Wednesday, January 2, 2013

The Bluetooth-ANT Bridge concept


I’ve talked about it a little, but I figured I should outline how the Bluetooth-ANT Bridge concept will work. I’d love to call it Blue-ANT but another company already has that, and BLANT sounds really stupid. ANTBL? ANTBuLL perhaps?

Anyway. The ANT+ Transceiver has 3 modes of operation, bit mode, byte mode, and Async mode. Bit and Byte modes are akin to SPI but the big difference is that the ANT+ transceiver (AP1 or AP2) is the master. For Arduino style projects this can pose a little difficulty as you’ll need it to interrupt the current code, handle the receiving, and then continue. I’ve had issues with interrupts in the past. However “Async” is pretty much the serial mode that we are all used to.  It’s buffered so long as you check your buffer for data every so often it’s not a problem.  But with this, that can all be handled by software. So it should just be a direct connection to the Bluetooth SPP (Serial Port Profile) board. I have to check the voltages.

I still have a discontinued ANT+ Sparkfun module I mentioned earlier. Basically it just needs to be wired as shown in the image above. I haven’t noticed RTS being 100% necessary but I’ve seen it mentioned on the “thisisant” forum as important and it might be one of the reasons I’ve had some issues communicating with the AP2. I seem to miss receiving updates that it’s sent a signal… this is causing miscounts for the crank torque profile as every 4th message should be basic power.

Some potential issues after the jump.

Simple right? Why doesn’t it already exist? I haven’t got a clue, but for 10 dollars I’ll find out and let everyone know.

Potential issues are:

1) Battery Power: Could be pretty high consumption. The Bluetooth module is rated at 40mA (I think, I’ll measure when I get it). The ANT+ is around 4mA (I think, It very much depends on several factors). So really I’d need a few hundred mAh to run this. Not bad, but coin cells won’t cut it! A CR2460 might last 10 – 15 hours. Pathetic. Li-Poly it will be.

2) Wireless interference: The ANT+ sensors operate on a prescribed channel. I’ve heard of issues when 5 – 10 people have multiple sensors in the same location. I think the Bluetooth module has some more agility in channels than the ANT+, but this might still cause interference.

3) Unsecured: The ANT+ module isn’t really secure. It’s secured by the ANT+ network key that keep people from creating malicious devices. However, if I was to be riding along with a pro I could easily capture their data. The Bluetooth module has the same code to access it, “1234”,  which means Joe everyman with a laptop or cell phone could come by, connect and start messing up my data.

4) The ANT+ Communications and processing is now handed off to the host device! The laptop or mobile phone is the one that says “Here is the ant+ network key, channel, power output, etc” and it’s also tasked with turning the string of characters into the actual power numbers. I believe this is how the ANT+ enabled phones work already, but it means that the software program is responsible for reading the data as it’s transmitted and dealing with issues as they crop up


  1. Nice. I want to build one too, but I can not find a ANT+ Board like yours

    1. Sadly they stopped making this one, however Dynastream makes a FCC certified module. It's part number is ANTAP281M5IB.

      It's a little harder to work with as it's intended to be reflowed on a circuit board but I know many people (I've done this too) that have soldered wires to it.

      Dynastream just sent me some stuff needed to build my own API, so while I'm waiting on circuit boards I might look at this again.

      Link to digikey

  2. What about Ussing this one:

    1. I've been waiting a year for this chip, and it's great that it's out. However BTLE is not BT 2.0/2.1. This is already covered by the 4iiii's Viiiiva hrm that does all this translation already. I was mainly focused on enabling phones without BTLE. However, I've decided that by the time I could get this finished and implemented in Android that most people would have BTLE in their phones anyway and then the Viiiiva covers that off nicely.