RE: How to detect external switch status

Former Member — Mon, 04 Mar 2013 15:27:09 GMT

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

RE: How to detect external switch status

DAB — Tue, 26 Feb 2013 20:49:58 GMT

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