Quartz crystal selection tester

Quartz crystal selection tester
Make a quartz crystal selection tester yourself, use light-emitting diodes to display the test results, which is fast and accurate. As shown in the figure.
Insert the quartz crystal tube BX to be tested into the sockets XS1 and XS2, press the button SB, if BX is good, the oscillator composed of transistor VT1, capacitor C1, C2 and other components will work, the oscillation signal is emitted from VT1, coupled to VD2 for detection through C3, filtered by C4, and becomes a retained signal voltage, which is sent to the base of VT2, so that the transistor VT2 obtains a forward bias voltage and turns on, so the light-emitting diode LED emits red light, indicating that the quartz crystal under test is good. If the LED is not on, it means that the quartz crystal is bad.
Selection of production components: R1~R3yong RJ-0.5 metal oxide film resistors, C1~C3 use mica capacitors, and C4 uses CJ11 capacitors. The β values ​​of VT1 and VT2 are 50~100, and their fr≥3000MHz.
By appropriately changing the capacitance of C1 and C2 (variable capacitors can be used instead), it can be used to test quartz crystals of different frequencies.