This is the project for bubbledisp, a small carrier PCB for five-digit HP bubble displays. In particular I used the HP QDSP-6061 but most datasheets I've seen for five-digit displays are compatible.

It is the first PCB that I designed myself and manufactured at AISLER. After a previous project that I hand-soldered on protoboard – which is not yet documented anywhere – I wanted to miniaturize the board and have a universal display, which speaks whatever protocol that suits my needs best.

So this little circuit board is basically that: flip the slider switch on the right to speak I2C, UART or SPI and connect it in your development environment.

The hardware part is documented in hardware. Particularly, you can find the schematic and Gerber files there. The project was created with EasyEDA online.

A compatible display can still be found on eBay. Search for "HP QDSP" or "bubble display".

The pullups R11 and R10 are optional if you don't want to use I2C or have external pullups somewhere else. They don't hurt though and UART and SPI both work fine with pullups, too.

Otherwise, VCC is connected directly to the ATmega328PB, so the specifications from the datasheet directly apply: i.e. use 3.3 V or 5 V with appropriate logic levels.

The firmware still needs some work but all the protocols kind of work. The I2C protocol is the most functional one as of now.

It is a PlatformIO project in firmware. First set the fuses and then flash the firmware:

pio run -t fuses
pio run -t program

You may need a pogo-pin adapter to properly make contact with the ICSP pads on the bottom side.

Select the protocol you wish to use before powerup. The switch is only checked once inside setup().

The node address is configured as I2C_ADDRESS in main.ino and is currently 0x32 by default. The pinout is as follows:

Currently only three ports are available for writing:

The text input uses a simple translation map, that can be seen in segments.h. Most of the alphabet, numbers and a few symbols work.

For the raw segment input, refer to this ASCII graphic from segments.h:

                            a
     Ad╶┐┌╴Ae             ────
    Ac╶┐││┌╴Af         f │    │
   Ab╶┐││││┌╴Ag          │  g │ b
  Aa╶┐││││││┌╴Adp  ❯❯     ────
   0b00000000          e │    │
                         │    │ c
                          ────
                            d   ■ dp

For example, using a i2c-tiny-usb and the i2c-tools on a Linux computer:

The UART mode is configured as 8N1 with 57600 baud. You can try setting UART_SPEED higher but those speeds are not guaranteed to work with the internal RC oscillator.

There is not much happening on TX as of yet, so you can use UART with just three wires. All input is interpreted as text and a newline clears the line and resets the cursor to the first digit. If more than 5 characters are sent without a newline the text scrolls off to the left.

Beware, here be dragons.

SPI is pretty buggy still because I didn't realize that SS is necessary for proper synchronization. As the hardware SPI will refuse to work when SS is not pulled low, a very crude software implementation is currently used. This however easily loses sync so that any following input is garbled. Meh'.

For the above reasons there's no documentation yet. Improvements are welcome!

A few more pictures: