Detecting mains into a CPU

Use an AC input module. Particularly for a test rig, this is the right answer.. they usually have an LED built in to show the state and sit vertically on your board saving space and provide isolation. They should cost around $10-15 each in small quantities.

You can build all that stuff on a board, maybe with a capacitive-resistive dropper and/or a sensitive AC-input opto-isolator, but why bother?

How about using a small disc capacitor instead of the resistor? Be sure to put a diode across the led for reverse polarity.

Tom

You can use a "wattless dropper" capacitor with a standard opto-isolator + reverse protection diode inverse parallel with the IRLED, you still have to use a series resistor to protect the diodes from spikes and surges.

I'd suggest between 1 & 2k for the resistor, start with 0.1uF and increase until it drives the IRLED reliably.

The capacitor must be X2 class rated for continuous connection across the mains - a common component found in most equipment as mains input filters.

You could also save component count by using AC input opto-couplers (saves the reverse protection diode) but they cost more.

He said cost is not important, right? So get a fluke 289 with the serial interface for each channel. When the job is over, hit ebay.

Are you useing a darlington output type? These typically have minumum CTR in the thousands. See.

All you need is 0.5mA to 1mA led current .

They dont give the fastest switching times but for 50-60Hz you dont need them.

Why not a simple *lamp* (240VAC, low wattage) on each output sensed with a phototransistor/diode/CdS? This assumes you can't replace the 240VAC with something "more convenient" (e.g., 5VDC)

Use inamps with high resistance dividers at the inputs. Yes, there will be a current of ~100uA from AC into your ground; that won't matter if the things are connected properly.

VLV

Decouple your DUT power from AC mains by 1:1 transformer. Then you can sense the power outputs directly; optocouplers not needed.

VLV

"TTman" kirjoitti viestissä:gyWjn.201633$ snipped-for-privacy@newsfe12.ams...

Relay with 240 Vac coil?

DING DING DING DING DING! We have a winner!! :>

Use a neon bulb coupled to some sort of photo detector. You could buy these at one time for phone ring detectors.

What do you need to detect at 240V? Simply the presence of the voltage indicating the relay has closed? Or a voltage under load to detect bad relay contacts?

Yes, I think so... thx.

Just contact closure. Post assembly testing.

Filamanet transformer?

Best regards, Spehro Pefhany

They are nice !

ch

Hi TTMan If all you want to test is whether the electromagnetic relays on a board are working correctly, any simple low current continuity detector (buzzer) will do fine. Is that all you need? amark