Expt 5

Frequency to Voltage Conversion Circuit EXPT: 5 Objective: This experiment is intended to study frequency to voltage conversion circuit and to measure the frequency of an unknown signal. Theory: When the 555 timer is operated as a mono-stable (one-shot) mode the output voltage is low until a negative going trigger pulse is applied to the input. The output switches to high as soon as it is triggered by negative pulse. The period of time, the output is high , is determined by the RC network externally connected to the IC. At the end of the rimming interval, the output whose width is given by, t=1.1RC seconds. If the mono-stable timer is triggered by a train of negative pulses, obtained from asignal of frequency f, the average dc output of the timer will be: Vout =Vcc tf=1.1Vcc fRC (1) Now the voltage output is first measured for a standard frequency fs So that: V1 =1.1 Vcc fs RC (2) Then the voltage output is measured for unknown frequency fx again when : V2 =1.1Vcc fx R (3) From the equations (2) and (3) the unknown frequency determined by: Fx=fs (V1/V2) (4)

Apparatus: 1. Timer 555 2. Transistor C828 3. Opamp 741 4. Resistor (1K-2Pc., 4.7 K-Pc., 10K-2Pc.) 5. Capacitors (0.01 uf-2Pc., 0.1 uf –1Pc.) 6. Trainer board 7. Wires and leads 8. Voltmeter 9. Oscilloscope 10. Function Generator

Circuit Diagram:

Data: Cs

V1

V2

Cx

Questions: 1. Show wave shapes at different points. 2. Measure the unknown frequency using five different standard frequencies. 3. Take the average and compare the value with the reading of the source display.