Self Test on Tutorial 8
1. A 555-timer is used as a monostable and this is the circuit.
(a) Put a ring around the RC network system.
(b) Which pins are used for the positive supply voltage and the negative (0 V)?
(i) Supply Voltage
(c) The LED has a voltage of 2.2 V across it when it is fully lit, and takes a forward current of 10 mA. Calculate the voltage across the 1 k resistor. Hence work out the voltage at pin 3.
(d) Draw the output of the monostable when switch S is pressed.
(e) State and explain what, if anything, would be the effect of pressing the switch S again, if the output is still high
(f) If R = 2.2 k and C = 1.5 mF, what is the time period of the monostable pulse?
2. A 555-timer is shown in astable mode.
(a) Identify a potential divider on the circuit by drawing a ring around it. Show it clearly.
(b) If R1 = 10 k, R2 = 6.8 k, and C = 150 nF, calculate the RC time constant before it is connected to the 555-timer
(c) The output of the circuit is said to have mark time and space time. Explain what these two terms mean.
The circuit is constructed so that R1 = 10 k, R2 = 6.8 k, and C = 150 nF
(d) Calculate the mark time.
(e) Calculate the space time.
(f) Calculate the mark to space ratio.
(g) Draw the output you would see on a CRO screen