relay first timer

How Relay works and how to control it
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mickoz
Posts: 6
Joined: Sat Jun 27, 2020 2:19 am

relay first timer

Post by mickoz »

I can’t find a wiring diagram for the crowpi and blew a LED by connecting it directly to terminals 2 and 3 of the relay without putting a resistor into the circuit because I don’t know what voltage there is across the terminals or what voltage i should be putting on a LED. I have relay version 2 on my crowpi and watching v2 of the video i should have used a motor rather than a LED and wired it through the relay to a VCC and GND pin, but there is no diagram of this that I can find and video is not too clear on the detail. Any tips?

g7jjf
Posts: 11
Joined: Mon Apr 06, 2020 1:19 pm

Re: relay first timer

Post by g7jjf »

I only have a rev 1 board and not the rev 2 but I have found an excellent article on wiring a LED to a relay which you may find useful as a starting point. Check out https://osoyoo.com/2017/06/28/raspberry-pi-relay-led/

mickoz
Posts: 6
Joined: Sat Jun 27, 2020 2:19 am

Re: relay first timer

Post by mickoz »

I found the problem. The v1 relay doesn't carry a voltage like the v2 relay does, which I knew. The points not made clear in video or docs are these:

1) Although Elecrow posted a relay video v2 on YouTube, the only difference between the two videos is a superimposed whiteboard in the bottom right of the video showing the new wiring setup. So what the narrator says and the video of the wired-in motor have not been amended and need to be ignored. I only picked this up after watching the v1 video and realising that it was exactly the same video. Very misleading!

2) The diagram of the relay in the v2 video is upside down with respect to the viewpoint you have when viewing the CrowPi from the front. (And with the lid where it is, you can't really view it from the back!)

3) The most important point. In v1, power is taken from the pins in the bottom right of the CrowPi labelled VCC and GND, which gives you 5V, so I assumed that the V2 relay would be wired to give the same. Wrong. I just bought a multimeter and tried it out. VCC and GND give you 5.2V but the relay must be wired direct to the power supply because it gives you 12V. If you wire the small electric motor supplied directly to this as directed by the diagram in the video, without any resistors in the circuit, it draws too much power and the Raspberry Pi shuts down.

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