> > Maybe Im just too thick to be working on this because Im totally lost. No. Obviously not "too thick". BUT. It is liable to help if you - Take note of the technical answers that you get. - Try and assess which are liable to be useful ones (generally but not always assessable from detail provided, part numbers or general descriptions, care of explanation, technical persistence of answerer over several questions etc) - THEN try and understand such answers. - THEN answer any questions that such answerers have asked. - THEN ask more questions as/if required. Note - you tend to fit the following 'model' to a reasonable extent. Note that this is NOT a personal criticism per se, as it is common enough with people dealing in things a bit beyond their areas of expertise. It's useful to you and others if you can short-circuit this process if possible. Newcomers often: - Tend to seize on parts of answers that seem good to you without taking the whole answers, and - When people ask good questions, tend to answer them selectively. - As a consequence - don't get where they are trying to go nearly as quickly as if they'd 'coopererated', - Get more confused than is strictly necessary and - Tend to wear out the people trying to help. The 'flip side' of avoiding this is you have to trust the 'experts' somewhat, they have to be polite and helpful and you need to decide which experts really are experts :-). In a group of several they will be somewhat self correcting. Where you read YOU below expand it mentally in each case to read " you (as is common enough amongst beginners, so we understand, but we'd appreciate you learning from the experience) > > I dont see why I cant use strobing to arrange the 90 wires into 9 > > columns of 10 and at each crosspoint put an AND gate transistor. > 90 transistors =A0& 19 pins > vs 12 ICs that are cost of two transistors and 3 pins Yes. Transistor and gates are an option. An AND gate would eg consist of 3 base inputs which are all -ve wrt ground to turn the transistor off . eg 5 VDC local supply with +5 to gnd and loacal-gnd =3D -5V. Logic high =3D ground =3D 1 Logic low =3D -5VDC wrt ground =3D 0 Row and column mux are normally high. Inputs are 0/-50V. Row & column inputs =3D sat 1 diode each. -50V input =3D 1 resistor to -50V and 1 resistor to logic high as pullup Per gate =3D transistor + 2 diodes + 2 resistors. (90+180+180 all up) + some common mux components. + 19 PIC pins "My" opto solution used 90 opto ICs (or 45 duals or 23 quads) and AFAIR NO other per channel parts, + required some drive components. + 19 PIC pins A serial shift register arrangement needed 12 x 8-input SR ICs (which are very low cost) + 180 resistors + 3 PIC pins. 4051 transmission gate solution needed similar but more PIC pins. The 4051 solution has the advantage that you COULD use an ADC and measure actual input voltage, if you cared. (you don't, probably). Which solution is best for you is unknowable to "us" because" you did not provide enough detail and didn't answer questions relating. What is an acceptable cost target? Are you comfortable with SMD, ICs, soldering, many resistors, ... . etc. If we know what you know and what your real objectives are then we can better help. We'd like to. If ease of manual assembly was the aim I'd look hard at the opto solutions. For overall convenience and cost and size and ... I'd lean towards the shift register solution. etc Russell > > -- > 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