ADC, DAC, AND SENSOR INTERFACING
6. True or false. For a serial ADC, it takes a longer time to get the converted dig-
ital data out of the chip.
7. True or false. ADC0848 has 4 channels of analog input.
8. True or false. MAX1112 has 8 channels of analog input.
9. True or false. ADC0848 is a serial ADC.
10. True or false. MAX1112 is a parallel ADC.
11. Which of the following ADC sizes provides the best resolution?
(a) 8-bit (b) 10-bit (c) 12-bit (d) 16-bit (e) They are all the same.
12. In Question 11, which provides the smallest step size?
13. Calculate the step size for the following ADCs, if Vref is 5 V:
(a) 8-bit (b) 10-bit (c) 12-bit (d) 16-bit
14. With Vref = 1.28 V, find the Vin for the following outputs:
(a) D7–D0 = 11111111 (b) D7–D0 = 10011001 (c) D7–D0 = 1101100
15. In the ADC0848, what should the Vref value be if we want a step size of 5 mV?
16. With Vref = 2.56 V, find the Vin for the following outputs:
(a) D7–D0 = 11111111 (b) D7–D0 = 10011001 (c) D7–D0 = 01101100
SECTION 2: ADC PROGRAMMING IN THE AVR
17. True or false. The ATmega32 has an on-chip A/D converter.
18. True or false. A/D of the ATmega32 is an 8-bit ADC.
19. True or false. ATmega32 has 8 channels of analog input.
20. True or false. The unused analog pins of the ATmega32 can be used for I/O
pins.
21. True or false. The A/D conversion speed in the ATmega32 depends on the crys-
tal frequency.
22. True or false. Upon power-on reset, the A/D module of the ATmega32 is turned
on and ready to go.
23. True or false. The A/D module of the ATmega32 has an external pin for the
start-conversion signal.
24. True or false. The A/D module of the ATmega32 can convert only one channel
at a time.
25. True or false. The A/D module of the ATmega32 can have multiple external
Vref+ at any given time.
26. True or false. The A/D module of the ATmega32 can use the Vcc for Vref.
27. In the A/D of ATmega32, what happens to the converted analog data? How do
we know that the ADC is ready to provide us the data?
28. In the A/D of ATmega32, what happens to the old data if we start conversion
again before we pick up the last data?
29. For the A/D of ATmega32, find the step size for each of the following Vref:
(a) Vref = 1.024 V (b) Vref = 2.048 V (c) Vref = 2.56 V
30. In the ATmega32, what should the Vref value be if we want a step size of 2
mV?
31. In the ATmega32, what should the Vref value be if we want a step size of 3
mV?
488
ADC, DAC, AND SENSOR INTERFACING
32. With a step size of 1 mV, what is the analog input voltage if all outputs are 1?
33. With Vref = 1.024 V, find the Vin for the following outputs:
(a) D9–D0 = 0011111111 (b) D9–D0 = 0010011000 (c) D9–D0 = 0011010000
34. In the A/D of ATmega32, what should the Vref value be if we want a step size
of 4 mV?
35. With Vref = 2.56 V, find the Vin for the following outputs:
(a) D9–D0 = 1111111111 (b) D9–D0 = 1000000001 (c) D9–D0 = 1100110000
36. Find the first conversion times for the following cases if XTAL = 8 MHz. Are
they acceptable?
(a) Fosc/2 (b) Fosc/4 (c) Fosc/8 (d) Fosc/16 (e) Fosc/32
37. Find the first conversion times for the following cases if XTAL = 4 MHz. Are
they acceptable?
(a) Fosc/8 (b) Fosc/16 (c) Fosc/32 (d) Fosc/64
38. How do we start conversion in the ATmega32?
39. How do we recognize the end of conversion in the ATmega32?
40. Which bits of which register of the ATmega32 are used to select the A/D’s con-
version speed?
41. Which bits of which register of the ATmega32 are used to select the analog
channel to be converted?
42. Give the names of the interrupt flags for the A/D of the ATmega32. State to
which register they belong.
43. Upon power-on reset, the A/D of the ATmega32 is given (on, off).
SECTION 3: SENSOR INTERFACING AND SIGNAL CONDITIONING
44. What does it mean when a given sensor is said to have a linear output?
45. The LM34 sensor produces _______ mV for each degree of temperature.
46. What is signal conditioning?
SECTION 4: DAC INTERFACING
47. True or false. DAC0808 is the same as DAC1408.
48. Find the number of discrete voltages provided by the n-bit DAC for the follow-
ing:
(a) n = 8 (b) n = 10 (c) n = 12
49. For DAC1408, if Iref = 2 mA, show how to get the Iout of 1.99 when all inputs
are HIGH.
50. Find the Iout for the following inputs. Assume Iref = 2 mA for DAC0808.
(a) 10011001 (b) 11001100 (c) 11101110
(d) 00100010 (e) 00001001 (f) 10001000
51. To get a smaller step, we need a DAC with ______ (more, fewer) digital
inputs.
52. To get full-scale output, what should be the inputs for DAC?
489
