The tester can not only detect rectangular wave signals, it can also generate them. The test signals may be generated continuously or for a preset period as required.
The detector part is based on IC2. A signal input to K3 is applied to IC2. where it is divided by 1024 and then fed to a buzzer. The buzzer will sound at a frequency
between 1 Hz and 10 kHz if a signal is present at a frequency between 1 kHz and 10 MHz respectively.
The generator is formed by monostable 1C 1a and variable oscillator IC1b. The pulse width of the monostable may be set width P1 to ls maximum. The monostable is started when push-button switch S1 is pressed. Rotary switch S2 serves to select a continuous or a burst signal: in its third position, there is no output. The oscillator operates over three ranges selected by S3: 1 Hz, 100 Hz, 10 kHz. The wanted frequency is selected with P2. The required signal is available at K2.
Although the tester may be powered by a 9-V battery, provision has been made for an external 5-15 V source. Diode DI serves as Power on indicator. Switch S4 is the on-off switch. The tester draws a current of about 50 mA