Thursday, April 30, 2015

Building a CC2500 to BLE Adaptor

Posting some details in response to questions about the current module.  Everything for the CC2500 is on Github,  Fish around here and you'll also find some iOS and Pebble code.  Sorry, nothing Android based.  

The RFDuino is programmed like any other Arduino, it's worthwhile to use their usb shield.  The CC2500 is controlled via SPI(from the RFDuino), there's nothing to program.


The schematic is missing the 3 volt regulator (Pololu), and the battery for that matter.  I just added pads for it into the PCB, I don't spend much time in Eagle, so it's a painful experience.  One jumper in this version, from the CC2500 VCC to +3, you'll see the pads in the middle.  Also, I've added a 100 micro farad electrolytic capacitor across the +/- leads.  The device tends to crash when you plug it into the charger, the Cap reduces this (maybe).  Not really a big deal, since all this does is relay what the CC2500 receives to the iPhone.  

Everything is surface mounted, whether it should be or not.  Keeps the board thin, and drilling is a pain.  The device is always on, makes for some fear when soldering the lipo, YMMV.

Still considering going thinner by using a smaller battery and recessing it into the board.  But, we're talking about a 0.1" improvement.  Battery life with a 110 mAh lipo is about 48 hours.


  1. Hello Don, Thank you for this project. The value that is display on the iPhone is Raw value or you make some computation in application? Thank you

  2. Hello Don, I want to ask you if all the computation is made only in iPhone apps; from the CC2500, through RFDuino bluetooth module, you transmit only the RAW data or you make some calculation inside the RFDuino? Thank you for support, Mihai

  3. Hi, Thanks for the blog. It's great! My niece just got a G4 and I think I'll try something like this since I've had a couple Wixels sitting around for a couple years. Have you considered making a watch with the wixel, a battery, and an e-ink display? Maybe the VTech Kidizoom smartwatch would work for the housing.

  4. I'd use a CC2500, not the Wixel. It's big, and I don't think anyone has got it to sleep reliably, so it's a battery hog. Also, you're almost out of memory on the wixel just loading the code to get the dexcom packets...

    I've been wondering if I could carve up my Nike Fuel and do something like this. Even got some ninja flex for the printer. Unfortunately, a hobbyist can't approach the level of miniaturization that's in these gadgets.

    You could almost do this with the Pebble time, but between a microcontroller and a cc2500, you're going to be 2ma(ish) over what they recommend.

  5. Just power the micro + cc2500 combo separately from the watch. So, I say look into the Pebble Time and Smartstrap, you could set yourself up with something that would work without the phone for periods of time.

  6. Ok, I'll keep looking around for something smaller. I'll start playing with the wixel code to see if I can bring it down some. I have some time before we get the Dexcom and G4.