1/17/2021 – Cobra’s Kickstarter

Cobra18t on pinside has produced an “all in one” board for controlling pinball machines. OPP was originally envisioned as a distributed pinball controller to reduce wiring and such. Of course, many people have playfields out there that they don’t want to rewire. (When the Dolly Parton machine was converted to Van Halen, all of the controller cards were placed in the backbox so no wiring changes were needed on the playfield).

Many people have asked for a single card solution to control the whole pinball machine that would live in the backbox. Many people have also asked for a solution where they don’t need to solder their own cards. OPP was always meant to be the rock bottom cost-wise solution and people would need to add a little sweat to make it work.

Cobra18t has decided to take a different tact and produce an “all in one” card (the Cobrapin) that sits in the backbox. It has many surface mount components that make it more manufacturable. The project combines what is needed to drive a pinball machine into a single card and it is pre-assembled. It is essentially two STM32 processor cards with six solenoid wings, an 8×8 switch matrix, and two Neopixel wings. (Strangely, it is only now, after writing that sentence, that I remembered he asked me to support a Neopixel solenoid which converts one of the direct inputs into a Neopixel driver. That makes a lot of sense looking at his board). It also adds the bulk capacitors for the power supply filter board (and even a fuse!).

Cobra18t has already spent a lot of time testing the board and has done a really good job of making sure that the parts are robust enough to drive a pinball machine. (I believe he is on his third revision) If you search around, there is a video on his youtube site where he is driving all the solenoids very quickly and he measures the temperature rise to make sure it can handle the thermal load. Great stuff. He and Jan were also instrumental in testing the OPP Neopixel support, including the aggregation of fade commands. At this point, I feel the OPP Neopixel support is better than any other MPF supported Neopixel driver. Without their help and testing, the OPP firmware would not be as robust.

At this point, cobra18t is going to make his goal. (He is currently at $5800 with a goal of $1000). If you are looking for an inexpensive controller that doesn’t involve soldering a whole bunch of wing boards and programming the firmware, this might be a good option for you. Here is the Kickstarter link: https://www.kickstarter.com/projects/1862357036/cobrapin-pinball-controller

11/3/2020 – Loading STM32 Firmware

Well, for a long time, I’ve been referring people to a random YouTube video that tells them how to install firmware on a STM32. That seems both inadequate and relatively lazy on my part. I’ve been meaning to write down a little bit more detailed instructions, so here they are. The instructions assume using a ST-LINK V2 to program the stm32f103c8t6 blue pill board. So without further ado, here we go.

Linux (Ubuntu) Instructions:

Install required software:

  1. Install libusb and git: sudo apt-get install libusb-1.0-0-dev git
  2. Move to home: cd ~
  3. Grab stlink code: git clone https://github.com/texane/stlink
  4. Move into stlink folder: cd stlink
  5. Build stlink: make
  6. Copy binary to /usr/bin: sudo cp build/Release/bin/st-flash /usr/bin

Attaching the debugger and programming firmware:

  1. Connect the four pins at the edge of the stm32f103c8t6 to 3.3V, SWD, SWCLK and GND to the pins on the ST-LINK V2
  2. Move the Boot0 jumper from position 0 to 1
  3. Plug the ST-LINK V2 into a USB port
  4. Program firmware (firmware is found at repos/Stm32Workbench/Gen3Images): sudo st-flash –format ihex write OppStm32.
  5. After programming is completed (printing out Jolly Good!), unplug the ST-LINK V2 from the USB port
  6. Move the Boot0 jumper from position 1 to 0

Verify firmware version:

  1. Plug the stm32f103c8t6 into a USB port
  2. Run Gen2Test.py (Gen2Test is found at repos/Python/Gen2Test): sudo python Gen2Test.py -port=/dev/ttyACM0

Note: Gen2Test.py may need to be run a few times to “sync” the serial port because plugging in the USB port may send garbage on the serial port.

Windows Instructions:

Install required software:

  1. Download STSW-LINK004 from http://www.st.com: https://www.st.com/en/development-tools/stsw-link004.html
  2. Run setup.exe found in the zip file. This will install the STM32 ST-Link Utility

Attaching the debugger and programming firmware:

  1. Connect the four pins at the edge of the stm32f103c8t6 to 3.3V, SWD, SWCLK and GND to the pins on the ST-LINK V2
  2. Move the Boot0 jumper from position 0 to 1
  3. Plug the ST-LINK V2 into a USB port
  4. Run STM32 ST-Link Utility
    1. File->Open File and browse and select firmware file (firmware is found at repos/Stm32Workbench/Gen3Images)
    2. Target->Program and Verify
  5. After programming is completed, unplug the ST-LINK V2 from the USB port
  6. Move the Boot0 jumper from position 1 to 0

Verify firmware version:

  1. Plug the stm32f103c8t6 into a USB port
  2. Run Gen2Test.py (Gen2Test is found at repos/Python/Gen2Test): c:\Python27\python.exe Gen2Test.py -port=COM3

Note: Gen2Test.py may need to be run a few times to “sync” the serial port because plugging in the USB port may send garbage on the serial port.

Ending Comments:

That’s it. Hopefully these instructions are a little bit easier than doing a bunch of web searches and sussing out which instructions are applicable to your situation.

4/29/2020 – Fantastic new illustrations

So, as stated in my last blog entry, my photos stink.  I apologize for that, and since this is essentially a technical blog, I don’t go out of my way to make them any better than they happen to turn out.  (I don’t have a particularly nice camera, and much to the chagrin of my wife, really don’t care.)

I’m sure that anyone who is a graphic designer cringes at those images.  Luckily enough, somebody was so distraught by the photos that they decided rise to the occasion offer up some help.  My deepest thanks to Adrien A-G for providing these much clearer illustrations.


The first image shows the changes that need to be made to support all four wing boards fully.  The second image shows a Neopixel as wing 0 (all unused pins are configured as direct inputs), solenoid as wing 1, input as wing 2, and SM incandescent board as wing 3.  The last image shows a solenoid plank board being used in wing 2 and wing 3 positions.  As noted earlier, plank boards cannot be supported in wing 0 and wing 1 positions because of the USB bus pins that split the two wings.

The only final caution that I need to add is that the serial LEDs usually expect a 5V control signal level.  To work properly, I have found that I need to use a 3.3V to 5V converter on the PB15 pin so that the serial LEDs can be driven as brightly as possible, and the control of the LEDs work perfectly.

Thanks again, Adrien A-G.  I would like to say that I will try to make better illustrations, but let’s be serious, you can’t teach an old dog new tricks, and I’m just too darn old.

4/5/2019 – STM32 Firmware Complete

The STM32 firmware is now fully functional, tested and complete.  Special thanks to both Jan (for MPF support) and Cobra18t (for helping test).  Both helped immensely during the change from the PSOC4200 to the STM32.  The firmware is released at version

An added bonus is now MPF is able to use serial LEDs (Neopixels) driven by OPP, and in any configuration such as GRB, RGB, GRBW, RGBW.  This should be a much cheaper alternative than the FadeCandy option if you are trying to build your own low cost homebrew machine.  From my non-extensive research, the OPP serial LED support should require much less processing than running the open pixel server.  OPP supports over 230 LEDs per STM32 board.

The information on how to attach wing boards to the STM32 was scattered over multiple posts in forums, so I’m going to try and aggregate it here so I don’t have to keep searching for it when I need it.

These pictures are great examples why I should never be allowed to take pictures.  Look how blurry!  I guess nobody subscribes to this blog because of the desire to see the crispest pinball photos.  Hopefully they get the point across.  There is a lot of good information on these two pictures.  They show the positions of each of the wing boards with respect to the STM32F103C8T6.  Note in particular the two pins that are left blank between wing 0 and wing 1.  These two pins are used by the processor for USB communications.  This is why plank boards can not be used on the wing 0/wing 1 side of the processor.  The picture also shows that a wire must be added between PA13 and wing 0 pin 0 to fully support the wing 0 board.

Jumping to the back side, wing 2 requires the most aggressive modification.  The VB pin (battery voltage) has a trace that goes to the top right pin in this picture.  That trace must be cut.  When I cut traces, I make two separate cuts in the trace, then use an xacto knife to remove the copper trace between the two cuts.  That is very easy to do in this case, and it guarantees that the trace has been fully cut.  Last thing is to add a wire from PA14 (SWCLK) to the top right pin.  Now the wing 2 is fully supported.  The second picture shows the wing 0 modification from the bottom.  I chose to do that modification on the top of the board, because it was easier with my soldering skills.

One final note.  When using wing 2 and wing 3 as a switch matrix, wing 2 must be the switch matrix output (i.e. control signals to drive the switch matrix), and wing 3 must be the switch matrix inputs.  This is because of the LED (attached to PC13) which is populated on the board.

Keep your social distance by building your own personal pinball machine.  Keep safe!

1/12/2020 – Wayyy Too Lazy

Mostly my fault, but I just haven’t felt like writing anything on the blog lately.  Every once in a while, I think to myself that I really need to update the blog so people know things are occurring, but then I decide to go work on something else, and the blog is forgotten again for another month.

Here is the current status:  OPP firmware has been moved from the PSOC4200 to the STM32 and everything that MPF supports is supported by the new firmware.  Regression tests have been run, and so all past functionality has been verified including switch matrices.  (Those were the tall straw that ended up taking the longest because the newer processor is significantly faster and thus the capacitance of the inputs for a switch matrix needed a little help.)  All the new code is in the repository so version should be fully qualified.  Thanks for the big help from cobra18t for helping me test the switch matrix stuff.

After finishing that up at the beginning of January, I started talking to Jan about what is the best interface to support for MPF and Neopixels.   After a little bit of discussion, I feel that I have a small efficient interface that should work well with how MPF wants to send updates to a pixel controller.  That is work that is on-going, and even if I finish the firmware, it will still be a couple of weeks until the interface to MPF is finished.  (OPP PSOC4200 boards supported Neopixels, but I never wrote the interface necessary to make it work seemlessly with MPF.  I’m now making a concerted effort with the STM32 because I feel it has the bandwidth necessary to make that interface work well.)

The STM32 processor is cheaper than the PSOC4200 processor boards, and all of the wing boards work with the new processor without any modification to the wing boards.  (That was one of the main design goals).  The plank boards can only be used on the left side of the processor because the USB to serial port takes the center two pins on the right side.  Cobra18t has boards that can convert from a STM32 to the same form factor as the PSOC4200 so those small breakout boards could be used.  (Contact him on pinside if interested.)

Here are the two main threads in the MPF user group discussing the updates to OPP, testing, and where it is going next:



That’s all I have for tonight.  Just got the DMA running properly to update the NeoPixels, but haven’t verified the output yet to insure the pixels are being lit properly.  That will probably happen in the next few days.  Hopefully in the near future OPP can provide a cheaper way to use pixels without the expense of the current offerings.

9/6/2019 – Discussion on future of OPP

A discussion topic on the future of OPP and what the next steps are has been opened in the MPF User’s forum.  It was opened there because my guess is that the majority of the people using OPP to build pinball machines are also using MPF.  If interested in adding to the discussion, here is the link.  The discussion focuses on whether it makes sense to transfer the firmware onto the STM32F103 processor and continue to be a distributed solution, or would does it make more sense to create a more centralized solution.  All pertinent comments are welcome.

8/27/2019 – Oh no…the Fatal Flaw

Alas, there was one fatal flaw that could deal a harsh setback to the OPP project.  What could it be you may ask?  It is simply that the PSOC 4200 developer boards that OPP requires stop being manufactured.  As you probably know, OPP uses the CY8CKIT-049-42xx development board as the main processor.  Cypress, without notification, seems to have discontinued manufacturing the development board.  Let’s look at this quick link from Cypress that was updated on 6/26/2019, yet fails to mention that the boards are not going to be produced anymore.  Mouser lists the board as obsolete.  There are a couple available on Ebay, a couple available on AliExpress, but as of this moment, I can not find a “supplier”, i.e. a person that could sell ten of these on demand.

The most annoying part of this is that I was not notified by Mouser, Cypress, or the different distributor channels.  I get a few emails every year saying that this part has been changed, this part has a last time buy, etc.  There were absolutely no notifications received about the developer board going obsolete.  (It might be because Mouser only notes obsolescence with individual chips, and not developer boards, falsely assuming that projects are not using the whole developer board as part of a larger build.)

So first things first.  What if somebody gets caught out without having the PSOC cards that they need to create their dream pinball machine?  At this point I have six CY8CKIT-049-42xx in the stock room (i.e. my basement).  Contact me if you need a board and I will get it to you until my supplies run out.

Going forward, that won’t work, so what is next.  Somebody pointed out that I should look at the STM32F103 development boards that came out a couple years ago.  After a little bit of research, it seems that the boards are already being produced in China, and the Arduino code base has been ported by a few people.  Arduino only really matters to me because I feel it will guarantee that the board will be produced for a longer period of time.  I don’t want to be caught in the lurch again trying to move all of the firmware to yet another processor.  (That would be the third because OPP originally started on HCS08 based processors, then moved to PSOC 4200, and now it looks to move to STM32 based processor).

A quick look at the pinout of the stm32f103c8t6 board (hellishly known as the “blue pill”, don’t search on that), it seems that I can come up with a way to support the wing boards without any modifications.  There at least seventeen inputs/outputs on the left side, and fifteen inputs/outputs on the right side so I may need to describe moving a wire for an input from the left side to the right side.  (That is unless I can figure out a way to make the NRST a generic input/output pin which may be impossible).

There are some good points to the new processor.  The stm32f103 supports a USB virtual com port.  That will significantly increase the bandwidth for communications to the board.  It should remove the need to daisy chain boards, and a simple USB hub should suffice to talk to multiple cards.  While that increases wiring between the main processor and the individual controlling cards, it will make communication much simpler.  The processor itself is much faster, and has much more memory.  The USB stack will eat up a good portion of that extra memory, but on the balance, there should be plenty leftover for pinball.  Last change is that the outputs are only 3.3V as opposed to 5V.  Shouldn’t be a problem for solenoid control since the threshold voltage of all the MOSFETs are well below that level.  Switch matrices should work properly, but that would be what concerns me the most.

Two weeks ago, I bought a couple of the STM32F103 boards, and installed all the tools to start programming the boards.  I got three boards, and the ST-LINK V2 programmer for $11.49 from a guy out of Ohio.  It was a buck or two more than from AliExpress, but got here in about a week as opposed to a month or two.  The STM32F103 boards go for about $1.70 on AliExpress which is significantly less than the $4 price that the CY8CKIT-049-42xx used to be.  As I progress and move the OPP code over to the STM32F103, I will post updates.


12/30/2018 – Arduino, Knockout

I think this is my final Arduino entry.  I finished implementing and testing using two solenoid wing boards using an Arduino nano, and everything is working as it should.  I didn’t implement any of the serial communications mostly because I stopped understanding what I was gaining using the Arduino nano platform.

I chose the nano because of the price and it was approximately the same cost per pin as the PSOC 4200.  The PSOC is $4 an has 36 I/Os, and the Nano is about $2 and only has 16ish usable I/Os.  The PSOC is a much more powerful processor, so I was losing some performance there.

The one nice thing is that the Arduino has the super easy hardware abstraction layer (HAL) which makes it rather simple to program.  The problem was that every time that I used the HAL, the performance was atrocious because I didn’t like the decisions that were made to make it simple.  There are a ton of busy waits which makes programming easier, but it reduces the processor usefulness even further.  To get true real time performance I ended up bare metal programming the processor.  That meant that I really wasn’t using the Arduino platform at all, but I was just coding another inexpensive processor.

So then there are the pinout choices that the Arduino made.  It was very difficult to get a group of eight useful pins in a row which meant making very small wing cards work properly was a pain in the butt.  The Atmel choice to not make all of the analog inputs to be used as digital I/O further complicated the code.  (Atmel has said they will fix this in the next version of the chip).  While coding, I had to keep a map of the pins sitting beside me because the pinout was not logical.

All in all, I just don’t see what I was gaining.  That’s why I’m ending it.  The price difference was not sufficient to make it worth all the extra work.  The performance was significantly lower.  I enjoyed playing with the Arduinos, but at this point, I’m at been there, done that, stage.

11/17/2018 – Arduino, round 2

Well the Arduino nano performance was atrocious, but I blame that mostly on the Arduino framework itself.  After doing a little bit of research, it seems that reading the analog inputs occurs using a busy wait.  A read can take approximately 100us, so that means that most of the time is spent waiting for the ADC to complete its conversion.  That’s what I will target to make it more efficient.

So in my first rendition of the program, I read four analog inputs and four digital inputs for the inputs of the solenoids.  I could just as easily have read two analog inputs, and six digital inputs to minimize the number of analog reads.  The second program ArduinoBareOPP.ino uses the smaller amount of analog inputs to minimize those reads.

If the Arduino framework forces me to busy wait reading from the analog inputs, it is time to add an interrupt in.  The interrupt gets called after the ADC completes.  At that point, I set the mux to read from the next channel and kick that conversion off.  That means that the conversions are happening in the background without busy waiting for those to complete.  In the interrupt, I also fill currData which holds the value of the inputs.  This is also where I convert it from an ADC sample to a single digital bit using a threshold.

Lastly, I’ve heard that reading bits using digitalRead does a whole bunch of verifications on the inputs.  Why not just read directly from the Atmega328p register and do all the bits at once.  The code at the beginning of “loop” does the necessary bit manipulations to get this to happen using a single read from the PORTC and PORTB registers.  I haven’t converted the output bits to using direct register writes, but they happen so much less frequently, that it won’t make much difference.

So immediately after burning the code, I noticed that the LED which I use to time the loop is much less blinky.  (Before, I could notice a very faint flicker in the LED, but now it seems to be continuously lit dimly.)  That is a good sign.  The real test is when I throw it on the logic analyzer.  So now I get the main loop taking between 23.5 us and 29 us.  That is a significant improvement from the original 488 us.  (1/20th of the time).

So the pulses normally take 4 us, then every once in a while they take 11 us.  This probably means that the interrupt takes about 6.5 us or 7 us.  That also matches up nicely to the 6.5 us difference that I see in the length of time it takes to run the main loop.  It also says that I should take the time to stop using digitalWrite and write directly to the register.

Here is a link to the bare metal version of the code.

11/14/2018 – PSOC vs Arduino nano – Round 1

Finally…today I got my nano boards.  I ordered them on 9/30/2018, and, well 45 days later, I received them.  The main issue that I have is that the seller told me a week after I ordered them that I should expect them within a week.  Seems what he really meant to say is that it would take about another month or more to get them.  Water under the bridge as they say.  (You also get what you pay for, and 5 nanos for only $10.53 isn’t that bad I guess).

So, I soldered the headers on one of the boards, uploaded the program to the board (it uses the old bootloader), and suddenly the little test loop program that could fire solenoids was running.  It was relatively painless except for the fact that the Arduino IDE doesn’t like to program it twice in a row without closing out the program and restarting it.  (It seems to default to looking for the elf file in a location that doesn’t exist).

So I’ve set up the program to act like there are two solenoid wings attached to the board.  A solenoid wing has four inputs, and four MOSFETs for driving a solenoid, so in total there are eight solenoids being polled, and it is controlling eight outputs turning the MOSFETs on and off.  There is enough logic to drive the solenoids for certain period of time for an initial kick and to PWM a single coil flipper.  There is no serial controlling logic to allow a host computer to kick a solenoid, or even read the current state of the inputs from a “rules” computer.  That will come a little later.

At the end of the main loop, I pulse Pin13 (the one attached to the LED) high and then back low to give a quick pulse.  This is a really easy way to do timings to figure out how long it takes to execute the main loop.  After throwing the logic analyzer on Pin13, I got an initial measurement of 488 us.  Hmmm, that is pretty darn slow, especially since I am not doing a lot of the other processing that is necessary to allow a pinball system to work.  Let’s say that the initial pulse is set to 32 ms.  32 ms +/- 488 us has an error of over 1.5%.  I have not tried to “optimize” the program in any way.  There are many websites, that talk about ditching the Arduino framework and bare metal programming the processor.  That will be my next step.  It is an interesting first marker in the sand.

Let’s go over to the PSOC and see how fast it runs its main loop.  I instrumented it up so that bit 4.3 is gives a rising pulse each time the main loop is completed.  (Note:  These timings are with no serial traffic occurring, so there is almost no jitter in the signal).  The PSOC board is configured with the following 4 wings:  neo-pixel, input, solenoid and incandescent.  (The incandescent wing was chosen, because even when idling, it defaults to blinking the incandescent lights so in white wood mode, the lamps can easily be tested)  With that configuration, the main loop occurs every 84.5 us to 86 us, or about 11,500 per second.  The loop rate seems sufficiently high that the error should not affect the power of pop bumpers.  SS3 uses 32 ms for the pop bumpers/slingshots, so 32 ms +/- 86 us or an error of .3%.

As I get more time in the next couple of weeks, I’ll try to bare metal program the Arduino to see if I can get the rate much higher.  Here is a link to the Arduino nano program.