I'm currently using NodeRED to interact with the GPIO pins of my RPI4 board. All works pretty well, but when I'm rebooting my RPI I have a very short signal pulse to the relays that are connected to the GPIO output pins. Which means that strange things happen in my home automation (curtains closing,…

[image] rik1984: The question is still whether this will fix the spike You could presumably add debounce logic to the PLC that required a certain width input pulse to react, and set it greater than the spurious signal.

The PLC is fully wired-in in the house (previous owner) and is a very stable domotica system (Siemens Logo!). But no internet connection or possibilities to extend with wireless devices. That is why I started interfacing with a RPI a few years ago. The is a newer Logo hardware on the market with a …

Thanks @markost , I'll try this wiring. It feels a bit strange to connect the GND of the external power supply to the GND of the RPI. But I think i've read that more often so I'll try. The question is still whether this will fix the spike, but at least it sounds like a correcter wiring of the relay…

[image] rik1984: But no internet connection or possibilities to extend with wireless devices. The question was whether it has a serial port for serial modbus.

Haha I like your thinking, I immediately implemented it and it is pretty effective! It's not solving the cause, but it works!! No serial modbus possibilities for this version btw I'll do some more fundamental tests by rewiring the relays etc later. It will take a bit more time, but I'll keep this …

Having considered again the circuit in the relay board (as seen in the link you posted in post 29) I realise I have to eat my words. The ground connection is, in fact redundant. The wiring you originally had is correct.

Thanks for reconsidering. The only ambiguity I still read is whether or not to connect the GND of the external power supply to the GND the relay board AND the GND of the GPIO In the picture below the last one (GND to GPIO) is left unconnected: [image] And what the possible consequence is of NOT c…

In my experience, both as a Field Engineer and designer of electronic hardware for control systems, I have seen problems when the ground of a 'slave device' is not connected to the ground of 'the master'. If they are connected, the 0V are at the same level, therefore the intended signals are at th…

[image] mudwalker: I have seen problems when the ground of a 'slave device' is not connected to the ground of 'the master'. To understand this it is necessary to understand the circuit in the relay board. The part connected to the Pi is very simple, it is just a photo diode in the opto isola…

Just one question for the mentioned setup (+5V on top side of optocoupler, instead of +3.3V): when the RPi gpio is in HIGH state, we have +3.3V at the input of the optocoupler. On the other side of the optocoupler we have +5V. So, the potential difference is 1.7V and correct polarity... Is this…

Strange signal spike to GPIO pins at startup of NodeRED (Pigpiod)

General

Colin 18 May 2023 08:36 51

The connections shown in the image are correct.

However, as I said earlier, I have had no problems using the 5V from the Pi to drive the relays too (an 8 relay board in my case). To do that, remove the separate supply, put the jumper back in, and connect GND on the pi to GND on the relay board.

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Strange signal spike to GPIO pins at startup of NodeRED (Pigpiod)

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