Crystal „XTAL“ tester

Miniature crystal tester with the possibility of measuring frequency.

The following crystal tester allows fast testing of crystals from a frequency of about 0.5MHz. In addition to the connector, it is all designed for SMD mounting and allows the connection of a counter to measure the frequency.

Circuit diagram:

The following figure shows the wiring diagram.

xtal tester circuit
img. 1: Circuit diagram

The tester circuit consists of two separate parts. The first, formed by transistor T1, is a crystal oscillator. The crystal is of course connected externally to pins J3 and J4. When a functional crystal is connected, the transistor oscillator oscillates. After passing through capacitor C3, this frequency is rectified on diodes D1 and D2 and filtered by capacitor C4. The voltage rectified in this way is subsequently amplified by transistor T2, which lights up the LED D3.

If necessary, it is possible, preferably again, to connect a counter to the emitter of transistor T1 via a small capacitor and read the frequency on it.


The crystal tester was designed for SMD design.


xtal tester pcb
Img. 2: Placement plan (TOP)

crystal tester board
Img. 3: Placement plan (BOTTOM)
crystal tester pcb
Img. 4: Printed circuit board (600 dpi original size)

The connection was, of course, set up and its correct function verified.

xtal tester module
Img. 5: Assembled module
crystal tester module
Img. 6: Assembled module – bottom side
R1             33k 0805
R2             1k 0805
R3             470R 0805
C1             1n 0805
C2             100p 0805
C3             1n 0805
C4             10n 0805
D1             BAT48 SMD
D2             BAT48 SMD
D3             LED 3mm red
T1             BC817
T2             BC817

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