Monday, October 5, 2015

The final CC2500 Device

All this work on watches, and discussions about how small this device could be, got me motivated this weekend to make another (last) device.  This took the whole weekend.  Fiddling with eagle, realized I could do it without jumpers, and I left out the serial interface for programming.  Leaving out those traces makes a huge difference, no issues with trying to sneak by the CC2500 antenna.  Program the chip before installing...

Screenshot from eagle:

From the left:  Rfduino, CC2500, and a Polulu 5v to 3.3v converter.  Used a 40 maH lipo which fits on the top right.  I realized after the fact that I could make life easier on myself, and have dedicated pads for the lipo, that aren't so close too each other.  As it is, the lipo is directly soldered to the pin-header socket.

Completed device, in 3d printed ABS case.

It's almost bic lighter size.

A shot of the board, Dexcom for scale :)

And in it's charger base.


  1. Wow! Looks like you've been busy. Is the RFDuino still acting as a peripheral device? You might get better range on the RFDuino if you turn it 90 degrees counter-clockwise to keep the antenna away from the copper traces. Would that make routing the traces easier?

  2. Wasted a weekend, but I can't even tell this device is in my pocket. RFDuino has to be a peripheral (unless I reflash with Nordic via segger). I'll use BLE Nano for Central. Never had range issues with the RFDuino, that ceramic antenna is great, the traces are above it. Agree it could be rotated. Didn't re-think that after removing the tx,rx and reset traces. Thinking today about putting a surface mount piezo / pager vibe on the "free" space left on the board.

  3. It's not a wasted weekend. It's good progress. Does the pebble do central? or are you using the BLE nano in the wristband?

    I was looking at the Nordic chips that RFDuino is based on and it looks like it can do BLE + proprietary protocol. I wonder if it's possible to put TI's SimpliciTI 2.4 Ghz protocol on the nordic chip and alternate between BLE and dexcon G4. I don;t have a segger j-link or SDK for Nordic.

  4. Pebble is a peripheral. I want to put the Nano in the wristband as a central device, which can pair with the RFDuino, without any code changes. Not a chance on doing TI's RF protocol on an RFDuino. There's a hardware layer. Same reason no one is doing bluetooth with a ble chip or vice versa. SimpliciTI is a software abstraction over SPI, you don't need SimpliciTI.

  5. I thought SimpliciTI was the 2.4Ghz protocol being used in their chips. I'll read up on it some more. Thanks.

  6. Why can't the Nano be in the rig instead of having the RFDuino?

  7. You could use the Nano. You'll need to change the code a bit, and figure out how to get it to sleep properly. It's a bit bigger than the RFDuino, but you'll gain back space since you won't need the voltage regulator.

  8. Hi, What are the dimensions of the box you're holding in the picture above?

  9. Are you going to be working with just the RFduino for the G5 that has no come out? Seems like it could greatly reduce the size and complexity. Maybe just a dual sided PCB for the RFdruino and the power supply?

  10. That's a long way off, I don't like the reviews, I'll go to the G5 when I have to.
    For the G5, I'd recommend the BLE Nano, or plan on reflashing the RFDuino. If it's possible to do the pairing the Nano handles Central mode. In either case dual sided wouldn't buy me any space (that I can see), so don't bother.

  11. The biggest issue I saw with the g5 was consistent connection to the iPhone. Are you aware of any other problems? Haven't gotten one yet but should be later this year, in which case anything other than smartphone integration would seem like redundant hardware. Although could end up being more reliable. I just checked out the nano and was wondering if you went with it, would you be using their arduino library? I guess it's not as functional as the other's but might provide enough to send and receive packets from the dex

    1. Downsides to the G5, no access to raw (assumed). I'd be back on the 7
      day sensor cycle. Also, don't know if I can get the data myself. The
      iPhone connection issues and being forced to an apple watch. It's
      interesting they have issues with the connection, I see those myself
      with my devices, but sometimes they stay up for days, but, it's easy
      to block the signal to the various devices because bluetooth just
      isn't that powerful. The important thing is the device has to notify
      you when it's no longer able to connect, it sounds like they don't do
      that, and that's ridiculous.

      I can use the Nano as a central to an RFDuino, seems fine for that.
      Question remains, what else will be required to pair with a sensor.
      It's very easy for the designers to make this very hard. I still need
      to spend some time with my ubertooth and see if I can trace btle
      packets for the various devices I'd like to have control of (Dex,
      Vivosmart, pebble).

      I'd use the arduino library if I could. With the nano, if you can't
      use Arduino, you'd have to go back to iAR(TI) , and that's not
      happening(ie. I spend enough money already, I'm not buying an iAR
      license for a hobby).

  12. I've heard that Dexcom will only let the G5 connect to one smartphone and their receiver. Nothing else after that. Some that have it already say that it's difficult to re-pair it again after that. Because Bluetooth needs both sides to be transmitters and receivers (transceivers), I'm afraid that Dexcom may restrict access to the G5 to only Dexcom devices and apps using some kind of encryption key.

  13. Going back to your mention of using the ble nano, what do you think of its ability to work with the nrf905 sub 1ghz module to use a phone to control an omnipod? Have no experience programming but think a project like this would be fun to learn on. Just need something easy to understand like arduino and compatible hardware. From what I've read there is no security implemented in the omnipod so it would be a matter of being able to mimic the little PDA device using and Android phone and the modules I mentioned as a bridge. What do you think?

    1. I think Lorelei was messing with that, and gave up. That's an
      interesting module, nano definitely has the pins for it, I think the
      RFDuino has just enough. Messing with RF is anything but easy
      This is the one pump I would almost consider wearing, and if I could
      control it :).