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GPIO interface circuits

tm14

I you mentioned doing a episode on GPIO.  I am interested in GPIO interface circuits.

 

I need to upgrade my old home automation system.  It is an old PC with data acquisition ISA cards.  I use one A2D with auto range to sense whole house power usage with two current transformers.  I have 16 optically isolated inputs connected to wired magnetic window and door contacts separately powered at 5V.  I have several relays to control HVACs.  I have many x10 modules to control lights, appliances, and irrigation.  I also have a voice modem to call on intrusion and to receive calls to allow remote control by phone, or locally with local phone system at door entry.  The PC runs with only 1MB memory,  DOS, Quick Basic, and my custom program that handles various schedules and events.  This is really old technology but it still works well.

 

I want to bring it into the 21st century running under Linux.  I could use a Raspberry Pi, plug in a relay board, but I have not found any good ways to do the A2D and digital inputs with GPIO.  I need isolation, protection against high voltage and static discharges from long wire runs to window/door sensors, and A/C and RF noise tolerance.  I also need help in interfacing with the A2D and DIO devices in Linux.  I would like to use GAMBAS, but C, Python, and maybe even BASH would be okay too.  The system runs 24/7 so power usage should be minimized, but functionality and expandability should not be compromised.

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  • Most of the sensors going into your ISA cards are single bits- you could use the Pi's GPIOs to read and/or write them, optoisolator chips aren't that expensive, for instance this one, about $10 for all 16 channels.  Relays to control HVAC can be controlled through optos to a ULN2803, and the current sensor transformers could be read through an Arduino.  Just measure the V/A that the transformers output with a multimeter and calibrate.  I'd bet one is a voltage sensing transformer and the other a current sensor, so you can measure power factor.

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  • Most of the sensors going into your ISA cards are single bits- you could use the Pi's GPIOs to read and/or write them, optoisolator chips aren't that expensive, for instance this one, about $10 for all 16 channels.  Relays to control HVAC can be controlled through optos to a ULN2803, and the current sensor transformers could be read through an Arduino.  Just measure the V/A that the transformers output with a multimeter and calibrate.  I'd bet one is a voltage sensing transformer and the other a current sensor, so you can measure power factor.

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