Group Actions
Engagement
  • Author Author: Former Member
  • Date Created: Date Created
  • Views 668 views
  • Likes 1 like
  • Comments 2 comments
Related
Recommended

How to detect external switch status

Former Member

I have got a project to design a circuits to control and detect an external electrical circuit. The project should complete these functions as I list below.

 

1. I cut off external circuit and connect two broken wire terminal to a relay in my board to realize turn off/turn on external circuit. It is not a problem.

2.  Detect external circuit loop status (Open/Close)

3. Detect the relay status in my PCB(On/Off)

4. All my controll circuits should be isolated to external circuits.

5. The voltage of external circuit is 24VDC/24VAC

 

 

Please review attachement.  K1 is a relay of my project. Besides k1, I have to add a detection circuits to detect S1 status(if it is open/close).

All my circuits should be islolated to external circuit. The basic rule is cheap and reliable.

 

 

Best regards

Jim

Attachments:
image

  • Hi DBA,

    Thank you very much for your response. In fact, besides isolation, cost is another very important factor that we have to consider. An important thing is that the current of the external circuit is not very big(500mA), so we couldn't use hall effect components and if we use an isolated current sensor, we have to add an amplifier and it is too complex for the detection circuit.

     

    I use the chip LDA110S (that has about 1ma forward current, it is a little big and would affect external circuit,I connected LDA110S cross relay contact with a seriel current limitation resistor). Besides LDA110S, I have to add another circuit to detect the external circuit status when the relay on board is closed.

     

    Best regards

    Jim

  • Hi Jim,

     

    I would go with optoisolators to do the detection.  They will only turn on when current is being pulled by your external device, plus they isolate your board from any spike issues with the external load.

    The same goes for your relay.  The same current that flows to activate the relay would power the isolator, giving you a signal only when the relay is in use.  The trigger logic is simple and you eliminate a lot of potential issues with current and load variances.

     

    Just a thought,

    DAB