Hi. I have built an interface between a Raspi 4 and an Alarm Panel with some extra add ons. The diagram below shows 3 circuits A, B & C.
Circuit A at the top has 8 inputs from the alarm panel (12v) and feeds them through 8 optocouplers (2 x 4 modules) - note the internal 3K resistors and the common output ground. The normally high panel inputs are held low into the Rasp Pi.
Circuit B is a push button 5v input that feeds though an opto-coupler into the Rasp Pi
Circuit C is a 3.3v output from the Rasp Pi that feeds though an opto-coupler into a 5v relay.
Note that the circuits within the red dotted line are on a single piece of strip-board an share a common ground with the Pi
All 3 circuits work on their own but when I press the Ciricuit B push button then one or more of the 8 panel inputs into the Rasp Pi go high. I've had up to 6 fire.
I suspect it is something to do with the common ground but no idea how to fix it. Would one or more diodes help (at Z?) or is there something wrong with the design or if not, then maybe with the construction?
Help much appreciated. Thank you
Alan
Wiltshire
Circuit A at the top has 8 inputs from the alarm panel (12v) and feeds them through 8 optocouplers (2 x 4 modules) - note the internal 3K resistors and the common output ground. The normally high panel inputs are held low into the Rasp Pi.
Circuit B is a push button 5v input that feeds though an opto-coupler into the Rasp Pi
Circuit C is a 3.3v output from the Rasp Pi that feeds though an opto-coupler into a 5v relay.
Note that the circuits within the red dotted line are on a single piece of strip-board an share a common ground with the Pi
All 3 circuits work on their own but when I press the Ciricuit B push button then one or more of the 8 panel inputs into the Rasp Pi go high. I've had up to 6 fire.
I suspect it is something to do with the common ground but no idea how to fix it. Would one or more diodes help (at Z?) or is there something wrong with the design or if not, then maybe with the construction?
Help much appreciated. Thank you
Alan
Wiltshire