Progress 8/10/2014, Popping MOSFETS like Jiffy Pop Popcorn…and more.

[Week ago information that wasn’t posted]  Title pretty much says it all.  I got around to testing some of the MOSFETs that I was using with the flippers.  If the flippers are only around 1.2 ohms, and I throw 48V across them, it gives me about 40A of current (worst case, ignoring increases in resistance due to heat).  Needless to say, a 12A MOSFET doesn’t last very long at that point.

I tossed the flippers onto another channel on the solenoid driver (oops, it was one that I had set as a really strong kick), and of course popped another FET after about a minute of flipping.  I had already dropped the voltage down to 24V (since the power supply outputs it), but it was still a little bit too much current.  I had cheaped out on the FETs that I bought which is fine for all of the channels except for the flippers.  Those channels really need an IRL540N that can handle 26A continuously at 100C.  The funny part is that it would have worked on a newer pinball machine since the current is lower.  I may cobble something together so that I can keep moving, and I still have a good amount of wiring to do to get all the solenoids firing automatically.

Spent the time today to tighten up the rotisserie.  It is now much more stable, and an absolute pleasure.  I added foam beneath the playfield so that it couldn’t short to the rails.  The foam also raises the playfield enough so that the electrical components don’t touch the rail.

[New information]  Of course I wrote the previous stuff a week ago and never posted it.  Ordered the heftier FETs and got them in on Saturday.  Wired all of the ground connections to both the switches and the switches on the solenoids.  It took a couple hours but one of the kids helped me.  Eight year old children are able to cut wires to length, strip them, and do small amounts of soldering.  The nice part was that it only left about 30 minutes of wiring for today to get all of the solenoids working.  That happened before the end of the night, flipped the pinball machine around on the rotisserie, and there was a functional pinball machine.  Right before bed the kid tossed around the ball to fire all the solenoids.  There might have been an aha moment realizing that the wiring work brought the machine back from the dead.

So what do I have right now?  A powered pinball machine that the playfield layout can be tested.  The solenoids drivers are configured to drive the solenoids properly so no coding is necessary to get that to happen.  The goal of being able to test the layout without needing to program the machine has been achieved.  There are no rules, no switches that don’t attach to a solenoid, and no feature lights.  I have two GI light bulbs wired, which is used to tell if the machine is on/off.  Right now the drop targets aren’t working because I need to fix the broken targets, and wire those switches.  When the game is finished, the main processor will reset the drop targets, but right now, I have a separate switch to do it.  I still need to wire all the normal switches.  The feature lights I’m building another board so I can support the incandescent bulbs.  That is probably the long lead item at this point since it takes about 4 weeks to get the cards.

Video.  Yeah, words are great, but a video is the only proof that it is actually working.  I will probably try and get something together Monday night.   The flipper buttons are just hanging in mid-air at this point, so I need something a little better for them.

I also want to do some measurements on currents drawn etc.  I can’t find any truly good resources on the web about what the current curves should look like for flippers, pop bumpers, etc.  There are a couple sites which list resistances, but I don’t know the inductance.  I soldered up a current sense resistor, and I have a oscilloscope, so I should be able to get the information relatively easily and post it.

4 responses to “Progress 8/10/2014, Popping MOSFETS like Jiffy Pop Popcorn…and more.

  1. Hey man, nice work. Keep the updates coming! Do you have your circuit diagrams posted anywhere?

    • The circuit diagrams are all in the Google code repository. The circuits are done using Kicad which is open source and doesn’t have restrictions like Eagle. I haven’t gone through the trouble of converting the schematics to PDFs but it is really simple to pull the repository and open the files up in Kicad. The *.sch file are the actual schematics, while the *.pcb files are the PCB layouts. *.pro are the project files which allow you to open up either the schematics or layouts in their control panel. You may need to include the Libraries subdirectory in the Kicad search path to find any project specific parts.

  2. Ahh I found them! I couldn’t find a link to the repo anywhere after some quick searches. Thanks.

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