1/19/2017 – PwrFilter/Bally Intf boards received

Yesterday the boards came in from ITeadStudio.  Their newest cheap shipping option (SF E-Parcel) is really fast.  So I ordered the boards on 1/5/2017 (yeah, it was late Thursday night).  They shipped the boards on 1/12/2017.  I received the boards on 1/18/2017.  That’s about a two week turn including shipping which is really fast.  The shipping was only about $14 for two sets (10 boards) of 10cm x 10cm boards.  Nice!  Unfortunately my cheap 36V SMPS power supply hasn’t arrived yet, but as soon as that gets here, I can do some quick testing on the power filter board.  It is such a simple board that it should only take a day to verify it is working properly.

I built up a filter board tonight and took a couple pictures.  I’m happy after visually inspecting the boards, and look forward to getting the power supply to test even further.  This should clean up the back box of SS3 and make it quieter (the 4 cheap PC power supplies that I used have very loud fans.  It doesn’t matter when the glass is in the backbox, but when debugging, the fan noise is bothersome.)  I must also say, that I’m really sick of listening to the theme song to “The Good, The Bad and The Ugly”.  When playing, a game, it plays continuously on a loop.  I think that I could sing it in my sleep at this point.

The power filter board can be used to add bulk cap to 2 voltages or to 1 voltage.  (plated through holes are provided to tie the two planes together if the board is only used for a single voltage which is the configuration that I built up).  In that case, you only need one NTC thermistor, and one PChannel FET.  In the two voltage situation, you need two of those parts.  The board should insure that the SMPS will not incorrectly detect a spike when flippers are activated.


Populated power filter board. Shows input connector and NTC thermistor.


Populated power filter board. Shows filtered output connector and interface connector.

The bottom 6 pin connector contains 3 pins for each of the voltage sections.  For each section, one pin is ground, and the other pin enables the PChannel FET if it is grounded.  That can be controlled by a processor, or if you want to always have the voltage on, you can just use a 100 mil jumper between the ground pin and the PChannel FET.  If you want it to act like a normal pinball machine, you can add a normally closed switch on the cabinet door, and when the door is opened it breaks the connection and disables the high power voltage.  The last pin provides a digital output that can be read by a processor to check if the voltage is enabled.  (Just a simple voltage divider to provide the appropriate voltage for your processor).  That allows a message to be printed on an LCD screen or whatever.  Hey, the board even has two indicator LEDs to indicate that the voltage is hot.

I also now have all the parts for the Dolly retheme.  It is going to take a couple days for me to build up the OPP boards, but since I just received the Bally interface boards, nothing is stopping me from starting on that machine.  I’m currently moving faster on that machine than I was expecting.  Below is the blurriest picture ever to be added as part of a blog.  (Sorry).  I didn’t realize it was so blurry until after I took it off the camera, and I was too lazy to take another picture.


Bally interface board to OPP board

The large slashes through the connectors done in silkscreen note the pins on the connectors that are keyed.  That should make it easier to plug and unplug connectors because you can scan the key in the connector and line it right up.  That board hasn’t been populated yet.

01/14/2017 – New video of SS3 game play

Just a quick note that a new video was posted on the youtube channel.  SS3 is now playable.  Yes!  I’ll continue to work on it for the next few months so that it is much more polished than the last time that it was seen at Pintastic 2015.

Besides that, just received the parts for populating the filter power boards, and for redoing the Dolly machine.  I received a note from ITeadStudio that my boards shipped, so I should receive those in the next one or two weeks.  The new single power supply has been ordered to make SS3 run on a 36V SMPS and a single PC power supply instead of the 5 PC power supplies that it currently runs on.

Have a great weekend.

1/5/2017 – Filter and Bally Intf PCBs ordered

So the Power Supply filter boards, and Bally Interface boards got ordered today.  I was holding off on the order to save a little bit of money on the shipping from IteadStudio.  (Hey, a buck is a buck, right?)  I wanted to get them out this week, because Chinese New Year starts on 1/22/2016 and that closes the factories down for about 2 weeks.  By ordering this week it should give them plenty of time to ship the boards before that holiday hits.

So what the heck is the Bally Interface board alluded too by the title?  As you may recall, I have a Dolly Parton machine that I’ve been meaning to do a retheme.  The MPU board in it has massive amounts of acid damage, so that needs to be replaced.  (I actually bought a replacement board in Allentown about 5 years ago, but never bothered installing it.)  In the end, if I simply replace the MPU, I will have a working Dolly Parton with a completely destroyed playfield, and a backglass that is falling apart.  Sounds like a perfect machine to do a retheme so I can sand the playfield down to bare wood, replace the backglass with an LCD, and add some more rules to give a little more depth to the game.

Problem is that I don’t want to rewire the machine.  I had it up and running a bunch of years ago, and it was working at that point.  It booted and played, two of the five displays worked, etc.  Replacing the two displays would cost about as much as just throwing in an LCD monitor, so that is a no brainer.  Adding new rules requires a new MPU, so I might as well update it to use OPP boards to drive the machine.  That requires converting from the backbox boards in the cabinet to OPP boards.

The backbox of Dolly Parton has a transformer board.  (I’m not going to change anything on that board, and use it as is).  Then there is a lamp driver which was a simple low side driver for the lamps.  (I was actually expecting it to be a lamp matrix, but it turns out there is a wire for each controlled lamp).  Those two connectors will go to the interface board, and I will use six incandescent wing boards to give me the same functionality.  Next up are the two switch matrices (one for the cabinet and one for the playfield).  I was very surprised there were actually two separate switch matrices, but each his own.  For that, I’m going to add switch matrix support to the OPP firmware, so that will take up another four wing positions.  (The firmware will support up to 8×8 switch matrices.)  In Dolly, the cabinet is a 2×8 matrix, and the playfield is a 5×8 switch matrix.  Next is the solenoid driver board.   The board supports 20 solenoids, but the flippers are simply enabled using a relay.  The Bally interface board will support enabling and disabling flippers instead of grounding the flippers through the flipper buttons.  While Dolly only uses about 12 of the solenoids, I added the extra connectors, so the board could be used for other Bally machines with more solenoids such as Xenon.  The solenoid board also creates the regulated 12V and 5V for the processor.  Instead of generating those, I’m going to use a PC power supply.  A connector was added so the P4 motherboard connector could be plugged into the Bally interface board to tie the grounds of the PC power supply and the old transformer together.  I will end up adding a Raspberry Pi to drive the LCD monitor, and that should be all I need.

Here is a quick view of the PCB layout.  It was a pain to go through the old Bally schematics, but I needed to understand how all that of it was connected together to minimize the chances of needing to rewire stuff.  The schematics are very understandable after you figure out the notations that they were using at the time.  Some things were not as clear as I hoped, but on the whole, they were very good schematics.


Bally Interface Board

So since this is the first post of the new year, we can talk about numbers from last year.  We were pretty close to hitting 10,000 page views for last year, but alas, we fell 100 hits short.  In the end, there were 9,900 views.  Pretty amazing to me.  I could have added another post right before the end of the year, but that just seemed to me that I was trying to gin up the numbers.  There is really no point to that.

That being said, I’m pretty sure this is going to be the last major year for the OPP blog.  I’m running out of things to discuss, and if I get everything done that I’m planning, there really won’t be any other hardware that needs to be done.  I’ll still be around, but I doubt if I will keep updating the blog as frequently.  As I come up with pinball related stuff, I will blog about it, but beyond that it is going to slow down significantly.  But this year, 2017, the blog entries will come fast and furious.

That’s all for now.


12/25/2016 – New board announced

Open Pinball Project (OPP) Announces the Release of the critically acclaimed Power Supply Filter Board
For immediate release:

Westford, MA, Dec 25,2016 /PRNewswire/ — Open Pinball Project, the world’s least expensive provider for DIY pinball controllers, proudly announces the Power Supply Filter Board (Part#1018).  It features three huge capacitors for getting the biggest bang out of your cheap 48V switched mode power supplies (SMPS) bought directly from Ebay.  The bulk capacitors can be split into two separate voltages, or can be combined as a single voltage with 24.6mF of capacitance.  (That’s a lot of Farads!)

To reduce in-rush current, two NTC Thermistors can be populated.  The board features the ability to enable/disable the power supplies, processor feedback on the supply status, and high voltage active LEDs to make sure know when there’s danger.

As always, parts must be purchased separately, and assembly is required.

“This card has everything I could ever want” – Hugh (long time OPP supporter)


“I bought a competitor’s board at 5 times the price, and yeah, it was great, but really, 5 times more expensive.  Are they trying to get blood from a stone?” -anonymous

All kidding aside, the board is designed and laid out.  The schematic/PCB can be found in the repository.  I’ll send out for the boards in a week or two, and after testing, they will be available at Mezel Mods for $5.  There are about $15 in parts to populate the board in the most expensive configuration, so for about $20, you can really get the best use out of those 48V power supplies on Ebay.  Should be a lot easier than trying to create a proto-board to do the same thing.

Here is a quick PCB screen capture:


PCB layout for power filter boad

To receive the board and test it will probably take about a month or a little more since I’m designing another card right now, and want to save on the shipping.  Why do the NTC Thermistors go off the board?  That little bit of space savings allows me to get two boards in each 10cm x 10cm PCB.  That is a significant amount of savings.

Merry Christmas everyone and I hope that all their pinball creating dreams become reality next year.


12/4/2016 – New video on playfield wiring

As is evidenced, I can barely keep track of one blog.  Well, on Sunday I tossed up a new video on the Youtube channel.  I forgot to mention it here, so people who follow the blog but don’t follow the youtube channel might not have noticed it.  Sorry.

11/18/2016 – Stencils for Surface Mount Incandescent Wings

If you have ever populated surface mount boards by hand, you know that a stencil for spreading the solder paste is invaluable.  Before the Kickstarter, I tried to do it by just spreading the solder paste on using a dental pick, but I would get too much in some areas and not enough in other areas.  This would mean that I would have to go back through and use solder wick to clean up the extra lead.  It also meant that I would have to rework 2 or 3 pins per incandescent wing board.  Identifying issues and fixing them took a long time.

During the Kickstarter, I knew that I was going to need to build up about 30 of the incandescent surface mount boards for the big spenders.  Building them up using the through hole cards would take a long time to clip all of the leads and solder all those pins.  (The incandescent wing has the most solder connections on it.)  I ended up getting a stencil from OSH Stencils because they were the cheapest.  I dropped the Gerbers for the stencil in the repository so other people could order one if they needed it, assuming nobody would ever need one.

A couple weeks ago, the Mezels said they sold out of the incandescent surface mount boards.  I was surprised.  I reached out to OSH Stencils to see if there was a way to make the stencils available using a link so people don’t need to upload the Gerber files to order them.  Luckily the guy had just added that feature to the website.

If you are populating a surface mount incandescent wing board as a low side switch (i.e. enable and disable the ground connection to turn on and off the bulb), use this link:  Low Side Incandescent Wing Stencil.

If you are populating a surface mount incandescent wing board as a high side switch (i.e. enable and disable the power connection to turn on and off the bulb), use this link:  High Side Incandescent Wing Stencil.

If I needed to build 8 or 10 boards, a stencil would definitely make sense.  Less than that, I would probably just muddle through it and not get the stencil.  It is really based on what your time is worth.  The other nice part of the stencil is because you always get the right amount of solder paste, my yield rate jumped to 100%.  (i.e. I never had to rework any of the boards)  That made testing that much faster and more convenient because I could run through and test all 30 of the boards without needing to stop and fix issues that I found.


11/15/21 – Why is it so hard to explain grounding?

I think that the most common question that I ask people when I’m trying to help them out (after all the initial questions), is, “Are your grounds correct?”  It’s really important to get your grounds correct.  If the grounds aren’t correct, all sorts of issues will occur that will be nearly impossible to figure out.  The other issue is that trying to figure out grounding moves you from the realm of hobbyist to something a little bit deeper.  The nice part is that there are some rules of thumb that you can use to greatly simplify the issues that you will run into.  Hopefully laying out the rules of thumb will make it more understandable.  (Note:  This will not make you an expert on grounding, but it will hopefully give you some pointers.)

Rules of thumb:

  1. All current sourced by a power supply should return to that power supply.  (Don’t mix electrons up).
  2. All grounds should be connected together as close to the power supplies as possible.
  3. Big loops of wire, (especially with lots of current going through them) are bad.
  4. Bundles of wire containing both high current wires and signal wires are bad.

That’s it.  That’s all you have to worry about.  If you keep those simple things in mind, you will be fine.  Let’s dive into each of the rules and see what I’m trying to say about them.

All current sourced by a power supply should return to that power supply

OK.  Let’s talk about SharpeShooter3 (SS3) since it has five PC power supplies in it.  When I’m debugging, it actually has six power supplies in it, but we’ll ignore that.)

Four of the power supplies are connected in series to give me 48V.  Since each PC power supply only creates 0-12V, I basically connected the 12V of the first power supply to ground of the second power supply, etc.  To make that work, you need to disconnect the earth ground pin on the second, third and fourth power supplies.  If the earth ground isn’t disconnected, the power supplies will smoke.  (I think there is another connection that needs to be severed, but I can’t remember at this point).  If interested in that, read the old posts on the MaxPower card that I did.

So let’s assume for this discussion that those four power supplies form a single 48V power supply.  (Unfortunately, cheap 48V power supplies weren’t available when I made the MaxPower board.)   The 48V drives most of the coils in the pinball machine.  So that power supply has 48V and ground on the DC side.  (I’ll call that ground, gnd(48v) for this discussion).   So when I fire a coil, all of the current goes through the coil, through the MOSFET (which turns the coil on and off) and ends up at gnd(48v).

Now the next power supply, powers the computer and all the Gen2 boards.  The computer running the rules uses gnd, 3.3V, 5V, 5VSB and 12V.  The Gen2 boards use 5VSB and gnd from that same power supply.  (5VSB is the standby voltage that a PC power supply has.  It is always on even if the power supply’s higher voltages are turned off).  Let’s name that ground, gnd(5vsb) for this discussion.  Again, all of the current from that power supply needs to be returned to it.  Since the Gen2 boards are detecting when switches are closed, the switches must be attached to gnd(5vsb).  The inputs of the processor are internally pulled up to 5VSB.  When grounding the pin to indicate that the switch is closed, it must be attached to gnd(5vsb) because the current came from the processor’s power supply.

All grounds should be connected together as close to the power supplies as possible

So we have two power supplies with two different grounds (gnd(48v) and gnd(5vsb)).  You may wonder why we can’t just keep them completely separated.  That would work except for the MOSFETs which are where it starts to get interesting.  The Gen2 boards fire the solenoids.  To get a n-channel MOSFET to turn on and fire a solenoid, the gate of the MOSFET needs to be brought to about 3V above the source pin of the MOSFET (which is connected to gnd(48v)).  Since these are two completely separate power supplies, gnd(48v) may not be the same voltage as gnd(5vsb).

What you say?  But they are both ground.  How the heck can they be different voltages.  Just trust me…they can be because of how most switching power supplies work.

To get the MOSFETs to fire, we need to tie those grounds together.  Instead of connecting them near the MOSFETs, the best place is back near the power supplies.  In my case I have all the power supplies in the backbox.  The ground connection occurs in the backbox.  It doesn’t occur under the playfield where the MOSFETs are.  The reason for that is, if it was connected near the MOSFETs, some of the current from the 48V power supply may accidentally get mixed up and go to the 5VSB power supply.  Remember the first rule.  Don’t let current from one power supply get confused and go to the ground of the other power supply.

People have been known to add a 2 or 3 ohm resistor between the grounds to make sure that the current doesn’t get confused.  Yeah, that would work, but isn’t really necessary if you tie the power supply grounds together near the power supplies.

Big loops of wire, (especially with lots of current going through them) are bad

The only time that you really need to be conscientious of loops of wire is if it is carrying solenoid current.  Solenoid current can easily reach 5 or 10A which means it is really important to pay attention to loops.  Loops of wire with current running through it creates a magnetic field and can be affected by magnetic fields.  (That is how a solenoid works).  While a solenoid has many hundreds of turns to increase the magnetic field, even a single loop is bad.  Minimizing the size of loops is always better.

Do not do the following:  Do not run the 48V power line to power the solenoids down the left side of the bottom of the playfield, and run the gnd(48v) on the right side of the playfield to return the current.  Running the wires in this way, it would form an immense loop which is really bad.  (It also means that the loop of wire acts as an antenna which is a double whammy).

In a perfect world, I would run the solenoid power and grounds (48V and gnd(48v)) on the bottom of the left side of the playfield, and run little branches to each solenoid across the bottom of the playfield as necessary.  I would cable tie the 48V and gnd(48v) together because inducing noise between those signals doesn’t matter, so that would make the wiring that much cleaner.  Then I would run all of the logic voltages (5VSB and gnd(5vsb)) on the right side of the bottom of the playfield to keep them as far away from each other as possible.

The problem is the world is not perfect, so I didn’t really follow this rule 100%.  I tried to keep the 48V and gnd(48v) as far from the switch signals as possible.  Of course, if you have a pop bumper, by definition, there is a switch in close proximity to the solenoid.  Don’t worry about it.  It’ll probably be fine as long as you don’t cable tie those signals in a bundle and have the wires parallel to each other for 10 or 12 inches.

Bundles of wire containing both high current wires and signal wires are bad

This brings me to another point.  Impulses of current are also bad.  Going from 0A to 10A in a very short time induces voltage in wires that are run in parallel.  This is why I cable tie 48V and gnd(48v) together, but never cable tie those wires with a switch return.  The amount of induced voltage depends on the length of the wire where the signals are running in parallel, the square of the distance between the wires, and the speed of the change in current.  You can’t change the speed of the change in current (well you could, but then your flippers and pop bumpers would be weak, so that really isn’t an option).  You can minimize the length of wire that is parallel (i.e. don’t have gnd(48v) and logic inputs in the same bundle).  You can also try to make sure that those wires are as far from each other as is practical.  They will be close in many cases, but as long as they aren’t running in the same bundle, you will probably be fine.

So in my case Gen2 cards are distributed and so the longest lengths of wire that I really have under the playfield for inputs is 5 or 6 inches at the most.  If I have a 7 bank drop target, I put all of the inputs for detecting the drops are down in the same bundle because it makes things clean and tidy, and none of those wires are carrying much current, so they aren’t going to induce voltage in any other wires.

My ribbon cables for communicating between cards runs down the middle of the playfield.  That gives me some distance between the solenoid wires (48V and gnd(48v)) which are on the left side and the critical processor communication signals.  I’ve even broken this rule when going around the drop bank because it was a shorter ribbon cable to go near the solenoid wires that reset the drop bank target.

So I haven’t mentioned the lights and how they are powered.  Currently they are powered using 5V from the processor power supply.  (This is the high current 5V supply on a PC power supply)  I separate this voltage and ground from my 5VSB and gnd(5vsb) to make sure that the processors don’t get affected by the lights turning on and off.  That means that I have a third ground for lights that is gnd(5v).  That is probably not strictly necessary.  Since I am using LED bulbs, each bulb turning on and off really doesn’t create that much of an impulse in current.  Of each bulb takes 50 mA, so it would take 20 bulbs lighting up all at once to get an impulse of 1A.  Not nearly as much of a worry as the solenoids.  If I was really serious, I would run all those wires near the solenoid wires.  Ehhh, more than likely it doesn’t matter, and since the bulbs are distributed evenly around the playfield, I actually ran the 5V power down both the left and right side of the playfield.  That just made wiring easier for me.

That’s it.  Those are my rules of thumb when wiring a playfield.  If you follow them, you should have pretty good luck.  If interested, read up on the difference between a MOSFET and a Darlington transistor.  Old pinball machines used Darlington’s while most people are using MOSFETs in their homebrew pinball machines today.  Darlington’s back in the day couldn’t be driven directly from a processor because the amount of current through the Darlington is directly proportional to the amount of current put into the base.  This means that a second driver is needed to supply that current.  Glad we don’t have to do that anymore.  (If you have worked on pinball machines long enough, you have probably seen the big 10 ohm resistors that are limiting the current to the base of the transistor, and you have probably found a couple of them laying at the bottom of the back box because they got so hot they desoldered themselves.  Ahh, the good old days.)