Hi I am a programmer but new to electronics. I need to modify an existing data collection system to get data automatically from a number of presses. The local engineer can provide a 24 volt signal from each press when ever a part is made. The principle of reading a number of digital pins and passing the pin number when a voltage is detected to the serial port for my vb app seems fine. How would I reduce the 24 volts to 5 and would I just need a single wire from each press to a digital pin or would I need to ground also? I said I was new to electronics!
If the 24v supply is reasonably well regulated and doesn't have any significant electrical noise on it you could use a pair of resistors as a voltage divider to drop the 24v down to the 0-5V range. If it isn't clean you could use something like an optocoupler between them to isolate and clean up the signal. You would need a ground wire as well as the signal wire to each device. Perhaps the machines all have a common ground, but if not then the optocoupler approach would enable you to keep them electrically isolated.
The reason you would do it that way is because opto-couplers have been the interface of choice for industrial equipment to uProcessors since microprocessors have been available. I would add that the "upgrade" version of that interface is probably fiber-optic because it maintains the isolation but adds the benefit of really long cable runs.