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The first order of business was to decide which lamp to use. Naturally, I wanted the brightest, biggest, flashiest lamp I could easily obtain, so the natural candidate was a #906 bulb. (#906s are commonly used as flash lamps in WPC era pinball machines, and The Creature uses some of these.) However, as noted in this googley thread (started by myself! I guess that's a pretty good mark on when this project took flight!), there isn't enough room in the bumpers to put a #906 without changing the bumper caps.
The only problem with changing the caps on CFTBL is those dreaded ramps run right over the top of the bumpers. And by right over, I mean right over; you have less than an eighth of an inch clearance between the top of the cap and the ramps. So changing the caps was out, which means that the #906 bulb was also out.
So we were pretty much stuck with using either a #44 bulb or a #555 bulb. They produce roughly the same amount of light and heat, so I decided to go with the #555 since they're used all over the rest of the game.
Aside: Here's where the idiot in me starts to show itself. I'm calling myself an idiot because even though I went to school for umpteen semesters for electrical engineering, I only chose to remember some of what I learned. Don't worry; I didn't actually graduate as an EE; I wound up with a comp sci degree instead, so maybe the world is better off. :) But this is basic stuff, and I wound up making it harder than it needed to be. (Don't worry, this paragraph will start to make sense further down the page.)
So I grabbed my multimeter and took some measurements. First off, I grabbed an entire box of #555 bulbs and measured their resistance. (I told you, I'm an idiot! Those EEs of you out there, now you know why!) Average resistance of a #555 bulb was 2.3 ohms. Then I measured (with respect to the rails) the voltage the game normally puts across a #555 bulb; this turned out to be 9V. So I did a quickie ohm's law and figured out that the #555 bulb would have to be running ~3.91 amps through it when it was lit. I'm an idiot because I didn't instinctively realize that this is way too much amperage for a tiny little bulb like a #555 to handle!
So I did a little circuit analysis, and calculated that if I put in a large 14 ohm resistor in front of the light bulb, that ~4.4 amps of current would flow through the circuit. A little more than WMS pushes through the bulb, but a good starting point, so I decided to try it. I grabbed some 10W resistors from the Shack, fashioned up a 15 ohm resistor, and put the game into solenoid test mode.
WOW!!, that first flash sure was bright! Too bad there wasn't a second one. :( Needless to say, I cooked that bulb faster than Oprah eats pizza. Time to go back to the (sic) drawrering board.
So then I stumbled across Bill Ung's page on light bulb specifications. In there you'll notice that for a #555, in addition to listing it as a 6.3V bulb, it also lists the nominal current as 0.25A. Ah-ha! Now we have something to work with! Mr. Ohm, paging Mr. Ohm, please move your ass on over to my calculator. Quickie Ohm's law again says that the true resistance of a #555 should be ~25 ohms.
Then I did another circuit analysis; since I knew the #555 had approximately 25 ohms of resistance, and I knew WMS puts 9V across them, I figured out that WMS was pushing roughly 0.36 amps across them. This made sense, and was much more in line with the published specs.
Did another quickie circuit analysis, and figured that I needed ~175 ohms in front (or in back) of the light bulb (for a total resistance of 200 ohms) in order to get ~0.36 amps flowing through the circuit. Back to the Shack for some larger resistors, and away we go!
Except that it sucked! The light lit, but was very dim. Right about here is where I really start calling myself an idiot. You see, this would have worked, if the light in question wasn't wired in parallel with one bigass inductor (the pop bumper coil). I knew it was wired in parallel with a bigass inductor; I was the one who wired it! But I conveniently forgot to take that inductor into account in my calculations. So I'm an idiot for honestly thinking that my calculations would be anything close to the real world, when I knew darn well I hadn't modeled the real world correctly. (Get all that?)
So I had a choice; either I could find a signal generator and a scope, run it through a sweep of frequencies, calculate the inductor's true impedance, and then reanalyze the circuit and calculate a new resistor value to use. Or, since I knew that 15 ohms was far too little and 200 ohms was far too much, and had a whole boatload of power resistors from the (sic) Shark, I could step through (nay, guess even!) values from 15 to 200 ohms and maybe get lucky!
Well, that box of #555 bulbs gave its life for the project, but I finally hit on the right amount of resistance to use. :)
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