TINY COMM TESTER: For Clear-Com compatible intercom systems.
by Scott Helmke
Similar to the Tiny Phantom Power Tester, this is another very simple idea that’s an important part of my toolbox. This allows very quick testing of an analog, Clear-Com style intercom line to make sure it’s receiving power, signal, and can help find stations and belt packs that are causing problems for the whole intercom circuit. I was actually hoping to design a slightly more complicated tester that would do a few different things, but ran into serious feature creep compared to the utility of this little wonder.
How to build
The theory is pretty simple. Clear-Com analog party-line intercom puts the 30 volts DC power for all the belt packs and remote stations between pins 1 and 2 of an XLR connector, and the audio signal between pins 1 and 3. The “Call” function works by adding 12 volts DC to the audio signal.
So this tester simple uses a green LED to show the presence of the power, and a red LED to show the presence of the call light voltage. Resistors have been added to each LED to limit the amount of current and keep the LED from burning out.
Construction is fairly easy – you just need an XLR connector, usually the sockets (“female”) end, one green and one red LED, and two resistors. I built mine with a 2.2k ohm resistor for the green LED (power), and 1k ohm resistor for the red LED (audio and call light). The resistor values don’t have to be exactly what I used, either.
Make sure that you connect the red LED between Pin 3 and Pin 1, and the green LED between Pin 2 and Pin 1. To finish, I added heat shrink over all the components.
How to use
Using the tester is fairly simple, just plug it into an intercom circuit to see if power is present – that’s the green LED lighting up. If you press the Call button on a belt pack the red LED should light up. If both of those tests work then the intercom should be working.
Sometimes a belt pack or remote station will go bad, causing all the call lights on the line to light up and kill the audio signal. I’ve used these testers to quickly find the bad unit, by disconnecting belt packs and stations until the red LED goes dark. Very useful if you’re by yourself checking remote intercom drops in spot booths.
For more technical tips, sign-up for our email newsletter!
