I am planning to build a speedometer for the model railroad. It should
measure the actual speed of a train via a sensor on the axle of a wagon (via
a white spot on the black axle and an IR fork lite barrier). The impulses
should be transmitted via ?? to a local base station, max. distance around
30m (90 ft). The power for the barrier and the ?? transmitter will be
delivered from the rails via a LT1073 (Micropower DC/DC converter) working
as a regulator for 5V and a 1F Gold Cap.

In the local station should be the ?? receiver, a PIC for counting and
calculating the "real world speed" (conversion from actual speed in scale
1:160 to speed in 1:1) and presentation on a LCD.

The PIC part is clear - counting the received pulses for a specified time,
calculating the speed and multiply with the scale factor for real world
speed and show the calculation on the LCD. An indication if the link is OK
should even be included and shown on the LCD.

I am thinking about a good method to transmit the pulses to the local
station - either via RF or IR. The advantage of RF is that there has to be
no line of sight between transmitter and receiver, the disadvantage that a
RF transmitter is a bulky element that is maybe not fitting in the space of
a 1:160 wagon. In addition I have no idea if there are small, simple and
cheap integrated building blocks at the market. IR looks much easier but
there has to be a line of sight between transmitter and receiver, in minimum
the reflections from walls or ceiling has to be strong enough to decode the
pulses safely.

So I have a few questions - what do you think is the better method for
transmitting the pulses, is there integrated RF equipment on the market
which is simple to use, cheap and small enough, does somebody have
experience with transmitting simple pules via around 30m max...

Last but not least - the maximum number of speedometers is very small (one
for me, one or two for collegues in our model railroad club).

I really would appreciate your thoughts and help.

Regards
Enrico




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