Matrix Hexpansion v2 (lite)

Status: designed and ordered but not yet assembled, tested, or linked to a badge app.

A versatile hexpansion breakout and co-processor board for prototyping or controlling many LEDs very cheaply.

This is the second and current version (see overview and comparison) marked v2 lite. Note the layout of the pads is not compatible with the v1 prototype.

BOM

Examples

Usage (with the generic badge app)

Status: badge software to be developed

Source files, pinout, and making a daughter board

Status: schematics and example boards will be published once the prototypes are confirmed working!

A daughter board for the matrix hexpansion does not need to be expensive: five copies of a typical board can be procured from regular PCB houses for about £5 (shipped). Unlike a regular hexpansion PCB, this does not need an edge connector or the more expensive ENIG coating. Of course, you still have to assemble it with your choice of size and count of LEDs (or pay for PCBA).

It must have space for the parent board footprint to be placed. The SMD version has pads on the bottom of the daughter board only and but may require a hot air rework tool and solder paste for assembly; there also is a through hole version for assembly with a regular soldering iron, the latter is also compatible with standard 2.54mm pin headers.

Example schematics for the charlie-plex wiring are provided for two different matrix layout options. The first joint-matrix example can drive 156 LEDs in 13 columns (with reduced brightness and refresh rate). The second dual-matrix has 72 LEDs in individual matrics of 7 and 6 columns (where most of the time, two columns are active at once).

In both cases, 13 resistors (one per GPIO pin or column) are required. Ideally, all LEDs should be the same colour to get more or less uniform brightness across the matrix. With the dual-matrix approach two colours may be used with different resistors on each set of column pins. However, brightness will also slightly reduce as more LEDs per column are active because the output voltage on the GPIO pins drops with higher current draw.

A 3D rendering of the v2-lite matrix hexpansion adapter board. The outline is the combination of half a hexagon with a flat top, joined with a rounded rectangle below the center line. At the top is the standard Hexpansion FPC connector. In the top left corner are four pads labelled -, SCL, SDA, +. In the top right corner are three pads labelled SWIO, -, +. At the bottom are three rows of rectangular pads described below. A top view is on the left, and the bottom view on the right. On the bottom layer there are a few solder jumpers explained below.

Pinout

There are three rows of 13 rectangular pads with 2.54mm spacing and 1.5mm round holes; the holes are larger than usual to facilitate soldering from the bottom side to another PCB to be placed on top of this one. Silkscreen labels mark the purpose of each pad, with the inverted labels indicating pins from the hexpansion connector, and the other pins being directly connected to the co-processor GPIO pins.

LSA PC0   PC1 (SDA) PC2 (SCL)   PC3 PC4 PC5   PC6 PC7   PA1 (LED) 3V3
LSB PD0   PD1 (SWDIO) PD2   PD3 PD4 PD5   PD6 PD7 (NRST)   PA2 (Config) GND
LSC LSD   3V3 GND   LSE HSF HSG   SDA SDA   HSH HSI

The first two rows contain all the GPIO and power pins for the co-processor and two low-speed badge pins. Perhaps excluding the two outer columns, this is expected to be used for boards that mainly display a matrix. This requires about 40×10mm of space at the top edge of the daughter board.

The third row has the remaining badge pins (four further low-speed GPIOs, all four high-speed GPIOs, power, and the I2C data and clock lines). It is intended for more general prototyping and can be used even if this board is not populated with a co-processor.

Special pins

There are some GPIO pins that can not be used as matrix outputs, leaving 13 that can (including PD7 unless used for badge interrupts). There are solder jumpers on the back of the board for these where it may make sense to disconnect them from their special use.