Thursday, March 19, 2009

Lighting (controlled)

After the Gi was done and working (pretty much a no-brainer - just connect it all up to 5v and you're laughing) it was time to move onto the controlled lighting. First thing I did was to wire up all the lights. I had picked up some phone cabling (i think) which had 4 cores through it. The controller IC's im going to use have 8 outputs, so that worked out well, just wire up two sets of 4 to each controller chip. The fact that the cables were grouped in 4 made the back side of the machine a lot neater (but probably not as neat as from the factory).

While all this was happening, i had ordered a basic stamp from parallax (www.parallax.com) - the bs2sx OEM model (OEM coz i didnt mind building it myself, and also it had a serial port built into it, as well as handy dandy outputs that i could plug into an IDE cable).

Link to the bs2sx: http://www.parallax.com/Store/Microcontrollers/BASICStampOEM/tabid/135/ProductID/501/List/1/Default.aspx

Next my main problem was that the basic stamp i chose has only 16 in/out pins for me to play with, which is well under the 43-or-so lights that i needed to control. I thought about a heap of solutions to this, such as an output matrix and flip flops, but the simplest solution is to do it the same way as the pinmame-hw guys - that is to use some separate IC's which are serial in, parallel out chips. 74HC4094 or 74HC595 (which as far as i can tell do the same thing, but with slightly different pinouts).

As it turns out, I had a handful of these chips still floating around from a previous failed attempt at making the pinmame HW circuit. The best move I made here was to purchase some breadboards and prototype the hell out of these things to get a good understanding of how they worked.


(Prototyping the IC's - i used an itermediate board between the basic stamp and the chips, connected by IDE cable - which the stamp fits into perfectly.)

I was basing my design off the pinmame-hw (but using the stamp instead of parallel port) which can be found here: http://membres.lycos.fr/regismalt/. Turns out that they got most of their HW info from another very handy site here: http://homepages.which.net/~paul.hills/Software/ShiftRegister/ShiftRegisterBody.html.

So after a heap of prototyping and soldering i finally had created my first prototype hardware board for the qbert pinball machine.

(Top of the light interface board)
(Rear of the board)

Pro-tip: use the chips to control transistors which allow current from an alternate power source, as i doubt the chips would be able to provide enough power to light all the lamps. Next post will cover some basic transistor theory!

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