Its sort of telephones but not conventional phone lines. Its to go into a reed relay based telephone switch from the 1 Sent from iPhone On 29 May 2010, at 10:19, RussellMc wrote: >> Ive been doing some research into possible solutions and have found >> references to a 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 = 0 - v+ > - V+ = 5V. > > AND if you turn off V+ as a means of deselecting an IC then V+ = 0 so > Vin max = 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. Each 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. The 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. If the wire being sampled is live it will >> put 5v on the IN pin and the solid state relay will close. The >> prescence of 5v on the NO pin of the 4626 will indicate the wire >> sampled is live. This 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. > > > R > > -- > http://www.piclist.com PIC/SX FAQ & list archive > View/change your membership options at > http://mailman.mit.edu/mailman/listinfo/piclist > > ______________________________________________________________________ > This email has been scanned by the MessageLabs Email Security System. > For more information please visit http://www.messagelabs.com/email > ______________________________________________________________________ -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist