Build Your Circuit Board Integrity Test – 22K Schematic

Description

This compact circuit demonstrates the fundamental assessment of a printed circuit board, identifying 0V, a power supply voltage ranging from less than 3V to 30V, and any detached segments. When the probe is isolated, as it would be in a damaged track, both LEDs exhibit a faint glow, as there’s no current flowing through the transistors. Conversely, if the probe makes contact with 0V or a positive voltage, one or the other LED illuminates brightly. A digital signal should trigger their illumination in direct proportion to the mark-space ratio, while the output of a circuit oscillating at a frequency below approximately 20Hz will cause the LEDs to flicker intermittently. The LEDs are continuously lit at a stable brightness level, irrespective of the voltage supplied, due to their operation via a straightforward FET constant-current source (Q1).

Circuit diagram:

Parts:

More about components

BF245

The BF245 is a versatile NPN bipolar junction transistor commonly used as a general-purpose transistor in various low-power applications. It is characterized by its relatively high current gain, allowing it to amplify small currents into larger currents. It’s often utilized in switching circuits and amplifier designs due to its robust performance and ease of use. This transistor plays a vital role in the circuit’s functionality, acting as a current-source, providing a constant current to the LEDs.

Notes: