Table 19-1. Example of Resistor Values (±5%) for a 8-address System (AVCC = 5V(1))
Physical
Address
Resistor Value
Rload (Ohm)
Typical Measured
Voltage (V)
Minimum Reading Typical Reading Maximum Reading
with a 2.56V ref
with a 2.56V ref
with a 2.56V ref
0
1
2
3
4
5
6
7
1 000
2 200
3 300
4 700
6 800
10 000
15 000
22 000
0.1
0.22
0.33
0.47
0.68
1
40
88
132
188
272
400
600
880
1.5
2.2
Table 19-2. Example of Resistor Values (±1%) for a 16-address System (AVCC = 5V1))
Physical
Address
Resistor Value
Rload (Ohm)
Typical Measured Minimum Reading Typical Reading Miximum Reading
Voltage (V)
with a 2.56V ref
with a 2.56V ref
with a 2.56V ref
0
1
1 000
1 200
1500
0.1
38
46
40
48
45
54
0.12
0.15
0.18
0.22
0.27
0.33
0.47
0.68
0.82
1.0
2
57
60
68
3
1800
69
72
81
4
2200
84
88
99
5
2700
104
127
181
262
316
386
463
579
694
849
1023
108
132
188
272
328
400
480
600
720
880
1023
122
149
212
306
369
450
540
675
810
989
1023
6
3300
7
4700
8
6 800
8 200
10 000
12 000
15 000
18 000
22 000
27 000
9
10
11
12
13
14
15
1.2
1.5
1.8
2.2
2.7
Note:
1. 5V range: Max Rload 30K
3V range: Max Rload 15K
19.2.2 Current Source for Low Cost Traducer
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.
19.2.3 Voltage Reference for External Devices
An external resistor used in conjunction with the current source can be used as voltage reference for external devices. Using
a resistor in serie with a lower tolerance than the current source accuracy (≤ 2%) is recommended. Table 19-2 gives an
example of voltage references using standard values of resistors.
ATmega16/32/64/M1/C1 [DATASHEET]
223
7647O–AVR–01/15
MICROCHIP [ MICROCHIP ]
