[arjoll]

This next one is a bit rough. Its an interface into our telemetry unit for another site.

(unfortunately the main telemetry unit died after a power cut so we're flying up tomorrow to replace it but that's another story)

The EDAC telemetry unit sends and received SMS messages for telemetry. Its inputs can be either analogue 0-5V, analogue 0-20mA or digital.

Our equipment puts out a mixture of signals - the STL receiver is a straight NO or NC relay contact so that's easy. The RVR gear is more difficult - alarms are 15V, forward power is something like 0-1.4V and reflected 0-1.6V. Rather than use resolution I decided to scale these voltages up.

The board is a lot messier than I'd like, but it was put together in a hurry and I changed my mind about a couple of things during construction. I also forgot some basic things - like pull-down resistors on CMOS inputs - which I know you have to have, and thought of several times, but never actually left room on the board for them - hence the numbers of resistors soldered to the D connectors!

This unit is due for a rebuilt in a 1U rack case sometime over our summer.

Circuit-wise this uses a 4050B to buffer the +15V signals to a +12V rail for the relays, more scrap BC107's (probably didn't need them but thought I'd over-engineer) to interface to the RS screened reed relays, and an LM324 op-amp to scale the low DC signals up to 5V FSD.