IpWatts is a rather specialist application to allow you to log the data from multiple bicycle power sensors simultaneously into a single file. inspired by a request from DC RainMaker in this blog post I cloned the IpPeloton front end and tweaked the IpSensorMan API to get something going in fairly short order.
If you use this application and publish results I would ask you to acknowledge the use of the app and ideally link to IpWatts and IpBike in Google Play. Please feel free to email me with any issues. I consider this to be beta until it has had some more real world use, which given the specialist nature of the app may take some time.
You will first need to pair the sensors manually with IpSensorMan. Just go Start Ant then Search sensors. If there are multiple sensors active then go search sensors again to get another one open. You really want to try and start them up one at a time though if possible so you can be sure which is which. You can press on a sensor in the list and then name the sensor to make it distinguishable.
Having added the sensor just open IpWatts it will look for a single instance of the standard biking sensors + heart rate. Data from these is displayed at the top or left. It then opens as many other power sensors as it can, you get a list of the sensors with the current power value. You can calibrate a sensor by pressing it in the list. Once all the sensors you want are in the list just press start recording. When your done press stop recording. After pressing start you can leave the main IpWatts screen and recording will carry on in the background.
The logged file will be on the sd card in /Android/data/com.iforpowell.android.ipwatts/files/internal_logs/ the file name will be unique.
The data consists of a time stamp column followed by speed, cadence and Heart rate. Then for each power sensor 4 columns. First the watts value, then the accumulated Watt seconds value, then the pedal % or 127 if it is not available. Finally there is a 1 or 0 to indicate if data was received in this second, this should allow you to see if there are bad reception issues. If data is not received then it is latter filled in with the next good value which should be the average over the bad reception period provided the gap is not too big. For the accumulated Watt seconds the value will just stay the same during bad reception but then catch up on a good event. The pedal % can not be relied upon with bad reception you just put in the last value. The speed is assuming a 2070mm wheel and is in m/s so you probably want to do some spreadsheet work to convert it to your desired value.
There is a limit of up to 4 power sensors with the current version. You should be able to have IpBike active simultaneously with IpWatts once you have the recording started.