The Joey board from Gooligum Electronics is a nifty 4-digit LED display that is designed to press-fit onto the first 26 pins of a Raspberry Pi. The holes on the PCB are slightly offset from a standard 2.54mm grid so that the pin-to-hole friction maintains the contact. Besides LEDs, there are 3 pairs of male headers which can be used for switch input. A Holtek HT16K33 controller handles all the 7 segment interfacing requirements. See this Kickstarter page for background information.
Python code support is available from their github site and I have created a C++ class library here for Arduino. For this project, an ESP-32 was connected to Joey but the code should work on any microcontroller supported by the Arduino framework eg ATmega328, STM32, etc.
Note: Adafruit LED Backpack library which also supports the Holtek HT16K33 chip does not play well with this board. The library uses 8 contiguous bits in the display buffer for each digit whereas Joey uses 16 bits to map the segments. As a result, the Adafruit's sevenseg test program show digits with missing segments.
| Joey Pin | Name |
|---|---|
| 1 | 3.3V |
| 2 | 5V |
| 3 | SDA |
| 4 | |
| 5 | SCL |
| 6 | GND |
Sample applications which uses the Joey_LEDBackpack class library are found under the examples directory. Clone this repository and and unzip to your .../Arduino/libraries folder.
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RandomNumbers.ino - Display various patterns on the 4-digit LEDs depending on jumper settings.
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ShowAll.ino - Light up every segment on the Joey board in a loop and show corresponding pin-to-segment mappings in the serial monitor. Very useful debug tool.
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ReadKeys.ino - Read the state of the jumpers (JP1-JP3) and light up a dot. The jumpers are the functional equivalent of a DIP switch.
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sevenseg.ino - Adafruit LED Backpack sevenseg example modified to instantiate Joey_7segment class instead of Adafruit_7segment. No other changes required.
