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Avr analog ground4/26/2023 The inputs are sampled periodically at a low duty cycle as the sampling duty cycle affects cross talk among the inputs. Most of the time, the circuit is in the “filtering” sate (see the illustrations above). This allows the pin to be held at ground and then ungrounded when using it as an input for the comparitor. In the case of many AVR controllers, the input of the comparitor shares a pin with a bidirectional I/O bit. The technique takes advantage of bidirectional I/O ports to switch from outputs to inputs. The resistor-capacitor combination form a low pass filter and switching of the charged capacitor is the means by which multiplexing is effected. Notice that for each analog input, there is a 100k resistor, a. The AT90S1200A used for the test has a single comparitor, but an analog multiplexer was formed using two of its digital bidirectional I/O ports. When a test voltage exceeds the reference voltage, the LED corresponding to that particular test voltage lights, demonstrating that the two sampled channels are independent. The test circuit (schematic below, photograph above), when running the associated firmware ( click here to see the assembler code (file name “hfcm030602.asm” ), compares two test voltages, appearing on the wires of the 10k pots, with a reference voltage, which appears on the wiper of the 50k pot.
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