To get a nice, clear audio output from the CLUE, we'll add an amplifier/speaker breakout board. The STEMMA Speaker board plus JST-to-alligator clips cable makes it easy.

Hook Up

Plug the JST 3-pin cable into the STEMMA Speaker board. It is keyed to only go in one way.

Now, connect the three alligator clips to the CLUE board from the back side. Make these connections:

  • white to pin #0
  • red to pin 3V
  • black to pin GND

If you are sending audio TTY transmissions over a phone line to a TTY machine on the other end of the line, you'll simply hold the STEMMA speaker to the mouthpiece of your phone handset.

To test on a local machine (and see the text show up on the supremely awesome vacuum fluorescent display!) you can hold the speaker to the mic input coupler, or more permanently attach it with rubber bands as shown below.

Wrap two rubber bands around the mouthpiece coupler on the TTY machine.

Place the STEMMA speaker directly over the coupler stalk.

Criss cross the rubber bands over the STEMMA speaker board to hold it snugly in place (the fewer unwanted mechanical vibrations the better).

You may also use a single rubber band to hold the CLUE board onto the battery cover as shown.


Most TTY machines can be powered from batteries or a DC 9V wall adapter.

You can choose to power your CLUE from USB power or a battery, such as a LiPo or a small 3x AAA battery pack.

This guide was first published on May 05, 2020. It was last updated on May 05, 2020.

This page (Assemble the Transmitter) was last updated on Apr 29, 2020.

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