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.

11/3/2018 – Using incandescent wing as HiVolt inputs

Every once in a while, somebody starts emailing me about a technical question and after a couple of emails, a solution is created, and all the information disappears into the ether.  Maybe others could use this information, but I rarely take the time to put the solution out for others to benefit.  Well, since I’m still waiting for my Arduino nano boards, I will take this time to bring up one of those small projects.

A couple months ago a user wrote the following:  “Because of the half scale of my pin, the ball is too light to press a mechanical switch, I use in some instances IR detectors and induction (proximity sensor) switches but induction sensors are 12v (6v to 36v to be precise but I have a 12v psu already).  Is there a simple way to connect it to the processor board without damaging it?”  Originally he proposed using an opto-coupler board as a solution (approx $6.68 for 4 bits + $3 shipping), but suddenly my inherent cheapness caught the better of me.  Could I do it for a much lower cost?

So the basic issue is a 12v input needs to be attached to a processor pin which can only support up to 5v (in the case of the PSOC).  While using an opto-couple board would work wonderfully well, it is just a little too expensive in my opinion for what is needed.  Why not use an incandescent board flipped 180 degrees from how it is normally used?

Could a BS170 transistor make it work?  If the signal goes between 0 and 12V when the IR signal is blocked or not blocked, you could use that as the gate of the transistor.  The drain of the transistor is hooked to the processor input, and the source of the transistor is hooked to the ground of the processor.

Here is a link to the BS170 datasheet:  https://www.onsemi.com/pub/Collateral/BS170-D.PDF

The gate threshold in the On characteristics section of the datasheet says, anything on the gate < 0.8V (the minimum), the transistor is off, so the processor will read high since the input bits are pulled up to 5V internally.  If the gate voltage rises above 3V (the maximum), the transistor will turn on, and the input will be pulled to ground.  BS170 are about 12 cents each if you buy about 100.

The only issue that I can think of off the top of my head is that the sense of the input will be backwards.  Normally a closed switch is read as low.  If it is like an IR sensor, when the sensor is blocked it actually gives low voltage, so that would read high at the processor.  If the IR sensor is not blocked, it gives a high voltage so it would read low at the processor.  If using MPF (Mission Pinball Framework), the input bit can be configured as active high, so it should not be a problem.

On the incandescent wing, the connections that normally attach to the processor go to the gate signals of the BS170s and are attached to the output of the inductor sensor.   Attach the inputs from the processors to what is normally attached to the incandescent bulbs.  (Don’t populate the pullups).  At that point you have 8 of the circuits in a nice little package without having to proto board anything. The gate of a BS170 can handle up to 20V, so your induction sensor at 0-12V should be fine. The BS170 acts as a voltage translator, so that high voltage never touches the processor pins. You will have to tie the logic ground from the processor and the ground of the voltage source for the induction sensor together.

The induction sensor turns on and off the transistor. (turns on and off the switch). The source of the transistor is connected to logic ground. The drain of the transistor is connected to input of the processor. When the inductor sensor sends a high voltage, the transistor or switch closes, so the input is grounded. When the inductor sensor sends a low voltage, the transistor or switch opens, and so the input is floating, but there is an internal pullup resistor in the processor so it reads a high voltage.

Here is an attached picture that he sent me to be a little more clear:


In other news, I moved the firmware from to after re-running all the regression tests and adding a new test for the CAN_CANCEL.  That feature was added a couple weeks back so that the initial kick of a solenoid could be canceled so things like tap passing is supported by the OPP hardware.  (Thanks to Jan for adding the necessary code in MPF to make that happen on their side).