Tester circuit
The tester contains a minimum number of elements that even novice radio amateurs will definitely find in their household. The entire circuit is essentially one multivibrator assembled using transistors. It generates rectangular pulses. The controlled circuit is connected to the arms of the multivibrator in series with two LEDs, counter-parallel. As a result, the circuit under test is tested with alternating current.
Operating principle of the tester for checking radio components
An alternating current is removed from the working multivibrator, approximately equal in amplitude to the power source. Initially LEDs do not light up because the circuit is open. But if you close the probes, then alternating current will flow through LEDs. At this time through LEDs an alternating current with a frequency of approximately 300 Hz will flow. As a result of back-to-back connection LEDs will flash alternately, but due to the high generation frequency this will not be visible to the human eye, but it will be seen that both LEDs are simply glowing at the same time.
What does this give? - You ask. For example, if you connect a diode to the probes, only one LED will light up, since the alternating current will flow only after one period. As a result, it will immediately be clear that the connected diode is working. The same thing is observed when checking transistor transitions.
The main convenience of this tester is that you can immediately see whether the diode junction is working or not. There is no need to turn the elements over to match the polarity of the tester, as in a conventional multimeter. This gives a huge advantage when testing a large number of radio elements, and is generally very convenient.
You can also check other elements or circuits for breakdown or breakage.
The tester can be assembled on a board or mounted. It is better to take LEDs of different colors so that the work can be clearly seen visually.
Also, using this simple device, you can quickly determine where the cathode and anode of an unknown diode are. But to do this, you need to mark the location on the tester LEDs.
For power, I used a 3.7 V lithium-ion battery. But you can take 2-3 1.5 V “pinky” batteries connected in series.
In general, this is a very necessary thing. I recommend that you repeat this simple device. And you are guaranteed ease of use, since in most cases you need to determine the serviceability of the radio element, and not its parameters.
