I am currently trying to get my projects a little more automated but I'm not sure on this one. I have around 60 j111's I need to control with 8 PCF8574 I2C I/O expanders and a Propeller. The programing is done but I'm not sure how to convert the 3.2V out from the I/O chips too -15V, Would I be better off with an opto Isolator or just a transistor? What would be the best type of transistor? BJT, SCR, SSR, IGBJT, Darlington? and I would Like it in as few packages as possible, 8-16 outputs per chip if possible.
Off the top of my head: ULN2803 with its ground pin connected to the -15V. No clue if it' work, but it sounds feasible. BTW, why use IO expanders and not just shift registers?
I have them from an old project and thier just wasiting space on my bench:) Also I can do all of them from 2 pins off my micro.
Check this out, you can drive shift registers using only one pin :P
http://www.romanblack.com/shift1.htm
very interesting.... I've been using in some projects a 2-wire interface for LCD, but this is a nice way to get the same with only 1 wire.
Ya thats super cool trick for sure. But its not an I/O Expander its strictly an O Expander and its relatively slow at 3ms, I run my I2C buss at 500Khz, most all chips require at least 3 8 bit Signals to initialize them so its still tones faster on an I2C buss. For me though its still adding a pin to my project and 3 components where My I2C is using the same Buss as the EPROM and the same code to write to and read from the Buss. So Less code, less pins and way faster.
I will have to try this though, its a slick way of doing it