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I am building an irrigation system, and to make it short, I need to decouple the electric-valve to the Raspberry. I am so using the following relay. It works fine, but it is active LOW, for my use case I would prefer something that works the other way round (active HIGH). Can you suggest me one, considering that the Raspberry can just offer a 3.3 V?

Thanks

  • why do you need an active high relay? ...also, you cannot drive the relay directly, so the data pin voltage is irrelevant – jsotola Oct 11 at 20:13
  • I might be wrong, but it is not more efficient as I need to switch on the piloted circuit about 1 hour a day? – Edge7 Oct 11 at 20:18
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    Do not waste your time with this module. Hundreds of others have found they are unsuitable. They can be modified (by removing or bypassing the optocoupler) to make a active relay. – Milliways Oct 11 at 21:37
  • @Milliways Why are they unsuitable? I've used dozens of these modules and I find they are well designed. The Optocouplers are there to allow for smaller control voltages. Perfect for a 3.3V SOC used in the RPi – Omagasohe Oct 13 at 4:41
  • @Omagasohe They are so bad the Foundation has a warning. They are NOT "Perfect for a 3.3V SOC" - they NEED a 5 V supply, and risk damaging the Pi. The "protection" provided by the Optocoupler is delusional - and 3 relays requires 45mA to drive and the Pi GPIO is rated for a total of 50 mA max. – Milliways Oct 13 at 5:16
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Active Low relay boards are preferable in most electronic projects. These work by adding a Optical Isolator and a MOSFET between the relay and the Controller. The MOSFET wont be drawing current until you pull that line low. neither will the OPTO Isolator.

This is preferable since most IC's can sink(to ground) more current then they can source(provide current). this is also good since most microcontrollers and SOC's can provide pullups on their GPIO's. The pullups make sure state changes are intentional and you stay well with in safe limits for a SOC.

Your not directly driving the relay, your also not using current until you want to.

This is actually a well designed product. I'd be careful, Raspberry pi's aren't super tolerant to 5V. stuff.

You can mitigate this by removing the JVDC jumper, the JVDC Pin is the power line for the relay, supply that with 5V, and supply VCC with 3.3v

[http://wiki.sunfounder.cc/index.php?title=4_Channel_5V_Relay_Module][1]

Typical darwing at [1]: http://wiki.sunfounder.cc/index.php?title=4_Channel_5V_Relay_Module

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    I am, indeed, using it with the following wiring: "" You can mitigate this by removing the JVDC jumper, the JVDC Pin is the power line for the relay, supply that with 5V, and supply VCC with 3.3v "" The electrovalve is then working when I supply 0V to the GPIO pin which is connected to the IN1 pin of the relay, which means, most of the time I need to provide 3.3 V to the In1 Pin (as most of the time I want the electrovalve to be off) – Edge7 Oct 11 at 22:28
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    JD-Vcc is a bit tricky to use. You might like to read my TLDR workarounds to the following Q&A: (1) How to properly use a relay module with JD-VCC from Arduino/Raspberry? electronics.stackexchange.com/questions/505318/…. Cheers. – tlfong01 Oct 12 at 0:10
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    I would add that I have been using a board similar to this several hundred triggers per day, every day for a few months so I appreciate this answer. – MaxDZ8 Oct 12 at 7:47
  • I totally disagree with you!!! If it is active low or high is depending on the design! And most SOC can do pull up/down on GPIO, so again it depends on your design and preference So your facts are misleading... And what is the rambling about that RPi isnt 5volt tolerant, in this relay board it has no meaning, its a output from RPi that is controlling the relay board not the other way round. Please lets us keep to facts and not opinions! – Mats Karlsson Oct 12 at 10:52
  • If you power VCC with 5V, you'll be sinking 5V through the RPi GPIO. This isn't recommended. Also active low circuits is generally known as open collector. This has been around for a very long time. – Omagasohe Oct 13 at 4:32

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