Analog-to-Digital Converter - The HCS12/9S12: An Introduction to Software and Hardware Interfacing - page 630

E12.14 The LM35 from National Semiconductor is a Centigrade temperature sensor with three
external connection pins. The pin assignment and circuit connection for converting tempera-
ture are shown in Figure E12.14. Use this device to construct a circuit to display the room tem-
perature in Celsius. The temperature range to be converted is from 227 o C to 100 o C. Describe
the circuit connection for a digital thermometer made up of the HCS12 and the LM35, and
write a program to display temperature on the LCD.

V S
(+4 V to +20 V)

+

V S

V OUT

Choose R 1 = V S /50 μ A
V OUT = +1500 mV at +150°C
= +250 mV at +25°C
= -550 mV at -55°C

LM35

LM35

V OUT =
+10.0 mV/°C

R 1

- V S

(a) Circuit connection for
+2°C to +150°C

(b) Circuit connection for -50°F to +150°F

Figure E12.14 ■ Circuit connection for the LM35

E12.15 The LM34 from National Semiconductor is a Fahrenheit temperature sensor with three
external connection pins. The pin assignment and circuit connection for converting the tem-
perature are shown in Figure E12.15. Use this device to construct a circuit to display the room
temperature in Fahrenheit. Assume that the temperature range of interest is from 240 o F to
215 o F. Use an LCD to display the temperature. Describe the circuit connection for a digital
thermometer that is made up of the HCS12 and the LM34, and write a program to display tem-
perature on the LCD.

+ V S
(+5 V to +20 V) V S

V OUT

Choose A

V OUT = +3000 mV at +300°F
= +750 mV at +75°F
= -500 mV at -50°F

R 1 = V S /50 μ

LM34 V OUT =

+10.0 mV/°F

LM34

R 1

- V S

(a) Circuit connection for
+5°F to +300°F

(b) Circuit connection for -50°F to +300°F

Figure E12.15 ■ Circuit connection for the LM34

E12.16 The Microbridge AWM3300V is a mass airfl ow sensor manufactured by Honeywell.
The block diagram of the AWM3300V is shown in Figure E12.16. It is designed to measure