1. Explain what is 555 timer?

The 555 times is a highly stable IC that can produce accurate and highly stable time delays or oscillation. The frqeuency of oscillation and duty cycle are accurately controlled by only two external resistors and a capacitor.

2. Explain what do you mean by a grounded load?

When the load is connected between the output terminal (pin 3) and grounded terminal (pin 1), it is called grounded load, this is also sometimes called the normally off load.

3. Explain why normally control terminal of 555 timer is connected to ground through a 0.01µF bypass capacitor?

Normally control terminal (pin 5) of timer is connected to ground through a 0.01µF bypass capacitor so as to prevent noise coupled onto this pin from causing false triggering.

4. Explain what are the two basic modes in which the 555 timer operates?

The 555 timer basically operates in one of the two modes – either as monostable or as an astable multivibrator.

5. Name the CMOS version of the 555 timer.

IC 7555.

6. The function of Pin 3 is:

A. Control Voltage
B. Discharge
C. Output
D. Reset
E. Threshold
F. Trigger

Ans: C

7. The function of Pin 6 is:

A. Control Voltage
B. Discharge
C. Output
D. Reset
E. Threshold
F. Trigger

Ans: E

8. The function of Pin 5 is:

A. Control Voltage
B. Discharge
C. Output
D. Reset
E. Threshold
F. Trigger

Ans: A

9. The function of Pin 4 is:

A. Control Voltage
B. Discharge
C. Output
D. Reset
E. Threshold
F. Trigger

Ans: D

10. What is the function of the Threshold pin?

A. To charge the capacitor “C”
B. To discharge the capacitor “C”
C. To detect when the capacitor is “HIGH”
D. To detect when the capacitor is “LOW”

Ans: C

11. What is the function of the Discharge pin?

A. To charge the capacitor “C”
B. To discharge capacitor “C”
C. To detect when the capacitor is “HIGH”
D. To detect when the capacitor is “LOW”

Ans: B

12. What is the function of the Trigger pin?

A. To charge the capacitor “C”
B. To discharge the capacitor “C”
C. To detect when the capacitor is “HIGH”
D. To detect when the capacitor is “LOW”

Ans: D

13. What is the function of the Reset pin?

A. To discharge the capacitor “C”
B. To reset the chip
C. To make the output of the chip “HIGH”

Ans: B

14. The Discharge and Output are:

A. In phase with each other
B. Out of phase with each other

Ans: A

15. What does pin 6 do?

A. Charges the capacitor “C”
B. Discharges the capacitor “C”
C. Detects the HIGH on capacitor “C”
D. Detects the LOW on capacitor “C”

Ans: C

16. When pin 2 detects the voltage-level on the capacitor does the capacitor begin to charge or discharge?

A. Charge
B. Discharge

Ans: A

17. What does pin 2 do?

A. Charges the capacitor “C”
B. Discharges the capacitor “C”
C. Detects the HIGH on capacitor “C”
D. Detects the LOW on capacitor “C”

Ans: C

18. In the following diagram, is the output predominantly HIGH or LOW? Remember: Pin 7 and 3 act “in harmony”

A. HIGH
B. LOW

Ans: A

19. To increase the output frequency of a 555:

A. Increase the value of capacitor “C”
B. Decrease the value of capacitor “C”

Ans: B

20. If the resistors in Q13 are swapped, does the output frequency change?

A. It increases
B. It decreases
C. Little or no effect

Ans: B

21. What does pin 7 do?

A. Charges the capacitor “C”
B. Discharges the capacitor “C”
C. Detects the HIGH on capacitor “C”
D. Detects the LOW on capacitor “C”

Ans: B

22. If the value of R1 is increased:

R1 : 100k, R2:1K

A. The output frequency increases
B. The output frequency decreases
C. The overall frequency does not alter

Ans: B

23. Name the resistor(s) that effect the timing of the “LOW OUTPUT”:

A. R1 and R2
B. R1 only
C. R2 only

Ans: C

24. For a 5v circuit, if pin 4 is taken to 1v, does the chip reset?

A. Yes
B. No
C. Cannot be determined

Ans:B

25. When pin 2 detects the voltage-level on the capacitor, what happens to the output?

A. It goes HIGH
B. It goes LOW

Ans:A

26. For the following diagram, which resistor(s) controls the “SPACE:”

R1 : 100k, R2 : 1k

A. R1
B. R2
C. R1 + R2

Ans:B

27. The maximum frequency of operation for a 555 is:

A. 100kHz
B. 500kHz
C. 5MHz
D. 500Hz

Ans:B

28. For the following diagram, the Mark:Space ratio will be:

R1: 100k, R2: 1k

A. Greater than 50%
B. Less than 50%
C. Equal
D. Unable to be determined

Ans:A