Help with 4ch relay for telescope control. - Page 1
Forum section: electronics / beginners

author: Gd5150
author_rank: Newbie
timestamp: March 17, 2020, 05:40:16 pm
content: Hello. I built a small adapter using a 12v 4ch relay board. It takes the input from the ST-4 output on a guider camera, adapts the signals to control the pre-computerized hand control from my Celestron SuperC8.On the board there is an option to use an external 12v power supply to power the optoisolators, which I’m using. Then there’s the 4 inputs for relay signals, vcc power input (which I’m not using because I’m using external power supply) and the ground.My question is there’s only one ground output on the board. There’s an input for the 12v power supply but no ground. The ground is next to the control inputs signals.The input control signals come from a camera that’s a different source that than the power supply. The control signals have NSEW and a ground. The 12v power supply has 12v and a ground. But the board only has 1 ground output which goes to the camera. So how do I ground the back to the power supply?I’ve attached an image of the relay board and my wiring diagram.Any help is greatly appreciated!

author: madires
author_rank: Super Contributor
timestamp: March 17, 2020, 06:11:37 pm
content: I've looked for more info on the relay board and foundhttp://wiki.sunfounder.cc/index.php?title=4_Channel_5V_Relay_Module.The relay board is designed for 5V, not 12V. The optocouplers' inputs are meant to be driven via an "open collector", i.e. when switched to ground the relay is powered.

author: Gd5150
author_rank: Newbie
timestamp: March 17, 2020, 08:18:14 pm
content: Thank you for the reply. The one I’m using is 12v. Here’s a photo of my actual relay board.

author: Gd5150
author_rank: Newbie
timestamp: March 17, 2020, 09:10:14 pm
content: Here’s the sellers description on the relay board. Sorry it’s limited on these.4 Channel Relay Module:1. Working Voltage: 12V2. Channel: 4 Channel3. Module: 12V 4-Channel Replay interface Board4. 12V 4-Channel Reply, interface Board, and Each one needs15-20mA Driver Current.5. Equipped with High-Current Relay, AC250V 10A; DC30V 10A.6. It can be Controlled Directly by Microcontroller (For Arduino,8051,AVR,PIC,DSP,ARM,MSP430,TTL Logic).

author: Brumby
author_rank: Unknown
timestamp: March 17, 2020, 09:59:31 pm
content: Quote from: Gd5150 on March 17, 2020, 05:40:16 pmYou seem to be under the impression that all connections are one to one only. While this is often (but not necessarily) true with signal connections, it is less true with power connections and almost universally NOT true about "ground" connections.In short,typicallyyou connect all the "ground" wires to a single point. (This is a subject that deserves its own examination if you want to really get into it - but for your example, this should be fine.)(Also, I used the word "ground" in inverted commas, because it does not necessarily involve a connection to the dirt under your feet - but is almost always simply a 0V reference.)

author: Gd5150
author_rank: Newbie
timestamp: March 17, 2020, 10:45:30 pm
content: This is why I’m confused. The signals come from a camera being powered by a laptop. The 12v power supply is a separate battery back.Should i connect the ground on the battery and the camera to the 1 ground terminal on the relay board?I was afraid that might fry the camera.

author: madires
author_rank: Super Contributor
timestamp: March 18, 2020, 09:54:42 am
content: Are the signals from the camera 5V or 12V?

author: Gd5150
author_rank: Newbie
timestamp: March 18, 2020, 07:40:26 pm
content: They are 12v.