#847 2d6 Dice Roller

A little 1d6 or 2d6 dice roller using the TM1638 and ATtiny85.

Here’s a quick demo..

Notes

I have a number of games that require one or two 6-side dice. Rather than hunt for some dice or need space to roll them, how about a simple Arduino-based gadget?

Here are my basic requirements:

• Toggle between d6 or 2d6 die modes
• Roll with a button press: hold to shake and release to roll
• The “shake and roll” should be animated:
  • constant changing of the LED display while “shaking”
  • then decelerate to final value while “rolling”
• Auto-off? Rather than have on/off switch:
  • the unit should turn on when the die roll button is pressed
  • and auto-off after some delay (like 3 mins)
• Battery powered (no wires)

Technology selections:

• This is going to be an Arduino-based project:
  • prototype with Arduino Uno
  • perhaps final gadget using ATtiny85
• Final gadget power at 5V:
  • 9V battery with buck converter or 3V with a boost converter
• Use two 7-segment LEDs to represent the two dice
• LED driver:
  • options:
    • MAX7219 & SPI: can handle 2 digits with 3 pins for SPI
    • 2 x 74HC595 shift registers: can handle 2 digits with 3 pins
    • 2 x CD4026: can handle 2 digits with 2 pins
    • TM1638: LED control and button input with 3 pins
  • I’ve decided to use the TM1638, at least for a first prototype. It simplifies LED and push-button management, but I am not sure I can figure out a way for the push-button to also trigger the device wake-up.

LED 7-Segment Components

The 7-segment components I’m using here are similar to the SC56-11.

I’m using common cathode variants, so segments are wired to the TM1638 segment pins, and each digits cathode goes to the corresponding grid pin.

Arduino Uno Prototype Circuit Design

Designed with Fritzing: see 2d6.fzz.

The first prototype uses an Arduino Uno for convenience of programming.

This is working nicely. On startup, the die values are blank (“–”):

After a roll:

ATtiny85 Prototype Circuit Design

Designed with Fritzing: see 2d6-ATtiny85.fzz.

Reconfigured to use an ATtiny85. This mainly entailed modifying the microcontroller pin selection: 2d6.ino uses the ARDUINO_attiny definition to conditionally compile pin configurations based ont he processor.

Running nicely on the ATtiny85:

Auto-off?

I haven’t been able to figure out how to incorporate auto-power off without introducing another switch, or a different switch.

The SPST momentary push-button used for the “roll” function can’t also be used to trigger power-on, because it needs to be floating to be scanned by the TM1638.

Options:

• Replace the SPST with a DPST momentary push-button, but I don’t have any in my parts collection, and they appear to be quite an uncommon component at least in small footprint/low power.
  • Component options are limited, so this is not ideal
• Don’t use the TM1638 to scan the roll switch, read direct from the microcontroller
  • Becomes self-defeating: if I don’t use the TM1638 for the switches, then why use a TM1638 at all? Better to just use CD4026 or equivalent for the LEDs, and read the switches directly.
• Add another switch for power control
  • Unfortunately, perhaps the best option for a TM1638-based design.

Decision: I’m sticking with the TM1638, and since there’s no great solution for supporting auto-off, I’m going to scrap that idea for this version of the 2d6, and just use simple on/off switch.

I’ll probably do another version of the 2d6 with CD4026 instead of the TM1638 but with auto-off and no extra buttons or switches.

The Sketch

The program is organised as follows:

• 2d6.ino
  • main program loop
• Die.h / Die.cpp
  • models all operations for a single die
• TM1638.h / TM1638.cpp
  • TM1638 driver
  • doesn’t expose all capabilities of the TM1638, just enough to handle the two LED 7-segment displays and two buttons.
• KeyController.h / KeyController.cpp
  • models key states, using the TM1638 driver under the cover

Final Build

For the final build:

• 5V bench power supply replaced by 1xAAA battery and a 5V boost converter
  • Using a “0.9-5V To 5V DC-DC Step-Up Power Module Voltage Boost Converter Board 1.5V 1.8V 2.5V 3V 3.3V 3.7V 4.2V To 5V” (aliexpress seller listing)
  • Purchased for SG$1.74 including tax for 5 pieces (Nov-2024)
  • See LEAP#760 AAA 5v Power Pack for more on this module
• Transferred the circuit to 4x6cm protoboard
• Selected some more appropriate switches
• Mounted in a small wooden box I found at Daiso for SG$2

Updated design with Fritzing: see 2d6-ATtiny85-final.fzz.

Running nicely on the ATtiny85:

Here’s the protoboard layout:

Testing the circuit before final assembly:

Installed in the $2 wooden box from Daiso:

Testing, 2d6 mode:

Testing, 1d6 mode:

Conclusions and Next Steps

It’s a nice little gadget that gets the job done:

I was a little disappointed that I couldn’t figure out a good way to enable auto-off and reset with the roll button with the TM1368.

I will probably make some more die rolling projects:

• my partner immediately asked for a 3 die version!
• swap out the TM1368 for perhaps the CD4026, and do a true auto-off/single-button control version
• and perhaps a fully configurable multi-die roller with LCD or OLED display that can handle a wide variety of die configurations

Credits and References

• Titam TM1638 - info from the original manufacturer, Shenzhen Titan Micro Electronics Co., Ltd. (深圳市天微电子股份有限公司)
• “0.9-5V To 5V DC-DC Step-Up Power Module Voltage Boost Converter Board 1.5V 1.8V 2.5V 3V 3.3V 3.7V 4.2V To 5V” (aliexpress seller listing)
  • Purchased for SG$1.74 including tax for 5 pieces (Nov-2024)
  • See LEAP#760 AAA 5v Power Pack for more on this module