Using a Relay to trigger a SmartThings alert

Our dryer has an annoying buzzer that frightens anyone who isn’t used to its piercing report. One of the first things I did when we moved in was to disconnect it. But there was a downside. The sound was a not so gentle reminder that the load was dry. Using some of the electronics knowledge I’ve gained from my amateur radio hobby, I was able to construct a system to send an alert to my iPhone when the laundry was done.

The buzzer was fired by a 2 second 120VAC pulse, perfect to energize the coil of a relay. I found the URBEST HH52P DYF08A unit on Amazon for under $10.00.

The AC voltages creates a magnetic field which pulls changes the state of the relay contacts. Since it’s a double pole / double throw device, I had the option of solving for an open or a closed circuit.

Enter the Ecolink Door & Window Sensor, White & Brown (DWZWAVE2.5-ECO). Normally the included rare earth magnet is used with the device to tell you when someone opens a door or a window. But inside the case are two green screw terminals which respond to a change in state, sending an alert to my Samsung SmartThings Hub.

I wired the 120VAC connection from the dryer to the relay coil and connected the screw terminals on the sensor to the Normally Closed connections on the relay. Now when the dryer shuts off, instead of a loud buzz, I get a pop-up alert on my smart devices. The sensors are easily programmable within the SmartThings ecosystem, via either a web browser or their apps for iOS and Android. You can send whatever custom message you wish.

I use the sensors for their intended application on the front door of our place, part of my smart home setup that controls lighting and my repeater power strip. As control operator, I wanted to have as many backup cut-off systems as possible.

Interestingly, the connection schematic was printed in very small graphics on the to the relay. Here’s an easier to see graphic, should you decide to experiment with your own applications using the device.

The red dot on the relay, shown above is oriented to the bottom (coil side) of the schematic.