Debu's Innovations: January 2009

Not too long ago, during a game of Monopoly, I thought to myself; "How the hell do I always end up loosing? I bet these dice are loaded!", and right then the geeky idea of building my own digital dice was born.

Idea
The Idea was to build a dice that:

Produced 100% random result
Easy to use, Simple button press and ... result
Small enough to carry around with a board game
Low power consumption, should run on battery power for long
Ensure that every one knows that you are a geek ;)

Construction
The hardware is based on an ATTiny 2313 processor, the main features of the hardware:

Processor: AVR, ATTiny 2313.
7-Segment LED display (common anode) to display the digits.
Thumb Switch to take input from the user

Thumb Switch
Battery as source of power.

So, first I designed the hardware as per the schematics above onto a simple breadboard.

No Problem, simple circuit. I used headers to connect the 7-Segment LED display, this way, I could remove the display as and when required.

Ok, That's done! Now to work on the battery and regulator circuit. Here I decided to use a LM7805 regulator, along with a 1000uF and a 100uF capacitor, to deal with the casual drop in voltage when the circuit starts drawing current. I used common 9V 6LR61 batteries to power the regulator.

For the casing, I got some thin and light ABS Plastic pieces from my throw away waste.

I cut and filed them to a somewhat desirable size.

Drilled a nice hole for thumb switch.

And.....Done!

Software
I wrote the code for the processor in assembly, what I am showing here is only the skeleton structure. The complete code is available in the download package.

First is the Reset Vector ,GetButtonPress and the ButtonPressed routines:

   1: .include "tn2313def.inc"   2:     3: .org 0x0000   4:     RJMP Reset    //Code Starts from Address 0x0000   5:     6: Reset:            //Reset Vector   7:     RJMP Init   8:     RJMP GetButtonPress   9: RJMP Reset  10:    11: GetButtonPress:  12:     SBIC PORTD, 3        //Skip if Bit is Clear on PD3  13:     RJMP GetButtonPress    //Relative Jump to Label  14:     RJMP ButtonPressed    //Relative Jump to Label  15: RJMP GetButtonPress  16:    17: ButtonPressed:  18:     SBIC PORTD, 3      //Skip if Bit is Set on PD3  19:     RJMP ShowResult      //Relative Jump to ShowResult  20:     INC    R17                //Increment Register R17  21:     INC    R16                //Increment Register R16  22:     CPI    R17, 0xFF       //Compare Immediate R17 and 0xFF  23:         BREQ ToggleDP //Branch if Equal to ToggleDP  24:     LDI R18, 0x06     //Load R18 with with Immediate 0x06  25:     CPSE R18, R16      //Compare, Skip if Equal  26:     RJMP ButtonPressed//Relative Jump to ButtonPressed  27:     CLR    R16              //Clear Register R16  28: RJMP ButtonPressed

The skeleton routine above does not take into account the debounce of the thumb switch. The thumb switch being used is spring loaded, and has a magnetic catch inside it, so the typical debounce would be around ~80ms. Now, running at 8MIPS (internal RC oscillator), in terms of processor cycles, that would be; 1 sec = 8,000,000 instructions; 1ms = 8,000 instructions; 80ms = 64,000 instructions; That means we need to call nop 64,000 times to debounce the switch correctly.

Next we have the ShowResult routine. This basically displays on our 7-Segment display the value of the roll.

   1: ShowResult:   2:     LDI    R18, 0x01    //Load Immediate R18, with 0x01   3:     CP    R16, R18    //Compare R16 and R18   4:         BREQ ShowOne//Branch if Equal to ShowOne   5:     LDI    R18, 0x02    //Load Immediate R18, with 0x02   6:     CP    R16, R18    //Compare R16 and R18   7:         BREQ ShowTwo//Branch if Equal to ShowOne   8:     LDI    R18, 0x03    //Load Immediate R18, with 0x03   9:     CP    R16, R18    //Compare R16 and R18  10:         BREQ ShowThr//Branch if Equal to ShowOne  11:     LDI    R18, 0x04    //Load Immediate R18, with 0x04  12:     CP    R16, R18    //Compare R16 and R18  13:         BREQ ShowFou//Branch if Equal to ShowOne  14:     LDI    R18, 0x05    //Load Immediate R18, with 0x05  15:     CP    R16, R18    //Compare R16 and R18  16:         BREQ ShowFiv//Branch if Equal to ShowOne  17:     LDI    R18, 0x06    //Load Immediate R18, with 0x06  18:     CP    R16, R18    //Compare R16 and R18  19:         BREQ ShowSix//Branch if Equal to ShowSix  20: RJMP ShowResult

One more important consideration here is Low Power Mode, and automatic turn off (We are running on batteries here, after all). In the final code, I have included a low power and auto turn of routine. This checks to see if the dice is not used for 4 Seconds or more, and then turns off the display and puts the processor and other peripherals in a low power state. See the video of operation below to get a good idea of how this works.

Ok, thats it!! All Done now!!

And it Works!! :D