You can not select more than 25 topics
Topics must start with a letter or number, can include dashes ('-') and can be up to 35 characters long.
139 lines
4.4 KiB
139 lines
4.4 KiB
# Electronic Dice with AVR
|
|
|
|
The idea is pretty straightforward, hardware is simple, but it's still darn
|
|
cool!
|
|
|
|
The project is built around ATTiny13, but you can of course use any bigger chip
|
|
or even arduino, but it'll really be overkill. It's not making full use even of
|
|
the few peripherals the ATTiny13 provides!
|
|
|
|
|
|
## What it does?
|
|
|
|
Really simple, you have a couple LEDs that represent dots on a dice, and one
|
|
button.
|
|
|
|
When the button is down, the numbers quickly spin, and when you release
|
|
it, they slow down to a crawl, then the number blinks a few times and that's an
|
|
indication that your roll is complete.
|
|
|
|
When the dice is idle for 5 seconds, it goes to sleep (can be woken by pressing
|
|
the button). The delay can be customized in the source file.
|
|
|
|
|
|
## Hardware
|
|
|
|
The dice is not really challenging on the hardware side.
|
|
|
|
All you need is 7 LEDs with resistors, one button, and obviously the AVR.
|
|
You can also add a power switch, but it's not really needed, since the dice
|
|
is smart enough to sleep when it's not used.
|
|
|
|
It can be powered by any DC source, 3..5V. Three AA batteries in series can do
|
|
the trick, four AA's won't hurt anything as well - the chip is quite durable
|
|
if you don't overdo it.
|
|
|
|
Cunsumption when lights are on is (with my LEDs and 180R resistors) somewhat
|
|
around 50 mA, in sleep mode it's negligible (< 1 uA if my meter can be trusted).
|
|
|
|
|
|
### Pinout
|
|
|
|
```
|
|
+--u--+
|
|
RST --| |-- Vcc
|
|
SEG_DIAG2 : PB3 --| t13 |-- PB2 : SEG_DIAG1
|
|
SEG_HORIZ : PB4 --| |-- PB1 : SEG_DOT
|
|
GND --| |-- PB0 : BUTTON
|
|
+-----+
|
|
```
|
|
|
|
|
|
### Placement of the LED segments
|
|
|
|
One could think that using 7 pins for 7 leds is needed, but in fact, you can use
|
|
just four - which is great, since ATTiny13 has only 5 I/O pins (unless you use
|
|
the reset pin as I/O, but that's quite uncommon).
|
|
|
|
```
|
|
|
|
(DIAG1) (DIAG2)
|
|
|
|
(HORIZ) (DOT) (HORIZ)
|
|
|
|
(DIAG2) (DIAG1)
|
|
|
|
```
|
|
|
|
|
|
### Wiring of the segments
|
|
|
|
In the project, LEDs are connected by anodes to the pins. It's okay,
|
|
since the chip can handle it just fine, but you may want to connect them by
|
|
cathode instead (useful for greater loads).
|
|
|
|
To do so, adjust the `show()` routine accordingly (there's an explanatory
|
|
comment included). Basically, just negate the output states, and you're good.
|
|
|
|
```
|
|
DOT sengment:
|
|
|
|
PIN ---> LED -> RESISTOR ---> GND
|
|
|
|
|
|
Other segments:
|
|
|
|
PIN -+-> LED -> RESISTOR -+-> GND
|
|
| |
|
|
'-> LED -> RESISTOR -'
|
|
|
|
Button:
|
|
|
|
PIN --> BUTTON --> GND
|
|
```
|
|
|
|
|
|
## The program
|
|
|
|
Now that you have your dice hardware assembled, let's move on to the fun part -
|
|
the software.
|
|
|
|
You can of course just grab it from the repository, compile, flash and be done
|
|
with it, but I think it's useful to explain how it works.
|
|
|
|
Feel free to tinker with the source, add extra effects etc, it's fun!
|
|
|
|
|
|
### Generating random numbers
|
|
|
|
Firstly, we don't use any hardware entropy, or even a random number generator.
|
|
That may sound odd, but it's in fact not really needed.
|
|
|
|
The core idea is that the button is never pressed at the same time and for the
|
|
same duration. So, we can easily spin a counter when the button is down, and
|
|
when it's released, we pretty much already have our random number.
|
|
|
|
To add more randomness, there's also a second, "entropy" counter, that spins all
|
|
the time (unless, of course, the dice is sleeping), and when the button is
|
|
pushed, the value from this "entropy" counter is copied to the main counter.
|
|
The idea is that people can't cheat by somehow managing to press the button
|
|
for the exact same time.
|
|
|
|
Note, that those counters are just ints incrememnted and wrapped by the program
|
|
- we don't have to use of the hardware timers for this.
|
|
|
|
|
|
### Sleep mode
|
|
|
|
When the dice is inactive for five seconds (that is, no animation and
|
|
interaction), it automatically enters a POWER DOWN sleep mode.
|
|
|
|
Clearly, going to sleep without a way to wake up would be silly. Therefore, it
|
|
also enables a Pin Change Interrupt right before entering the sleep mode, so a
|
|
button press will wake it up. The cool thing is that it immediately starts
|
|
spinning the numbers and resumes normal operation.
|
|
|
|
Note, that the dice also starts into the sleep mode, so when you power it on,
|
|
it will sleep until you press the button. This is important, because I didn't
|
|
like the idea of showing the same number it starts - this way, you randomize it
|
|
right away by the first button press.
|
|
|