>
> Hi,
>
> I want to be able to read analogue voltages remotely using telemetry with a
> distance of say 200 metres between Tx and Rx.
>
> What is the cheapest and simplest method using a PIC for example ?

Well standard operating procedure dictates that you convert the analog to
digital as quickly as possible then work in the digital domain.

What's the voltage range of the analog signal? What precision do you require?
Lastly how often do you sample and how often must you update?

Your biggest problem is that 200m gap. Wireless is probably the most effective
method. But that's a long distance for the typical low powered transmitter.
If the straight line distance is unobstructed, with some high powered
optoelectronics and optics, you may be able to create an optical link.

Probably the most effective and unusual method is to interface to a cellular
phone and periodically dial updates to the base station. Could be cost
prohibative though.

May need to see about licensing some higher powered radios though.

The setup is the same regardless of the link type.

1) Sample the signal with and ADC onsite. If the signal can be conditioned into
a 0-5V range and you only need 8 bits of resolution, use an ADC PIC. Otherwise
get an external ADC perferably with a serial interface and attach it to the
PIC.

2) Use an appropriate modem to modulate the digital samples onto the link. For
example for the optical link this would mean driving a 38-40khz signal into
some high powered IR LEDs. If you stick to standard data formats and
frequencies you can use a UART in any form (software, builtin, external) to
serialize the signal.

3) On the other end, demodulate the signal. For example in the optical link
use one of the IR demodulating cans like the Sharp 1GU560 (?) sold at the
RatShack. Take the recoved signal and run it into the receive of a UART
(which at this point may be as simple as taking the signal and running it
through a MAX232 or equivalent to convert the 0-5V signal to -12 - 12V.

And voila!

Honestly though at that distance a data logger may be the best bet. Then you'd
go and fetch the data periodically. A serial EEPROM is a hell of a lot cheaper
than any type of link you can build to cover a 200m distance.

BAJ