[STE] Easy Transistor Tester circuit using CMOS CD4093 

Easy Transistor Tester
The circuit employs the properties of the gates of low power IC 4093. It is a NAND IC with four gates that can be designed in various ways. Here the first gate (N1) is designed as a simple oscillator with resistor R1 and capacitor C2. The remaining gates are used as inverters and buffers. The output of gate N1 (pin 3) is fed to gate N2 (pin 4), which, in turn, is used to drive the green half of bicolour LED1 (I modified it again by two Leds).
Circuit operation
If the TUT inserted in the socket is npn type, the current flows from output pin 4 of gate N4 through bicolour LED1 and its green half glows. This is due to conduction of the TUT. If the transistor is pnp type, the current flow is reversed and the red half of bicolour LED1 glows. This happens due to the high state of outputs at pins 10 and 11 of gates N3 and N4, respectively. This is because output pin 4 of N2 is at low level.
Bicolour LED1 used in the circuit is a two-lead version with red and green LEDs connected in inverse parallel inside a common case. The cathode of one LED forms the anode of the other, so depending on the direction of current flow either red or green LED lights up.
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This project is quoted from the document "270 MINI ELECTRONICS PROJECT WITH CIRCUIT DIAGRAM", written by Suman Debnath.
- Project 198
- Page 118