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Simple Crystal Tester Circuit Diagram. Most electronics project working with high frequency utilizes crystal in order to generate frequency as oscillator. It is used instead of coil. Coil can be checked with multi-meter if there is any fault, but checking of crystal completely is difficult. In order to solve this problem a simple project using few components is designed call crystal tester.

This circuit consist two NPN transistors, two diode with few passive component. The crystal under test is combining with transistor T1 which further work as oscillator. The combination of transistor T1, crystal under test and capacitors C1 and C2 is work as colpiitt oscillator. If the testing crystal is good then it works as oscillator with transistor T1. The output of oscillator is rectified and filtered by diode D1 and capacitor C2 respectively and given to base of transistor T2. The signal given to base conduct transistor which further glow the LED connected to the collector through resistor R3. If the testing crystal is faulty then LED1 does not glow.

PARTS LIST
Resistors (all ¼-watt, ± 5% Carbon unless stated otherwise)
R1 = 27 KΩ
R2 = 1 KΩ
R3 = 560 Ω
Capacitors
C1 = 0.001 µF
C2 = 100 pF
C3 = 0.001 µF
C4 = 0.004 µF
Semiconductors
D1, D2 = 1N4148
T1, T2 = BC550C
LED1 = Green
Miscellaneous
SW1 = push to on switch

Build a Flashing Light with Twilight Switch Circuit Diagram. Flashing light is very useful in order to indicate any obstruction or working in progress. The project automatic flashing light with twilight switch flash light in dark but during day it automatically turns off itself.

The circuit diagram of automatic flashing light with twilight switch is shown below where LDR is used as sensor. In the presence of light LDR offer low resistance and in dark it offers high resistance. When there is absence light, LDR offer high resistances which turn off the transistor T1. Due to this darlington pair made from transistor T2 and T3 is turn on which further glow bulb. The feedback from its output is given to the junction of resistor R2 and LDR as shown in circuit diagram. Due to feedback this circuit works as oscillator which work as flasher. Variable resistor VR1 is used to adjust the sensitivity of LDR.

 

 

PARTS LIST
Resistors (all ¼-watt, ± 5% Carbon unless stated otherwise)
R1 = 2.2 KΩ
R2, R3 = 1 KΩ
R4 = 3.3 KΩ
VR1 = 25 KΩ
Capacitors
C1 = 1 µF – 10 µF
Semiconductors
T1, T2 = BC547B
T3 = BEL187-P
Miscellaneous
LDR
B1 = 3V to 10V bulb