1/19/2015, Backboxes, Playfields and Screens, oh, my!

A couple weekends ago, I finished populating the playfield.  While not a Herculean task, it was a little bit annoying since I filled all post holes because they were almost all pulling out and not holding properly.   After the clearcoat, I used a nail to punch the center of the bamboo skewer, than a small drill bit to drill the pilot hole.  It went surprisingly well, and I’m now happy to report that the playfield is probably in better shape than it has been for 15 years.  Here is a quick picture of the populated playfield.


I decided I wasn’t going to fire up the playfield again until I got the backbox in better shape.  A couple weeks back I installed the power supplies, and the MaxPower card that creates my 48V.  (On a side note, Joe just bought a 48V power supply for dirt cheap (around $20 or $25 with shipping).  Maybe the time of creating your own power supply from multiple PC power supplies is over.  That being said, I will not miss it.  Doing it that way requires a lot of extra wires which most of them are unused.)  The four PC power supplies take up the top 1/5 of the backbox.  The MaxPower board takes up a small amount of space just below them.

I was handed back a small form factor PC (mini-ITX based card) that was no longer wanted.  I had that sitting on the side running windows XP, but it was cumbersome to move that around with all its extra stuff.  I decided to rip that apart and also mount that stuff in the backbox.  That includes another PC power supply, the mini-ITX motherboard, and a hard disk drive.  All of that stuff will be removed and replaced with a single Raspberry Pi eventually.

I mounted a speaker panel which also allows the bottom half of the monitor to show through.  The top half of the monitor is going to be behind the backglass and will have a transparent window in the backglass so that I can display images.

I’m having troubles mounting the monitor, but I’m trying to spend a good amount of time to get it right, so that it can easily be removed for “servicing.”  That involves building a bracket of some sort out of metal.  I have the metal left over from the ground that was in the back of the backbox.  Plenty of metal, but I need to make clean 90 degree bends with a good degree of accuracy.  I don’t own a metal brake, so I’m being very cautious.  Here are a couple of pictures of backbox, and backbox without the monitor.


Last thing that I spent a good amount of time on these last few weeks is adding to the pinball framework or more specifically to the GenPyCode program.  That takes the rules.txt and generates Python files that are used by the pinball framework.  The generation of all the files except one is complete at this point.  For details look at the Subversion repository check-in.  Within the next week or two, I should have that completed and should be back to being able to start working on the actual rules of the machine.

I have not finished wiring the GI, and it is simply a couple hours of work that I need to do.  Since the lights were so dim, I didn’t feel like bothering, but now with the LED bulbs, I’m hoping to get back to that.  I need to start working on putting the playfield in the cabinet, but that is only after all the wiring is done.

It’s been a busy couple of weeks, but things are moving quickly.  It’s amazing how quickly two weeks goes by, and that deadline of the beginning of July is looming ever closer.

2 responses to “1/19/2015, Backboxes, Playfields and Screens, oh, my!

  1. honestly, 4 pc power supplies is ridiculous. Meanwell 48v, they are rock solid (weight like 10lbs!), chinese non name clones are not worth the money, and only weigh like 1lb. huge difference in quality!

    • I fully admit 4 PC power supplies is ridiculous. I knew that a manufacturer would be coming down the pipe with a better 48V supply that would be the right price point, but at the time, I couldn’t wait for it. With the PC power supplies, I tend to always buy named power supplies because I feel they will last longer, and tend to only be a buck or two more expensive.

      Cheaper power supplies tend to have poorer quality capacitors and inductors or lower values for those components. That being said, the quality at the low end of both of those components have gone up significantly in the last 20 years. The frequency of the switching components inside the power supplies have also increased dramatically which has meant lower inductance and capacitance will work.

      Pinball machines have really simple power needs. They require huge spikes in power, but it doesn’t really matter how clean the power is. If you are running your flippers at 60V and the power dips to 58V because the pop bumpers are also going, a player won’t really notice.

      A huge reservoir cap makes a lot of sense in a pinball machine to make sure it can provide the power spikes to kick the solenoids. The constant current draw is relatively small in a pinball machine. The biggest constant current draw is holding the flippers up, and that only takes about 1/20 or less of the current used for the initial kick. (based on cold coil resistance).

      When I get time (probably in August), I’m going to take some good measurements on exactly how much current the solenoids take. I’ve been wondering that for quite a few years now, and just can’t find a definitive source of information. Once you have that piece of information, sizing your power supply is trivial.

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