This is a Sawtooth wave generator circuit using UJT transistors is easy. In the Figure 1 circuit used Q1 is UJT to connects with VR1(potentiometer), VR2 and C1. They act as a sawtooth wave generator circuit, by C1 to charge and discharge.
Then, current from the 5V power supply through VR1 and R2. This current and voltage that increase and reduce, cause Q1 to generate a signal. Which have the sawtooth wave signal or the ramp signal to the output, which frequency is determined with R, C as above.
When Q2-transistor is derived the signal input to conduct current as the sawtooth signal voltage by at pin E of Q2 will be connected into the output signal that has voltage from OV, then partially rises by slop up to +VCC of 5V is sawtooth waveform.
When C1-capacitor discharge voltage that enters to Q2 will reduce until cause Q2 stop conduct the voltage at pin E of Q2 so make signal out ofThus making output signal continuously as well. And in between at C1 discharge are pin B1 of Q1. It is a short positive pulse occurs as well. Which can be used to provide input to the device. To control the operation again.
How to build
You can put all parts in components layout on universal PCB board as Figure 2. What to check carefully for the polarity of the electrolytic capacitors and Diodes correctly. Pin of the Q1-UJT, Q2 is not an error.
The components List
Resistors ¼W +5%
VR1: Potentiometer, 100K
C1: Electrolytic 22uF
Q1:2N2646 UJT, Silicon unijunction transistor
Q2:2SC1815 or equivalent, 0.1A_50V NPN Transistor
Ramp Wave generator using 2N4891
This circuit is like the above circuit. There may be another way for you. Also, use UJT is main, 2N4891. The peak voltage output is about 5.4V if use power supply Voltage of 9V.
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