Quote:
Originally Posted by Jeg
Hi Jh
Your voltage levels at sensor's output look that they are normal.
Assuming that your circuit is correct, then try the following.
When your voltmeter is connected alter your potentiometer to adjust again the buzzer/led threshold. Normally you will be able again to turn on your led.
Find a way to firm your meter's probes on the right points and then move your hands away to see if there is a variation on numbers. Then attach antenna with your hand and confirm that the output voltage drops down.
In general, device interacts with your body as it uses it to close the circuit between device and earth. Your hand acts as a capacitor plate. When you adjust your device your hand has to be firm and steady attaching the handle of your device or your aluminum box.
Regards
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I state that the calibration inside the laboratory is difficult due to the many disturbances and the calibration must be done with the antenna inserted. Once the right value at the sensor stage output has been established, it connects to the display stage and any measurements, if the LEDs do not light up by varying the threshold, then the controls must be done on the display stage. If you want to measure the output on the collector of TR4 with the oscilloscope, the signal at the sensor stage output goes to zero.