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Electronics => Beginners => Topic started by: Sultanpepper123 on October 22, 2019, 07:23:52 pm

Title: best practices in detecting relay contacts status
Post by: Sultanpepper123 on October 22, 2019, 07:23:52 pm
Currently i'm experimenting with 12VDC energy meters latching relays and at least for me the feature of detecting status of contacts ( required by some clients ) which is built in as in the diagram below is quite interesting. Now i need to interface it to a microcontroller safely. At the top of my head i may think of using an optocoupler but my understanding is i need to isolate the grounds ? thus making the design a bit pain in the kneck, is this the only feasible method or are there other approaches ?. enter image description here

(https://i.stack.imgur.com/PrsDo.png)
TL;DR pins 4 and 5 switch on / off depeding on status of relay, how do i sense/ measure status of the latch with those pins?
Title: Re: best practices in detecting relay contacts status
Post by: GerryR on October 22, 2019, 08:50:34 pm
If the 4,5 contacts are isolated, why not tie one contact to a pull-up resistor and feed the other to a micro input.  If the micro inputs are already pulled up, then tie one contact to the micro common and the other to the micro input of you choice.  The change of state tells what position the relay is in.  :-//
Title: Re: best practices in detecting relay contacts status
Post by: Sultanpepper123 on October 22, 2019, 09:01:46 pm
Quote from: GerryR on October 22, 2019, 08:50:34 pm
If the 4,5 contacts are isolated, why not tie one contact to a pull-up resistor and feed the other to a micro input.  If the micro inputs are already pulled up, then tie one contact to the micro common and the other to the micro input of you choice.  The change of state tells what position the relay is in.  :-//

Thanks for the suggestion, looks simple enough. What made me worry at first whether there was any EMI or transients i should worry about.
Title: Re: best practices in detecting relay contacts status
Post by: mikerj on October 22, 2019, 09:20:53 pm
Quote from: Sultanpepper123 on October 22, 2019, 09:01:46 pm
Quote from: GerryR on October 22, 2019, 08:50:34 pm
If the 4,5 contacts are isolated, why not tie one contact to a pull-up resistor and feed the other to a micro input.  If the micro inputs are already pulled up, then tie one contact to the micro common and the other to the micro input of you choice.  The change of state tells what position the relay is in.  :-//

Thanks for the suggestion, looks simple enough. What made me worry at first whether there was any EMI or transients i should worry about.

Not from the isolated contacts themselves.  Avoid routing the connections between the contacts and the microcontroller close to, and parallel with the switched side of the relay coil.
Title: Re: best practices in detecting relay contacts status
Post by: Sultanpepper123 on October 22, 2019, 09:38:00 pm
Quote from: mikerj on October 22, 2019, 09:20:53 pm
Quote from: Sultanpepper123 on October 22, 2019, 09:01:46 pm
Quote from: GerryR on October 22, 2019, 08:50:34 pm
If the 4,5 contacts are isolated, why not tie one contact to a pull-up resistor and feed the other to a micro input.  If the micro inputs are already pulled up, then tie one contact to the micro common and the other to the micro input of you choice.  The change of state tells what position the relay is in.  :-//

Thanks for the suggestion, looks simple enough. What made me worry at first whether there was any EMI or transients i should worry about.

Not from the isolated contacts themselves.  Avoid routing the connections between the contacts and the microcontroller close to, and parallel with the switched side of the relay coil.

Really appreciate the help and sharing your thoughts.  :-+

Quote from: GerryR on October 22, 2019, 08:50:34 pm
If the 4,5 contacts are isolated, why not tie one contact to a pull-up resistor and feed the other to a micro input.  If the micro inputs are already pulled up, then tie one contact to the micro common and the other to the micro input of you choice.  The change of state tells what position the relay is in.  :-//

Again thank you sir for the help .  :-+