A capacitance meter.

(3) If the frequency of the clock pulse generator is to be 100HZ and I needed to work out the time, I will calculate it by doing this:

T = 1/F    T = 1/100   T = 0.01secs

(4) If the mark to space ratio (or duty cycle) for the astable is to be 9:1 and I had to work out:

a) The time T1, when the output voltage is high, I will use the following method.

9+1=10

0.01/10=0.001*9=0.009secs

b) The time T2, when the output voltage is low, I will use the following method.

9+1=10

0.01/10=0.001*1=0.001secs

(5) Given that C1 is to be 1μf:

a) The value of R2 will be

TL=0.693*R2*C

TL/C=R2=1443Ω

b) The value of R1 will be

Th=0.693*(R1+R2)*c

Th/0.693C=R1+R2

R1=11544

(6) The preferred value for R1 is 12kΩ and the preferred value for R2 is 1.5kΩ.

(7) The monostable multivibrator (sometimes called a one-shot mulitivibrator) is a square- or rectangular-wave generator with just one stable condition. With no input signal (quiescent condition) one amplifier conducts and the other is in cutoff. The monostable multivibrator is basically used for pulse stretching. It is used in computer logic systems and communication navigation equipment.

The operation of the monostable multivibrator is relatively simple. The input is triggered with a pulse of voltage. The output changes from one voltage level to a different voltage level. The output remains at this new voltage level for a definite period of time. Then the circuit automatically reverts to its original condition and remains that way until another trigger pulse is applied to the input. The monostable multivibrator actually takes this series of input triggers and converts them to uniform square pulses. All of the square output pulses are of the same amplitude and time duration.

(8)

Monostable multivibrator often called a one shot multivibrator is a pulse generating circuit in which the duration of this pulse is determined by the RC network connected externally to the 555 timer. In a stable or standby state, the output of the circuit is approximately zero or a logic-low level. When external trigger pulse is applied output is forced to go high (≈ VCC). The external RC network connected to the timer determines the time for which output remains high. At the end of the timing interval, the output automatically reverts back to its logic-low stable state. The output stays low until trigger pulse is again applied. Then the cycle repeats. The monostable circuit has only one stable state (output low) hence the name monostable.

(9) The maximum time the monostable output voltage is high needs to be less than the period of the astable so that themonostable has reverted to its low (stable) state before the arrival of the next trigger pulse. The maximum time is therefore 0.01s (10ms).

The values of the range resistors are 0.09, 9.09, 100, and 909.09. I worked this out by using:

Resistance=Time/1.1*capacitance.

(10) the display is to be on a meter having a full scale deflection (F.S.D) of 100μA, a resistance of 1500Ω and the saturation voltage of the transistor is 0.1v. Given Vcc is +5v, and the high output from the monostable is 4.25v, RB=100kΩ and VBE for the transistor is 0.6v, I will calculate:

1. IB using IB=Vmax-VBE/RB  

                                    IB=4.25-0.6/100000

               IB=0.0000365

2. Ic Using Ic=hFE*IB if hFE=50

                                  Ic=50*0.0000365

                                  Ic=0.001825

c) RL by using RL=Vcc-VcE/Im-Rm

                                   RL=5-0.1/0.1-1500

                                   RL=-1451

(11) A voltage regulator is used to regulate or stabilize (i.e. keep steady) the output voltage from a power-supply unit or a battery. In an unregulated power-supply the output voltage falls if the output current rises and this may upset the working of the electronic system being supplied, i.e. the load.

(12) The characteristic for a zener diode based voltage regulator is as shown.

                                  +ID

                -VD                                  +VD

                                   -ID

          +9V                                                                

                                         

                                          4V                   Rs

                   

                                                                           2.5mA

                                                                                                                              +5v

                  5V                    Iz=10mA          Voltage

                                                            Regulator

       0V                                                Output

To calculate Rs I will use OHMS law.

Rs=V/I

                                 Rs=9/0.0125

  Rs=720Ω

(13) The zener fails to regulate when the current through it drops to 0. the current through Rs will then be 2.5mA.

a)VRs=2.5mA*Rs

      VRs=2.5mA*720Ω

                              VRs=1800

b) The minimum voltage the battery can drop to and still provide 5V across the capacitance meter circuit is 5V.

c) Rs=VRS/2.5mA

                              Rs=1800/2.5

                              Rs=720

(14) This is the pin out diagram for the TO92 type regulator.

                                                                         

                                                                     

                                                                         

                                                                           

                                                                       

                                                                     

(15)

                                                                         

                                                                     

                                                                         

                                                                           

                                                                       

                                                                     

                                                                         

R=V/I

R=2/0.005

R=400Ω