Monitoring status light with cds photocell

[michelkenny]

I'm trying to monitor the status of my washer and dryer with a cds photocell. I've connected them to an analog input on the Elk M1. When the status light is off, the zone reads around 13.6 V. When the status light is on, the zone reads around 12.6 V to 13.0 V. Is there a way that I can make the voltage difference larger? I'm hoping that I can use a regular contact zone definition, and have the non-secure and secure statuses without having to look at voltages.

 

[apostolakisl]

I'm trying to monitor the status of my washer and dryer with a cds photocell. I've connected them to an analog input on the Elk M1. When the status light is off, the zone reads around 13.6 V. When the status light is on, the zone reads around 12.6 V to 13.0 V. Is there a way that I can make the voltage difference larger? I'm hoping that I can use a regular contact zone definition, and have the non-secure and secure statuses without having to look at voltages.

You might consider a photo-transistor like this. http://www.ebay.com/itm/20x-Rohm-3mm-Photo-Detector-Phototransistor-/220780676176?pt=LH_DefaultDomain_2&hash=item33678dc450 The hard part here would be keeping the ambient room light off of it since these don't usually require much light to have the resistance go to zero. You should be able to use an Elk zone as short/open with something like this. You might consider an opto-isolator as well, you would need to open up your washer and wire it in parallel with the led light on the washer itself. An opto-isolator would work for sure, it is just the part about having to open up the washer control panel that makes it hard.

 

[JimS]

It sounds like you might be able to adjust the resistor in series with the photocell to get a better range of voltages. Is the devices shielded from room light? I am guessing (and please correct me if I am wrong) that the CDS cell is from ground to the input and then you have a pull up resistor to some positive voltage. If thats true try using a larger value resistor. I would think the analog input would be a fairly high impedance and not load the circuit much.

Here's a couple related items if you haven't seen them...

http://www.cocoontech.com/portal/articles/tutorials/home-automation/29-how-to-monitor-the-status-of-a-device-using-its-status-light

http://www.cocoontech.com/portal/articles/tutorials/home-automation/412-how-to-remotely-monitor-an-appliances-status-light

 

[BraveSirRobbin]

http://www.cocoontech.com/portal/articles/tutorials/home-automation/29-how-to-monitor-the-status-of-a-device-using-its-status-light