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# Circuit Board Checker(BF245)

2017-08-04 00:48
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This article describes the Circuit Board Checker (BF245). The principle is very simple, very practical. The circuit components can help you understand better grasp this principle. For example, in this circuit, you can go to find and buy these components: BF245.

Indicates the basic integrity of a printed board, Self-powered – 3 to 30V range

This little circuit indicates the basic integrity of a printed board, detecting 0V, positive supply voltage from less than 3V to 30V and floating parts. If the probe is floating, as it would be in a broken track, then bothLEDs barely light up, since there is no current to drive the transistors, but if the probe touches 0V or a positive voltage one or other lights. A digital signal should light them in proportion to the mark-space ratio whereas the output of a circuit oscillating at a frequency rate below about 20Hz will cause theLEDs to flicker alternatively. TheLEDs will illuminate always at a constant intensity, no matter the voltage supply used, because they are fed by a very simpleFETconstant-current generator (Q1).

Circuit Diagram

#### Figure 1 Circuit Board Checker Circuit Diagram

Parts:
R1 = 22K
R2 = 22K
D1 = RedLED
D2 = GreenLED
Q1 = BF245
Q2 = BC547
Q3 = BC557

Notes:

The Black clip must be connected to the negative ground of the board under test.The Red clip should be connected to a positive voltage source (not exceeding 30V) available on the same board.Metal probe is suitable for this circuit.Two Miniature Crocodile Clips (Red and Black) are also necessary.