A couple of weeks ago the lovely Lisa Mather (party planner extraordinaire) put out a request on Twitter for party games. This was for the Manchester Raspberry Jamboree after party on the 28th February (more on the jam in my next post).

So, having already cobbled the basic Snake game together in December I offered to polish it up a bit and add scoring functionality. In addition I felt it needed a better control interface than the keyboard, so a quick shout out to some local friends and I had a Quickshot II+ from a Spectrum ZX81 – it even has the clicky micro switches that any child of the 80’s instantly recognises – mmmmm, retro.

The core code from my last post hasn’t changed much, the main differences are;

• swapping keyboard input routine for GPIO pins detection – one for each switch in the joystick (up/down/left/right/fire)
• implementing code to record scores (1 point for each piece of food) and using two of the 4x seven segment displays from the Delorean Time Circuit for displaying them

Wiring was a pig (as you can see), but worth it in the end; even if I did have to do some gorilla soldering on Friday when a couple of leads came loose.  I highly recommend buying at least the 8×8 grid as a PCB kit (e.g. Pimoroni or CPC) to save your sanity.  The desoldering of the seven segments and subsequent wiring you see here took me a goodly portion of my Sunday afternoon 🙁

In the picture you can see 5 (extra chunky) resistors on the breadboard.  These are being used to pull the GPIO pins low (or off).  As the joystick is moved, the internal switches will complete the circuit with the +3.3v line (red wires) which will set the attached pin high (or on).  This is detected by the code and the snake moves the chosen direction (if it’s allowed to of course).

The game had a lot of interest and went down well with young and young at heart. The high score went to both Oliver (who achieved it first) and Michael with a score of 22!

Chris (3rd – 21) Michael & Oliver (1st – 22)

[updated source to follow]

One of the other things the Adafruit LED Backpacks are bundled with is an 8×8 LED matrix.  As I no longer needed my Time Circuit project I removed a backpack from the setup and ordered a Red/Green matrix from CPC.  I purposely bought the bi colour matrix as the red, green and yellow (r+g) gives me scope to play around more.

So what first?  Well, I needed to wire it up; and as I am using the Adafruit Python libraries again I need to make sure the red and green pins were wired according to their code (red = a0 – a7, green = a8 – a15).  To make sure everything was in order I ran the example Python code from the library which cycles through each LED in red, green then yellow.

Let’s Code
In my code there are four main variables

snake – a list object containing the x,y coordinates of each piece of the snake at any one time. These are in head to tail order.

food – contains the x,y coordinates of the current ‘food’ block on the display

direction – a string that holds the direction of travel of our snake r(ight), l(eft), u(p) or d(own)

grid – an instance of the Adafruit 8×8 grid library

The main function then has the following actions:

• Check for key press; see if we need to change direction
• Identify the next square the snake will move to
• Check to see if it’s hit the edge or itself
• Check to see if we’ve ‘eaten’ the food
• Update the snake object to move it on one square
• Draw the snake

To manage the snake the list object is used as a queue or First In First Out, aka FIFO, structure (that’s a proper programming term and everything kids!).  So every move is done in two steps,  insert the new head location into the first position (or push) and remove (or pop) the last item in the queue.  

Before the insert happens the new coordinate is checked to see if we need to do anything special.  

• If the new head is outside the grid (hit the edge) or is the same location as part of the snake body then the code walks the snake list object and turns each coordinate red.
• If the snake eats the food then the tail coordinate stays on the queue, extending the body by 1

That’s about it really.  The only other thing to note is that without using PyGame and an interactive screen capturing the keys is not quite as straight forward as you would hope.  There are two functions keyPress and control that I borrowed from the interwebs (there’s stacks of examples) to capture the key presses on a separate thread so that the main display loop (move snake, redraw etc) doesn’t hang waiting for a key press.

Source Code

Well, this is why this blog exists (for the moment at least).  Go read, I hope it’s useful, but I can’t guarantee it will get you to 88mph or the year 1955.  However if you hang around for about 700 days it might get you to 2015 🙂