How it works.
Beginning, we look at work before, in Figure below.
-The transistor Q1 (BC107) is the key to the oscillated circuit. By will create frequency, when the crystal put on the socket to the base pin (B) of Q1.
-When the switch S1 is pressed to the circuit, the current from the battery (B1-9 volt) to flow into the circuit, the oscillated signal from emitter pin (E) of Q1 pass through to C4.
The oscillator signal will be changing all the time, need to smooth with D1 and D2. Then, the signal is passed to the C5, which helps smooth up. At C5 has voltage across it, is a positive voltage to trigger a bias current to the Q2 works, as a result, the LED1 lights.
The R3 limits the current through the LED1 to a value not exceeding 20 mA. If more than this, LED lights too and short-lived to LED1.
The above principle sees that LED1 is illuminated when the transistor Q1 works. The Q1 will work, and build frequency, it requires that the crystal quality. to use this principle, we can easily measure the crystal.
How to build Crystal tester circuit
This project use equipment less. Therefore can be soldered onto the perforated board, easy to save money and time.
When creating a Crystal tester circuit is complete, it’s the test circuit. First, find a good crystal to test in the circuit. Then press S1 to see the LED1 brightness. But if it is shut down showing that the circuit may be wrong. You may have forgotten the battery or alternating polarity LED1 or other.
The parts of circuit
Q1, Q2: BC107, NPN transistor
D1,D2: DRL=1N4148 75V 150mA Diodes
R1: 27K 0.25W Resistor
R2: 1K, 0.25W Resistor
R3: 560 ohms, 0.25W Resistor
C1: 0.1uF 50V Polyester Capacitor
C2,C4: 330pF 50V Polyester Capacitor
C5: 0.0047uF 63V Polyester Capacitor
LED1: any color as you like.
Finally, we have the electronics tool next one on our desk. it can be used to check the crystal used in radio transmitters, radio control, the digital computer clock circuit and so on.
This circuit does not have PCB layout. Thus, you can see the crystal tester circuit below with PCB layout. Which is a similar structure of the circuit? but the detail of components slightly different. The hope is to build this project even easier.
Crystal tester circuit with PCB
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