WARBLE TONE GENERATOR
In the schematic shown in figure, the first 555 oscillates below 10 Hz. Its rectangular output is filtered by filter R3, R4 and C3 to produce triangular waves which modulate the 1 kHz oscillator using the, second 555 in astable mode. The exact frequency, rate and deviation of the circuit can be easily modified to produce almost any type of warble sound. The output may be amplified by an audio amplifier to the required power level.
LINEAR SAW TOOTH GENERATOR
The voltage across the timing capacitor CT in the monostable multivibrator circuit, rises to 2/3VCC and then drops to almost zero. A sawtooth waveform is, therefore, available across this capacitor, but is not linear because the capacitor voltage rises exponentially. In figure shown above, the capacitor is allowed to charge via a constant current source comprising of T1, RI, R2, R3 and R4. The voltage now rises linearly and the output is taken via an emitter follower buffer stage T2 to isolate the load from the timing circuit. For use as a scope time base, a trigger signal may be applied to terminal 2 of the IC.
Another arrangement by which a linear sawtooth can be produced is by bootstrapping the output as shown in figure, Capacitor C1 begins to charge through R1, R2, and R3 towards VCC. The voltage across R5 at the output of emitter follower T1 is almost same as that at pin 7 of the IC. This voltage is fed back to junction of R1 and R2. As a result, the voltage across R2 remains essentially constant during C1's charging cycle and the capacitor voltage rises linearly. Connecting pin 2 to pin 6 causes the circuit to trigger itself and free run as an astable multivibrator.
Alternatively, the synchronizing signal may be applied to pin 2.
Resistor R3 is required to slow down the negative discharge slope of the saw tooth. R3.C1 is kept greater than 5 micro-seconds.
Resistor R3 is required to slow down the negative discharge slope of the saw tooth. R3.C1 is kept greater than 5 micro-seconds.
SQUARE WAVE GENERATOR
With only one external resistor and one capacitor and a 555 timer IC, can be made to generate fairly accurate square waves.
The square wave generator circuit shown in figure makes use of the fact that output voltage in a 555 IC is 1800 out of phase with the capacitor voltage. To understand the circuit operation let us assume a state when output is high and the capacitor C1 is charging via R1. When the voltage across capacitor reaches 2/3VCC, the output goes low and C1 now starts discharging through R1. When the voltage across C1 falls to 1/3VCC, the circuit trips again, output goes high, the capacitor starts charging and the cycle repeats endlessly. Since charging and discharging takes through R1 only, the output is a symmetrical square wave. The period of oscillator is given by T= 1.4RC, F=1/T.
The square wave generator circuit shown in figure makes use of the fact that output voltage in a 555 IC is 1800 out of phase with the capacitor voltage. To understand the circuit operation let us assume a state when output is high and the capacitor C1 is charging via R1. When the voltage across capacitor reaches 2/3VCC, the output goes low and C1 now starts discharging through R1. When the voltage across C1 falls to 1/3VCC, the circuit trips again, output goes high, the capacitor starts charging and the cycle repeats endlessly. Since charging and discharging takes through R1 only, the output is a symmetrical square wave. The period of oscillator is given by T= 1.4RC, F=1/T.
The output symmetry depends on the accuracy of the timer's internal resistor string which produces the IC's comparator reference voltages. These errors can be eliminated by adding a trimming resistor R2 and connecting it to supply line or ground depending on the correction needed.
SENSE OF TIME TESTER
How accurate is your sense of time? You can find it out for yourself by catching a flashing LED.
When S2 is on, the circuit in Figure, operates as an astable multivibrator and the LED is lit for about 0.1 sec flashing every 1.5 seconds. Since the human reaction time is more then this, you cannot catch it once it is seen on, by pressing S1. If your sense of time interval is good. and you press S1 within that 0.1 Sec, the discharging of C1 stops and the lamp stays lit. You may change the ON and OFF periods by changing R1 and R2 or C1 to suit your convenience.
When S2 is on, the circuit in Figure, operates as an astable multivibrator and the LED is lit for about 0.1 sec flashing every 1.5 seconds. Since the human reaction time is more then this, you cannot catch it once it is seen on, by pressing S1. If your sense of time interval is good. and you press S1 within that 0.1 Sec, the discharging of C1 stops and the lamp stays lit. You may change the ON and OFF periods by changing R1 and R2 or C1 to suit your convenience.
SOLID STATE FLASHER
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