When starting a new project, RTFM first!

How do you turn this

mag trainer

into this?

Computrainer

Short answer is you don't, you order a Computrainer from Racermate, they charge you around $1600 and then you sell the old one on Craig's List.

Long answer is you don't, but I think you can get some of the same features by automating the old mag trainer. Equipment list is:

• Arduino with USB or XBee communication to a PC for data logging/display
• Reed switch speed and cadence pickups, suitably debounced
• Polar receiver from Sparkfun
• Stepper motor and stepper motor driver, also from Sparkfun
• Some hardware, especially to adapt the stepper motor to the mag trainer resistance adjustment cable
• Software for the PC (some coding required)

Goals are:

• Estimate average and instantaneous power output, based on trainer documentation
• Graph power vs crank position
• Automated resistance adjustment for training sessions
• Record HR, speed, cadence, power results for session
• I'll pass on all the fancy graphics (other riders, etc) and dead accurate power values - the homebrew solution should at least be consistent, give me some better training feedback, and cost under $200 (my development time not included. Could be packaged and sold I guess, but at least for now that's not the main goal.

The stepper motor and driver are the big question marks for me - I've never used either before, and I'm not sure how much force I'll need to pull the resistance cable - so I decided to start there. And promptly released the driver board's magic smoke. I pulled a wire from the motor driver output side while the motor was powered and fried the driver chip. Had I read the warning on the web page (not even buried at the back of the datasheet!) I would have known better 

Note: Do not connect or disconnect a motor while the driver is energized. This will cause permanent damage to the A3967 IC.

How many times have I told students "DO NOT MESS WITH THE WIRING WITHOUT REMOVING POWER!"? At least I have another example of why you need to do that.

So, development of the resistance adjustment is stalled while I wait for a new driver board. Guess I have to start with the speed/cadence and heart rate side first.

RTFM, RTFM, RTFM....