> Ive been doing some research into possible solutions and have found > references to =A0a MAX4626 "analogue switch" which to me looks like a > solid state relay - it says its the size of a grain of rice. Only if you use REALLY big fat rice. About 3mm long in typical packages. I'll bring your question up to here > Does that sound reasonable? No. It sounds like you have looked at a data sheet as you know about there being a COM pin, but maybe not. There's an extremely good datasheet search engine here - one of the best. Doesn't list everthing, but more than most, is easy to get at the datasheets, unlike some., also gives an idea of typical proices and availability and more. They seem to have an ulterior motive :-) www.digikey.com Data sheets of your nominated IC and some friends are here - are here http://datasheets.maxim-ic.com/en/ds/MAX4624-MAX4625.pdf http://pdfserv.maxim-ic.com/en/ds/MAX4626-MAX4628.pdf For the '4626 it says - Analog switch range =3D 0 - v+ - V+ =3D 5V. AND if you turn off V+ as a means of deselecting an IC then V+ =3D 0 so Vin max =3D 0 so :-(. To use them you will need to divide (or otherwise reduce) your input voltage FIRST so you will need probably 2, just possibly one and perhaps 3 or 4 components per input. And your grains of rice probably cost over to well over $1 each, have to be mounted etc. If you want an idea that would perhaps allow a single divider see "SINGLE DIVIDER?" at end. ____________ A very major "problem" here is that you have not told people what you are trying to do in adequate detail. Questions have been asked and some but not all answered. It MAY be that your application is so secret that you don't wish to tell people what it is. BUT if not it would probably help immensely if you provided more detail. eg - re the input telephone lines? - Are they able to be "unbalanced" by sampling while measuring and/or by the measuring system when not measuring (eg tapping even a large value resistor to ground from one leg of a telephone pair at all times will cause audio imbalance and, usually, hum induction. - Is the voltage ground referenced and if so is it +ve or -ve wrt gtound? Or is it floating? - If floating - one sort of isolation voltage is needed and/or how much may it float away from 'ground' by. - Is there a cost budget, size budget, other budget? - Is this a one off or many off. - Is there a lower limit to the acceptable sampling rate. (Per uS, per ms, per second, per day , ...) All or some of the above MAY seen unnecessary questions and they MAY in fact be so. But, probably not. "Just telling us" what you are really trying to do in as much detail as reasonably possible would greatly aid us in aiding you. Probably. Given all the specs there are probably tens of people on this list who could give you extremely good cost effective answers. ___________ SINGLE DIVIDER? Blame Jinx for the inspiration. Assume inputs are 0/+50V wrt aq common ground. Other polarities and relationships can be dealt with similarly. 90 optocouplers. PIC drives optos in row/column arrays. Opto collector per input. Combine emitters Monitor emitters as optos are turned on either one at a time or in groups. Note that the title has a ? in it. Turning on an opto with an active high collector input will pull the common emitter rail high to "above" any other 'off' collectors. This may/will cause design issues which have to be dealt with. Doable - but more details re overall system is required. Putting a single resistor in each input lead and sharing a common output resistor - or a semi matrixed array of outputs, would probably fix the above problems. There will be other ways once the REAL question is known.m Also, leakage from 90 optos needs considering. These may do 40 cents each in 100 quantiyty. Others are cheaper to much cheaper. 80 V rated. About ? twice as latge as your transmission gates - but these would work. http://media.digikey.com/pdf/Data%20Sheets/Sharp%20PDFs/PC357NJ0000F.pdf You can go to 2 or 4 per package. These cost about 20cents per opto channel in 4 per package at 10 up rate. SSOP etc available. http://media.digikey.com/pdf/Data%20Sheets/Lite-On%20PDFs/LTV= -8x6.pdf Haven't gone into any detail on how ell would work (except Vout max) as real problem isn't known. _______________ A similar arrangement could be considered with multiple FETs or bipolar transistors as switches and some form of matrixed gate/base drive. The optos are cleaner. The above using reed relays would work well BUT expensive. > What Im contemplating is using 90 of these arranged in a matrix with 9 > columns and 10 rows per column. =A0Each column would share an output pin > from the PIC which I shall refer to as "column select" This would be > wired in parallel to the COM pin of the MAX4626. =A0The IN pin would go > to the wire I want to sample which has a voltage divider on it to drop > it to 5v. > > The PIC then tests each column in turn by switching on the appropriate > column select wire, thus applying 5v to the COM pin of all the > MAX4626s in that column. =A0If the wire being sampled is live it will > put 5v on the IN pin and the solid state relay will close. =A0The > prescence of 5v on the NO pin of the 4626 will indicate the wire > sampled is live. =A0This will allow me to sample the 90 wires using > only 19 i/o pins on the PIC. > > > Does that sound reasonable? No, again :-). Real problem please. 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