Test Probe Finger Trigger

Hi,

This little project was created for our electronics testing department to make daily tasks a bit easier.

We use custom-built test equipment and workflows based on the following setup:

• Voltage/current measurement devices with GPIB interface
• 4 mm measurement cables
• PC running custom test software
• A workflow for measuring voltages and currents at specific test points

The test software (a custom .NET program for Windows) initiates each measurement and progresses using the “Enter” key. This setup requires both hands—one to hold the test probe, the other to press the keyboard. In the past, we’ve had a few accidents with slipped probes (cue the magic smoke 😬).

This design helps reduce the risk of slipped probes and improves overall user comfort. Each push of the switch sends an “Enter” keystroke to the connected PC via USB. The button is debounced in software, and no special USB driver is needed—the Digispark handles everything. I tested this successfully on four different PCs.
 

Print Settings:

• Layer height: 0.16 mm (0.4 mm nozzle)
• Perimeters: 3
• Infill: 10% gyroid
• Solid layers: 3 top, 3 bottom
• Supports: Yes, organic
• Print orientation: As shown in the image
• Total print: ~8g, approx. 50 min

BOM & Source Code: Provided below. Feel free to modify the code—sending different keys or even full strings is possible.

Notes:

I recommend keeping the cable between the test probe and the controller under 1 meter. During development (without the cable), everything worked fine. But after adding the cable in the final prototype, we noticed occasional skipped inputs. It’s likely a signal integrity issue related to cable length.

If you run into problems, try shortening the probe-controller cable and extending the USB cable to your PC instead. Also consider adjusting the wait value, or removing line 88 altogether (marked with “<<<< experiment with this value”).

The sketch only uses around 21% of the program memory—plenty of room for future tweaks.

The firmware was written with the Arduino IDE. For the nessecary board manager and board selection in the IDE see the remarks at the start of the code.

Happy printing!