “talk” with the system via any one of these interfaces without any customized API.

      • Danny Hall
        Danny HallJun 05, 2011

        Hi Simon

        Thanks for chiming in. Can you elaborate? That’s my goal, but Arduino is the only thing I’ve found that is A: Open-source, B: provides a Bluetooth or LAN interface, and C: will accept thermocouple input that can be routed with code out of the PC board and into the iOS device.

        If you know of other hardware solutions that don’t rely on USB, please let me know.

        The problem is, I’d rather not have to build anything at all. Many users already have their own USB thermocouple/data loggers, or could purchase them very cheaply. If there were a way to interface them to the iPhone, I’d try that route first. But, there’s no way to plug them into an iOS device. Even with the USB camera adapter that Apple sells, the data generated would need to be reformatted by the device to work.

        Now, it would be possible to write an intermediate driver for a host computer that a USB device could plug into, that would then rebroadcast that data to an iOS device – IF the device provided SDKs to access its data, or was in a decipherable format, but that would require putting a desktop computer or laptop, roaster AND the iOS device all next to each other – that just isn’t feasible to me.

        The Arduino I have on order is actually LAN-style, though I can get a Bluetooth plug-in module for that board. LAN is cheaper, so I’m going to start with that – for the users that might want to try it for themselves. For the mean time, I’m 99% sure it will work, and will allow be to start developing the GUI interfaces Roastmaster will need to work with external thermocouples.

        I’m curious to know, though, exactly what you mean. If you think there’s better hardware please let me know.


  7. Simon Chang
    Simon ChangJun 06, 2011

    Would you advise me your major goal? Do you prefer to publish the hardware with open-source code or sell the cost-effective kits?

    It’s not difficult to design a tiny and delicated system(board) with native Lan|Wi-Fi and Bluetooth interface. It would send out the thermocouples data over the LAN packets. It can directly “talk” to any devices with LAN protocol. To get the thermocouples data over the LAN packets, you should have the TCP/UDP programming skill.

    • Danny Hall
      Danny HallJun 06, 2011

      Yes, you’re right, but I’m not a hardware manufacturer. If I were more of an electronic engineer, than a software engineer, I might be considering trying to bring something to market. There’s definitely an opening for this type of device. But, I’m focused right now on the software side of things, so I wouldn’t want to try anything like that at the moment.

      That’s not to say I won’t change my mind, it’s just not my area of expertise. The Arduino gear arrived today, so I’m going to get that up and running and see how that goes. That will let me get started on software development to support it. Once that’s done, I might reevaluate if nothing good has shown up on the market yet.

      Do you have manufacturing ties?

      • Simon Chang
        Simon ChangJun 08, 2011

        Please e-mail me. we can discuss the hardware in more detail.

  8. Peter Webb
    Peter WebbJun 06, 2011

    Here at ETI we have developed a thermocouple Bluetooth probe, this probe will be launched during the summer of 2011. The probe has a wide temperature range, and is very accurate. We are just working on the Apps. If you want more info then e-mail me.

    • Danny Hall
      Danny HallJun 06, 2011

      Hi Peter. I sent you an email. I’ll be on the lookout for your reply.


  9. Danny Hall
    Danny HallJun 16, 2011

    Well, turns out I’m not too bad with a soldering iron after all. The Arduino prototype is up and running, though only via USB to a console at the moment. I’m still waiting for the Bluetooth module to arrive.

    So far I’ve discovered that my body temperature is normal, and that thermocouples don’t taste very good.

  10. Rodrigo Ramos
    Rodrigo RamosJan 18, 2012

    I have a datalogger with 3 thermocouples that stores data in excel format. Can you plan to import data into roastmaster?



    • Danny Hall
      Danny HallJan 18, 2012

      Hi Rodrigo

      The next update has import/export of certain data types, but at the moment only a few types of Roastmaster data that users are wanting to share. But… I built that to be a starting point with things like you’re describing in mind. I was thinking mostly of adding export to excel-type formats, but could definitely see the benefits of being able to import data like you’re describing.

      Can you send me a sample file of what the data logger saves?


  11. beanman
    beanmanJan 23, 2012

    Hi Danny,

    Love your app, especially for the ipad! I think I have a wireless solution for you for just around $300 and all “off the shelf” parts. Did you ever check out So here is how I think it should work, even though I did not build a prototype.

    – thermocouple board: which works with J, K, E and T type thermocouples. Should work for almost all roasters.
    – Single Board Computer, SBC: which you can connect the thermocouple board to via USB. The SBC runs a full Debian Linux so you can do (almost) anything with it.
    – Wi-Fi adapter: to connect an iPad/iPhone to the SBC via WiFi. The adapter connects to the SBC via USB.
    – iOS support directly from I think that is the best feature of this setup. So it should be easy for you the integrate it into you app.

    As far as I understand all components, they should be easy to configure, no soldering needed, and should get you in the end a WiFi reachable thermocouple which streams the roaster temperatures directly to you iPad/iPhone app.


    • Danny Hall
      Danny HallJan 23, 2012

      Hi Beanman

      You’re absolutely right – the key is Ethernet. Apple HAS to leave that open, so I can’t imagine that apps that leverage ethernet would be in jeopardy of being rejected.

      I had looked briefly at Phidgets back when I was ordering parts for the ThermoTooth project, but (if I remember right) they didn’t have anything competitively priced for Bluetooth at the time, so I stuck with the original Arduino route. Now, of course, I realize that that is a no-go from Apple’s standpoint without the magic chip, so Ethernet remains the only viable option outside of becoming a manufacturer and making these things myself.

      I knew Phidgets had iOS support of some kind (another user pointed that out), but had never seen the actual documentation with examples – thanks for the link! When I built the “ThermoTooth 3000” I got the XBee shield that’s compatible with an ethernet controller. I’m going to revisit this now that v3.0 is done. That’s officially my only area of coding focus, and this is great info to have.

      ETI is preparing to announce their Bluetooth probe, but I still want to support homemade devices like this, because – at the moment, that will be the only option for the traditional K-style thermocouple until somebody makes a commercial version.

      Thanks for the links – I’ll read up some more on it. Also for the kind words!

      Kind regards,

    • Danny Hall
      Danny HallFeb 01, 2012


      Parts are on order – I can’t wait!! I opted for the 4 channel thermocouple board, though. I plan to support as many probes as needed per app, so will need the multiple channels for testing. Plus, given the automation – I’ll want to track bean mass as well as ambient temp myself.

      Thanks again for pointing me in this direction!!!!


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