Atmel ATmega32M1 Manual page 260

19.2.2 Current Source for Low Cost Traducer
19.2.3 Voltage Reference for External Devices
Atmel ATmega16/32/64/M1/C1
260
Table 19-2. Example of Resistor Values(±1%) for a 16-address System (AV
Physical Resistor Value
Address R (Ohm)
load
0 1 000
1 1 200
2 1500
3 1800
4 2200
5 2700
6 3300
7 4700
8 6 800
9 8 200
10 10 000
11 12 000
12 15 000
13 18 000
14 22 000
15 27 000
Note: 1. 5V range: Max R
3V range: Max R
An external transducer based on variable resistor can be connected to the Current Source. This
ca be for instance:
• A thermistor, or temperature-sensitive resistor, used as a temperature sensor
• A CdS photoconductive cell, or luminosity-sensitivity resistor, used as a luminosity sensor.
Using the Current Source with this type of transducer eliminates the need for additional parts
otherwise required in resistor network or Wheatstone bridge.
An external resistor used in conjunction with the Current Source can be used as voltage refer-
ence for external devices. Using a resistor in serie with a lower tolerance than the Current
Source accuracy (≤ 2%) is recommended.
using standard values of resistors.
Typical Minimum
Measured Reading with
Voltage (V) a 2.56V ref
0.1 38
0.12 46
0.15 57
0.18 69
0.22 84
0.27 104
0.33 127
0.47 181
0.68 262
0.82 316
1.0 386
1.2 463
1.5 579
1.8 694
2.2 849
2.7 1023
30KΩ
load
15KΩ
load
Table 19-2
CC
Typical
Reading with
a 2.56V ref
40
48
60
72
88
108
132
188
272
328
400
480
600
720
880
1023
gives an example of voltage references
(1)
= 5V )
Miximum
Reading with
a 2.56V ref
45
54
68
81
99
122
149
212
306
369
450
540
675
810
989
1023
7647H–AVR–03/12