Andrew We are homing in on your requirement. BUT would you PLEASE write us a small essay - few paragraphs should do - describing EXACTLY what you are trying to do. Each little extra tidbit has allowed us a slightly better idea, but there is still some way to go. You have several centuries of engineering experience hanging on your every utterance. PLEASE now try and make best use of it by now providing a clear picture eg the following MAY adequately describe what you are trying to do, and may not. A. There are 90 reed relays. The coils are driven with [ +50 | -50 ] volts relative to earth via relay contact so that on the coil there is either [+50V | -50 ] V wrt ground when the coil should be activated or a resistive coil to ground when the coil is deactivated. The aim of the project is to be able to electronically monitor the 50V signals to establish when they are or aren't applied applied. The 50 V signals are i for control purposes only and do not form part of an actual speech circuit. (ie The relays are/aren't involved in switching speech but the sign= als concerned do not have speech voltage on them). OR ii also have AC speech signals on the same circuit as the DC 50V. (ie as per standard telephone circuits) The reed coil resistances are [xxx ohms | unknown] It would be adequate for the PIC to be able to read the state of the 90 lines once every [ ms | 100 mS | 1 second | 10 seconds] The 90 channels on electrosensitive paper mentioned i Were what was originally there and I wish to replace them with a PIC moni= tor. OR ii Were not originally driven by the system - I wish to use the PIC to drive them. Overall: A historical status monitoring unit drove a 90 channel electrosensitive paper recorder using 90 reed relays activated by +50V signals relative to ground, applied by relay contacts. The aim is to dispense with this recording unit, monitor the 90 lines with a PIC based circuit and process and act on the signals accordingly. etc ___________ SO, Andrew, your turn. If you can be at least as detailed as above then we can probably provide some very good answers. Failing to provide this level of detail is wasting a lot of people's time unnecessarily. (That's not a complaint - just advice re asking good questions). It will be a complaint if you now don't do it :-). Russell On 30 May 2010 08:51, Bob Blick wrote: > > On Sat, 29 May 2010 20:23:19 +0100, "Michael Watterson" said: > >> sounds like it is drivers for 90 pin parallel head printer, not voice >> lines directly (but who knows?) >> So common ground, no opto isolators needed >> use resistor divider on each driver pin/pen to convert to 5V. Since it >> might not be exactly 50V, a resistor divider to reduce volts to 6V out >> from 48V in =A0and 4.7V zener . > > Unless it's positive ground like lots of old phone company stuff seems > to be... > > Hey, Andrew, have you reverse-engineered the part of the circuit you > need to monitor? Where is ground in reference to the 50 volts(positive > or negative)? Or, even better, is there some driver for these > pen-thingys that is driven with a logic-level signal? That would be LOTS > easier to monitor. I don't know what your level of electronics expertise > is, but the more you know about the problem, the simpler your solution > will be. > > Cheerful regards, > > Bob > > -- > http://www.fastmail.fm - Access all of your messages and folders > =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0wherever you are > > -- > http://www.piclist.com PIC/SX FAQ & list archive > View/change your membership options at > http://mailman.mit.edu/mailman/listinfo/piclist > -- = http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist