E-Textile Logic Probe – Debugging Tool

Introduction:

Logic probes are useful debugging tools that are used to analyze logical states (0 and 1) in a circuit, they are also cheap and easy to build. I took this concept and made a logic probe for e-textile makers, specifically beginner students, to easily test and debug their code and circuitry without needing to break out a multimeter.

The logic probe has two states – red and blue:

Red indicates a high logic state, meaning that the probe is in contact with a thread that is set to high (>2.5 volts).

Blue indicates a low logic state, meaning that the probe is in contact with a thread that is below .7 volts or is grounded.

The output from the logic probe can be broken down as such:

Output | Meaning

Red LED is on | Logic output is HIGH

Blue LED is on | Logic output is LOW

Both LEDs are on | The logic output is switching between HIGH and LOW

No LEDs are on | The probe is not connected to a thread, and/or the probe is not connected to the microcontroller GND or VCC.

The logic probe works with supply voltages up to 12V and can be used to detect TTL and CMOS as well.