On April 6, 2005 12:51 am, liam . wrote:
> All,
>
> I'm trying to workout how to approach the design of a Bike Computer.
> This is not a computer for a bicycle but rather for an exercise bike
> that will interface with a real computer.
>
> The exercise bike already is fitted with a reed switch and so a sense
> of wheel rotation is known. I'm of split opinions at the moment
> however at the moment on whether to use a PIC onboard to work out
> stats like speed, distance, RPM etc and then send this to the
> computer or to only send the wheel telemetry to the computer and use
> software on the computer for processing. How would others do it ?

Unless you are going to display stuff at the bike, you are probably best 
to send raw data to the computer, which can then graph/plot or do 
whatever with the raw data. If you compute values at the PIC, you may 
have to uncompute values at the computer to interpret some missing 
values that get lost in computation (and didn't seem necessary to send 
then).
You also mentioned a time factor, so keeping it simple also gets the PIC 
part out of the way quick.

> The concept has been suggested that multiple bikes are connected to
> the same computer for telemetry recording which also would influence
> the decission of where to process and how to connect.

You can bundle telemetry for burst transmission, such as multiple PICS 
talking to one link, or IR transmission with repeat-due-to-error.  This 
gets cables out of the way.

> The obvious solution for connection was RS232 however most laptops
> dont have serial anymore so then its a case of embedded USB support
> or use USB dongles. Which would be better ??

Some laptops have IR, otherwise RS232-to-USB converters are cheap so you 
can stay with RS232.
You can still put several of your PICs in parallel on an RS232 line.
Use something like a resistor pull-up on your Computer RX line and let 
each individual PIC pull-down the RX line to make zero bits.
You would have to figure out when each PIC TXes data because each one 
would have to send during it's allotted time-slot.
Just keep your TX speeds low, like 300bps because you are using pull-up 
resistor type 1bits versus actual RS232-type drivers which would drive 
the bits high or low.

> This is a very low budget project and I wanted to be able to get this
> working with a minimal of components in a short time.

You could probably use the RS232 line at the computer to power all the 
pics for the multiple bike readers. The activity required by the PICS 
to compute raw data would be very low, so the PICs are mostly idle.
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