Datasheet

190
7728G–AVR–06/10
ATtiny87/ATtiny167
16.2.2 Current Source for Low Cost Transducer
An external transducer based on a variable resistor can be connected to the Current Source.
This can be, for instance:
• A thermistor, or temperature-sensitive resistor, used as a temperature sensor,
• A CdS photoconductive cell, or luminosity-sensitive 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.
16.2.3 Voltage Reference for External Devices
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. Table 16-2 gives an example of voltage references
using standard values of resistors.
16.2.4 Threshold Reference for Internal Analog Comparator
An external resistor used in conjunction with the Current Source can be used as threshold ref-
erence for internal Analog Comparator (See ”AnaComp - Analog Comparator” on page 211.).
This can be connected to AIN0 (negative Analog Compare input pin) as well as AIN1 (positive
Analog Compare input pin). Using a resistor in serie with a lower tolerance than the Current
Source accuracy (≤2%) is recommended. Table 16-2 gives an example of threshold references
using standard values of resistors.
16.3 Control Register
16.3.1 AMISCR – Analog Miscellaneous Control Register
• Bit 0 – ISRCEN: Current Source Enable
Writing this bit to one enables the Current Source as shown in Figure 16-1. It is recommended
to use DIDR register bit function when ISRCEN is set. It also recommended to turn off the Cur-
rent Source as soon as possible ( ex: once the ADC measurement is done).
Bit 76543210
- - - - - AREFEN XREFEN ISRCEN AMISCR
Read/Write RRRRRR/WR/WR/W
Initial Value 00000000