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Knob Board

This document describes the design considerations and implementation details for the AMDC Knob (Encoder) expansion board. A block diagram is presented to explain each component in detail.

Relevant Hardware Versions

  • AMDC REV D with Knob Board REV A
  • AMDC REV E with Knob Board REV A

How To Use

After the AMDC is flashing sequentially and properly working in debug mode (See this link for set up) attach a DB9 connector between the AMDC GPIO pins and the Knob Board.

To get discrete values from the encoder use the following commands in the Xilinx IDE:

  • hw enc steps - Read encoder steps from power-up
  • hw enc pos - Read encoder position
  • hw enc init - Turn on blue LED until Z pulse found (Not Currently Functional)
  • hw enc zval - Read switch presses from power-up (Not Currently Functional)

In Progress And Future Work

The Knob Board does not currently support the Encoder's switch feature. An additional register must be allocated in the code and bitstream for this to work.

The Knob Board may work with a DB15 connector, however, this will also require additional work to implement.

Proof of Concept Using LEDs: (Not Optimized) Copy the code found here to the corresponding locations in your project. Note that the hw/amdc_revd.bd file does not need to be copied for the hw enc steps and hw enc pos commands to work, however, this code is set up to also test the hw enc zval command which may cause issues. Additionally this code was set up using a AMDC REV D

Design Requirements and Considerations

The AMDC Knob expansion board was designed with the following requirements:

  1. Allow for an additional input to the AMDC

  2. Works with DB-15 and DB-9 connectors

  3. Designed to run off of 5V power supplied from the AMDC

  4. Minimize noise with debouncing and a Signal Differentiator

AMDC Connector

The AMDC Knob expansion board interfaces with the AMDC via either the DB-15 (GPIO) connector or the DB-9 (encoder) connector. The pinouts of the two connectors differ from one another as shown in the tables below.

DB-15 Connector

Pin Number Power Stack
1 5V DB-15
2 Encoder 1A
3 Encoder ~1A
4 Encoder 1B
5 Encoder ~1B
6 No Connect
7 Encoder 1Z
8 Encoder ~1Z
9 No Connect
10 No Connect
11 GND
12 No Connect
13 No Connect
14 No Connect
15 No Connect

DB-9 Connector

Pin Number Power Stack
1 Encoder 1A
2 Encoder ~1A
3 Encoder 1B
4 Encoder ~1B
5 Encoder 1Z
6 Encoder ~1Z
7 5V DB-9
8 GND
9 GND

Both the DB-15 and DB-9 connectors can be connected to the Knob expansion board, however, the single jumper on the Knob board ensures power will only be pulled from one of the connectors.

PCB Layout

Two polygon pours were used to reduce the number of required traces. The top pour is the +5V net, and the bottom pour is the GND net. All components and most traces are also located on the top of the board to simplify the fabrication of the board. Additional PCB properties are outlined in the table below.

Property Value
Size 70mm x 80mm
Number of Layers 2
Thickness 1.6mm
Min Track/Spacing 6/6mil
Min Hole Size 0.3mm
Surface Finish HASL (Tin-Lead)
Silkscreen Top Only
Unique Part Count 9
Unique SMD Part Count 5
Total Parts 17
Through-Hole Count 53
Cost per Board (Unit 1) $8.64
Cost per Board (Unit 10) $7.17

LPFs

Low pass filters such as the one shown below are used throughout the Knob expansion board. These low pass filters are used to prevent debouncing while still allowing for signals to be sent at a rate of 160 times per second.

The cutoff frequency is achieved based on the resistance and capacitance values of the filter:

f_c = 1 / (2*π*R*C)

The LPF’s cutoff frequency is set to 160Hz (a resistor with R = 10kΩ and a capacitor with C = 0.1μF achieves the desired frequency).

Datasheets