Description:
Two simple test circuits to check operation of quartz
crystals.
Notes:
In the first circuit, above the BC548 is wired as a colpitts
oscillator, the frequency tuned by insertion of a crystal. A
good crystal will create high frequency oscillations, the
output at the collector is rectified by the germanium OA91
diode and a deflection will appear on the meter. The more
active the crystal, the higher the output deflection which
may be adjusted with the preset.
Notes:
The next circuit uses a working crystal again used to
control the frequency of a colpitts oscillator. This time
the output from the oscillator is taken from the emitter and
is full wave rectified, the small dc bias will then directly
cause the second BC548 to light the LED.
