SPI-POTX2

Features

• Dual Digital potentiometer
  • MCP4231 Dual Digital Pot
  • 7-bit: 128 Resistors (129 Steps)
  • Zero Scale to Full Scale Wiper operation
  • 10K
    • Other resistances optional: 5K, 50K, 100K
  • Power on reset to half wiper value
  • SPI Interface
    • SPI Serial Interface (10 MHz, modes 0,0 & 1,1)
    • High-Speed Read/Writes to wiper register
    • 10 MHz (max SPI speed)
• 2.7V to 5.5V
• Daisy-chain SPI connector
  • Slave Select (SS) should be star connected
• 49x49mm form factor
• (4) #4-40 mounting holes

Connectors

J1, J3 - SPI connector - Rev X1

• Two separate 1x5 headers
  • Used for chaining to other cards

1. MISO
2. +V
3. SCK
4. MOSI
5. SS
6. GND

J1, J3 - SPI connector - Rev 2

• Single 2x6 right angle header
  • Used for chaining to other cards

1. MISO
2. +V
3. SCK
4. MOSI
5. SS
6. GND

J2 - SPI Connector

• Matches Arduino SPI connector pinout

1. MISO
2. +V
3. SCK
4. MOSI
5. SS
6. GND

POT0

1. GND
2. B SIDE
3. WIPER
4. A SIDE
5. +V

POT1 - Rev X1

1. GND
2. A SIDE
3. WIPER
4. B SIDE
5. +V

• Rev X1 board has POT1 A, B Sides reversed on Silkscreen
  • Impacts POT1 Vcc/GND jumpers

POT1 - Rev 2

1. GND
2. B SIDE
3. WIPER
4. A SIDE
5. +V

• Rev 2 board updated so POT1 matches POT0

Driver Software

• Set channel number on GPIO_22 (A0), GPIO_27 (A1), GPIO_17 (A2)
• Do SPI transfer as 2 of 8-bit or 1 of 16-bit transfer(s)

Arduino Driver / Example Code

• SPI-POT-X2 GitHub Arduino Example Code
  • Creates triangle wave output on both outputs

Raspberry Pi Example Code

• Test SPI-POTX2 Dual pot card on the Raspberry Pi using RPI_SPI8 SPI mux card
  • Mux card is easy to include/exclude option in the code

# Set the next line to False if directly connecting to Raspberry Pi SPI bus
USING_RPI_SPI8_CARD = True

• Makes triangle waves on the pot wiper pins
• MCP4231_SPI_Test.py - Our GitHub repo
  • Readme file

Raspberry Pi Reference Docs

• SPI on the Raspberry Pi
• Python Spidev

Factory Test Procedure

• Test SPI-POTX2 card on RPI_PSOC5 Test Station

Hardware Setup

• RPI_PSOC5
  • Raspberry Pi CPU Clone
• RPI_SPI8
  • 8-channel SPI multiplexer
• Unit Under Test (UUT)

SPI Cable

RPI_SPI8 (Marking)	RPI_SPI8 Pin	SPI-POTX2 Pin	SPI-POTX2 Marking
Chip En (CE)	1	5	SS
MOSI (MO)	2	4	MOSI
MISO (MI)	3	1	MISO
SPICK (CK)	4	3	SCK
Vcc (+V)	5	2	+V
GND	6	6	GND

Run Tests

• Run puTTY
  • Find COM Port in Device Manager
  • 115,200 baud
  • RTS/CTS flow control

• Hit ENTER to see menu

Land Boards, LLC - RPi Card Test Station
1 - Select RPP-UIO-16 Card
2 - Select RPPSOC Card
3 - Select RASPI-PLUS-GVS-CFG Card
4 - Select RASPI-GVS Card
5 - Select RASPI-PLUS-GVS Card
6 - Select RPI-I2C-HUB Card
7 - Select RPI-SPI8 Card
8 - Select SPI-POTX2 Card (via RPI-SPI8)
R - Read EEPROM
W - Write EEPROM
B - Bounce LED across Card GPIOs
T - Test Card
D - Debug Card
? - Print this menu

• Select SPI-POTX2 Card by entering 8[ENTER]

8
Selected SPI-POTX2 card (vis RPI-SPI8)

Create Sawtooth Output

• Enter T[ENTER] - Create ramped output

Testing SPI-POTX2 card (via RPI-SPI8), please wait
test_SPI_POTX2() - Reached function
test_SPI_POTX2() - Start SPI
test_SPI_POTX2() - Started SPI

• Use scope to observe ramped output on POT0
  • CH 1 Yellow = SPI_CE0
  • CH 2 Cyan = POT0 wiper

Test Software

• Runs on RPI_PSOC5
• GitHub repo
  • Test_RPI_SPI8.c - Bounce LED across LED-TEST-2 card

• Runs on RPI_PSOC5
• Uses RPI_SPI8
• GitHub repo
  • Test_RPI_SPI8.c - Test with SPI-POTX2 card

Changes

Rev 2

• Swapped POT1 A, B pins to match POT0 and silkscreen
• Combined SPI connectors from 2 to 1 of 2x6 connector
• Added SPI pin names to reverse side silkscreen

Rev X1

• POT1 A, B pins swapped on silkscreen
  • POT1 Vcc, GND taps can not be shunted directly - need jumper cables to correct

Assembly Sheet

• SPI-POTX2 Rev 2 Assembly Sheet
• SPI-POTX2 Rev X1 Assembly Sheet