1. B. H. GARDI COLLEGE OF ENGG. & TECH. ANALOG ELECTRONICS
DIGITAL CONTROLLED DC MOTOR
GUIDED BY: PREPARED BY:
PROF. SHVETAL PANDYA PARTH VAGHELA
PROF. JAYDEV JADEJA (13EE042)
PROF. RAKESH OZA DHAVAL JOSHI
(13EE024)

2. we need two Ics to make this type of circuit , which is,
555 timer IC
MOSFET

3. 555 TIMER IC
One of the most versatile linear integrated circuits is 555 timer. Signetics corporation first introduced this device as SE/NE 555 in early A sample of these applications includes monostable and astable multivibrator.

4. PIN DIAGRAM OF 555 TIMER

5. ASTABLE OPERATION
555 timer as astable multivibrator

6. OPERATION :
As shown in figure 555 timer connected as astable multivibrator.
Initially when the output is high,capacitor C starts charging towards Vcc through Ra and Rb .
However as soon as voltage across the capacitor equals 2/3 Vcc, comparator 1 triggers the flip-flop,and output switches low.

7. Now capacitor C starts discharging through Rb and transistor Q1.
When voltage across C equals 1/3 Vcc,comparator 2’s triggers the flip-flop,and the output goes high. Then cycle repeats.

8. The output voltage and capacitor voltage waveforms are shown in figure ,

9. As shown in this figure, the capacitor is periodically charged and discharged between 2/3 Vcc and 1/3 Vcc,respectively.
The time during which capacitor charges from 1/3 Vcc to 2/3 Vcc is equal to the time the output is high and is given by
Tc=0.69(Ra+Rb) ……(1)

10. Where Ra and Rb are in ohms and C is in farads
Where Ra and Rb are in ohms and C is in farads. Similarly,the time during which the capacitor dischrged from 2/3 Vcc and 1/3 Vcc is eqal to the time the output is low and is given by
Td=0.69(Rb)C ……(2)
Where Rb is in ohms and C in farads. Thus total period of the output waveform is
T=Tc +Td =0.69(Ra+2Rb)C ……(3)

13. The duty cycle of square wave is 50%
The duty cycle of square wave is 50%. This means that,acording to eqation (5) the astable multivibrator will not produce sqare-wave output unless the resistance Ra=0Ω.
However, there is a danger in shorting resistance Ra to zero. With Ra=0Ω, terminal 7 is connected directly to +Vcc.

14. When the capacitor discharges through Rb and Q1 (pin 7),an extra current is supplied to Q1 by Vcc through ashort between terminal 7 and +Vcc,which may damage Q1 and hence the timer.

15. ASTABLE MULTIVIBRATOR

16. ASTABLE MULTIVIBRATOR OUTPUT

17. MOSFET
In this circuit it works as motor driver. We connect it’s three terminal as below, Output of astable multivibrator connected to GATE terminal of MOSFET. Also one resistor of 1kΩ is connected between GATE terminal and ground.

18. SOURCE terminal of MOSFET is connected to ground
SOURCE terminal of MOSFET is connected to ground. Motor is conected between DRAIN terminal of MOSFET and 12V supply.

19. Digital Controlled DC Motor

20. We have connected Rb as 1M potentiometer ,so by changing value of resistor we can control the speed of motor . We can also use potentiometer in place of Ra. So by changing value of potentiometer we can control the dc motoer.

21. Thank you