Week #11: (4/1-5) ADCs & Rotary Encoders

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rjagodowski
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Week #11: (4/1-5) ADCs & Rotary Encoders

Post by rjagodowski » Sun Mar 31, 2019 7:34 pm

This week we're going to discuss two specific peripheral components: the ADC0831 which is used to convert an Analog voltage to an 8-bit digital quantity, and the Rotary Encoder which is commonly used to either measure rotation or used in place of the traditional potentiometer as an input device.

The datasheets for the ADC0831 and Rotary Encoder are attached below.
ADC0831_Datasheet.pdf
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27805-RotaryEncoderDataSheet.pdf
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In class on Monday, 4/1, you will receive a printed handout containing many of the individual documents linked here. Here is the pdf of that printed packet:
EET-260 ADC Notes 2019-0401.pdf
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NOTE: EET-260 Students who are not currently enrolled in EET-250, the discussion that follows relates to an application of the ADC chip used in their lab circuits.

The ADC chip outputs a serial 8 bit digital value for an applied analog input. This chip is used for many of the exercises in the EET-250 Control System Theory Process Control experiments. It's important to have a good understanding of how this chip functions for effective troubleshooting of those circuits. We will discuss the function of each of the pins on this 8-pin DIP IC. Special emphasis will be placed on the REF and VIN- pins to show who they can be used to get maximum resolution out of this chip.

Here is the Incubator Circuit you will build and test in lab which uses the ADC0831:
Here is an annotated picture of the schematic indicating important troubleshooting hints:
Annotated_Incubator_Schematic.jpg
Annotated_Incubator_Schematic.jpg (64.33 KiB) Viewed 73 times
Here is the annotated discussion from Chapter 6 in the Process Control Text from Parallax which explains the Signal Conditioning needed to get maximum useful resolution from the ADC0831. The signal conditioning, scaling and span topics discussed here are usually required of most ADC applications.
The Rotary Encoder:

The rotary encoder is commonly used in many applications now which used to use a potentiometer. The rotary encoder outputs a binary signal as the shaft is rotated. Unlike a potentiometer, the rotary encoder does not have any stops associated with its travel, so it can rotate indefinitely. It is bidirectional. The rotary encoder is connected to a microcontroller to interpret the rotary encoder's output and then act on its value.

Here's a link to State Electronics - Optical and Mechanical Rotary Encoders. Many of these operate by generating a quadrature signal. Here's a brief discussion on Encoder Measurements from National Instruments.com. For your convenience, a pdf of the NI tutorial is attached here as well:
NI-Tutorial-Encoder Measurement_7109-en.pdf
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