hi all,

I race dirtbike enduros and can't find an enduro racing computer that satifies my needs, so I've been thinking of writing a program for a PDA instead.

the only thing I am really stuck on is a practical approach for receiving the signal from my odometer pickup. it's like any digital odometer setup, has a a magnet on the front rotor and a pickup on the brake caliper and generates a voltage spike when the magnet passes the pickup. I just need to figure out the hardware end of things and some of the low-end software to receive the voltage spike from the pickup and register it on the PDA.

any suggestions would be greatly appreciated.

 

You will need to firstly condition your signal to something suitable for the input to the pda...if the sensor is just a magnet and a reed relay, then you will need to detect the switch closing on each rev and calculate distance travelled by circumference of wheel etc...
Obviously unless there is a voltage difference you won't see anything from the switch, so you would need to supply the switch with a voltage...perhaps something like this...

+v - Resistor - PDA & SW - Gnd

+V o--/\/\/\-----o-----^---o { Gnd

+V Resistor PDA SW Gnd


If however the sensor is a coil with a magnet passing by it, you will need to clamp the voltage to some suitable value, and pass it through a precision rectifier etc before applying it to the PDA.

In either case, electrical noise will be your enemy, so you will need to make sure your signal is clean and stable.

If the sensor is actually a true digital instrument feed, your problems have pretty much been solved for you already. All you need do is take your signal, clamp it to a suitable voltage level and take it with a common Ground to the PDA.

The rest as they say are details...

I apologise for the crappy graphics...