An I/O controller for virtual pinball machines: accelerometer nudge sensing, analog plunger input, button input encoding, LedWiz compatible output controls, and more.

Dependencies:   mbed FastIO FastPWM USBDevice

Fork of Pinscape_Controller by Mike R


This is Version 2 of the Pinscape Controller, an I/O controller for virtual pinball machines. (You can find the old version 1 software here.) Pinscape is software for the KL25Z that turns the board into a full-featured I/O controller for virtual pinball, with support for accelerometer-based nudging, a real plunger, button inputs, and feedback device control.

In case you haven't heard of the concept before, a "virtual pinball machine" is basically a video pinball simulator that's built into a real pinball machine body. A TV monitor goes in place of the pinball playfield, and a second TV goes in the backbox to serve as the "backglass" display. A third smaller monitor can serve as the "DMD" (the Dot Matrix Display used for scoring on newer machines), or you can even install a real pinball plasma DMD. A computer is hidden inside the cabinet, running pinball emulation software that displays a life-sized playfield on the main TV. The cabinet has all of the usual buttons, too, so it not only looks like the real thing, but plays like it too. That's a picture of my own machine to the right. On the outside, it's built exactly like a real arcade pinball machine, with the same overall dimensions and all of the standard pinball cabinet hardware.

A few small companies build and sell complete, finished virtual pinball machines, but I think it's more fun as a DIY project. If you have some basic wood-working skills and know your way around PCs, you can build one from scratch. The computer part is just an ordinary Windows PC, and all of the pinball emulation can be built out of free, open-source software. In that spirit, the Pinscape Controller is an open-source software/hardware project that offers a no-compromises, all-in-one control center for all of the unique input/output needs of a virtual pinball cabinet. If you've been thinking about building one of these, but you're not sure how to connect a plunger, flipper buttons, lights, nudge sensor, and whatever else you can think of, this project might be just what you're looking for.

You can find much more information about DIY Pin Cab building in general in the Virtual Cabinet Forum on Also visit my Pinscape Resources page for more about this project and other virtual pinball projects I'm working on.


  • Pinscape Release Builds: This page has download links for all of the Pinscape software. To get started, install and run the Pinscape Config Tool on your Windows computer. It will lead you through the steps for installing the Pinscape firmware on the KL25Z.
  • Config Tool Source Code. The complete C# source code for the config tool. You don't need this to run the tool, but it's available if you want to customize anything or see how it works inside.


The new Version 2 Build Guide is now complete! This new version aims to be a complete guide to building a virtual pinball machine, including not only the Pinscape elements but all of the basics, from sourcing parts to building all of the hardware.

You can also refer to the original Hardware Build Guide (PDF), but that's out of date now, since it refers to the old version 1 software, which was rather different (especially when it comes to configuration).

System Requirements

The new Config Tool requires a fairly up-to-date Microsoft .NET installation. If you use Windows Update to keep your system current, you should be fine. A modern version of Internet Explorer (IE) is required, even if you don't use it as your main browser, because the Config Tool uses some system components that Microsoft packages into the IE install set. I test with IE11, so that's known to work. IE8 doesn't work. IE9 and 10 are unknown at this point.

The Windows requirements are only for the config tool. The firmware doesn't care about anything on the Windows side, so if you can make do without the config tool, you can use almost any Windows setup.

Main Features

Plunger: The Pinscape Controller started out as a "mechanical plunger" controller: a device for attaching a real pinball plunger to the video game software so that you could launch the ball the natural way. This is still, of course, a central feature of the project. The software supports several types of sensors: a high-resolution optical sensor (which works by essentially taking pictures of the plunger as it moves); a slide potentiometer (which determines the position via the changing electrical resistance in the pot); a quadrature sensor (which counts bars printed on a special guide rail that it moves along); and an IR distance sensor (which determines the position by sending pulses of light at the plunger and measuring the round-trip travel time). The Build Guide explains how to set up each type of sensor.

Nudging: The KL25Z (the little microcontroller that the software runs on) has a built-in accelerometer. The Pinscape software uses it to sense when you nudge the cabinet, and feeds the acceleration data to the pinball software on the PC. This turns physical nudges into virtual English on the ball. The accelerometer is quite sensitive and accurate, so we can measure the difference between little bumps and hard shoves, and everything in between. The result is natural and immersive.

Buttons: You can wire real pinball buttons to the KL25Z, and the software will translate the buttons into PC input. You have the option to map each button to a keyboard key or joystick button. You can wire up your flipper buttons, Magna Save buttons, Start button, coin slots, operator buttons, and whatever else you need.

Feedback devices: You can also attach "feedback devices" to the KL25Z. Feedback devices are things that create tactile, sound, and lighting effects in sync with the game action. The most popular PC pinball emulators know how to address a wide variety of these devices, and know how to match them to on-screen action in each virtual table. You just need an I/O controller that translates commands from the PC into electrical signals that turn the devices on and off. The Pinscape Controller can do that for you.

Expansion Boards

There are two main ways to run the Pinscape Controller: standalone, or using the "expansion boards".

In the basic standalone setup, you just need the KL25Z, plus whatever buttons, sensors, and feedback devices you want to attach to it. This mode lets you take advantage of everything the software can do, but for some features, you'll have to build some ad hoc external circuitry to interface external devices with the KL25Z. The Build Guide has detailed plans for exactly what you need to build.

The other option is the Pinscape Expansion Boards. The expansion boards are a companion project, which is also totally free and open-source, that provides Printed Circuit Board (PCB) layouts that are designed specifically to work with the Pinscape software. The PCB designs are in the widely used EAGLE format, which many PCB manufacturers can turn directly into physical boards for you. The expansion boards organize all of the external connections more neatly than on the standalone KL25Z, and they add all of the interface circuitry needed for all of the advanced software functions. The big thing they bring to the table is lots of high-power outputs. The boards provide a modular system that lets you add boards to add more outputs. If you opt for the basic core setup, you'll have enough outputs for all of the toys in a really well-equipped cabinet. If your ambitions go beyond merely well-equipped and run to the ridiculously extravagant, just add an extra board or two. The modular design also means that you can add to the system over time.

Expansion Board project page

Update notes

If you have a Pinscape V1 setup already installed, you should be able to switch to the new version pretty seamlessly. There are just a couple of things to be aware of.

First, the "configuration" procedure is completely different in the new version. Way better and way easier, but it's not what you're used to from V1. In V1, you had to edit the project source code and compile your own custom version of the program. No more! With V2, you simply install the standard, pre-compiled .bin file, and select options using the Pinscape Config Tool on Windows.

Second, if you're using the TSL1410R optical sensor for your plunger, there's a chance you'll need to boost your light source's brightness a little bit. The "shutter speed" is faster in this version, which means that it doesn't spend as much time collecting light per frame as before. The software actually does "auto exposure" adaptation on every frame, so the increased shutter speed really shouldn't bother it, but it does require a certain minimum level of contrast, which requires a certain minimal level of lighting. Check the plunger viewer in the setup tool if you have any problems; if the image looks totally dark, try increasing the light level to see if that helps.

New Features

V2 has numerous new features. Here are some of the highlights...

Dynamic configuration: as explained above, configuration is now handled through the Config Tool on Windows. It's no longer necessary to edit the source code or compile your own modified binary.

Improved plunger sensing: the software now reads the TSL1410R optical sensor about 15x faster than it did before. This allows reading the sensor at full resolution (400dpi), about 400 times per second. The faster frame rate makes a big difference in how accurately we can read the plunger position during the fast motion of a release, which allows for more precise position sensing and faster response. The differences aren't dramatic, since the sensing was already pretty good even with the slower V1 scan rate, but you might notice a little better precision in tricky skill shots.

Keyboard keys: button inputs can now be mapped to keyboard keys. The joystick button option is still available as well, of course. Keyboard keys have the advantage of being closer to universal for PC pinball software: some pinball software can be set up to take joystick input, but nearly all PC pinball emulators can take keyboard input, and nearly all of them use the same key mappings.

Local shift button: one physical button can be designed as the local shift button. This works like a Shift button on a keyboard, but with cabinet buttons. It allows each physical button on the cabinet to have two PC keys assigned, one normal and one shifted. Hold down the local shift button, then press another key, and the other key's shifted key mapping is sent to the PC. The shift button can have a regular key mapping of its own as well, so it can do double duty. The shift feature lets you access more functions without cluttering your cabinet with extra buttons. It's especially nice for less frequently used functions like adjusting the volume or activating night mode.

Night mode: the output controller has a new "night mode" option, which lets you turn off all of your noisy devices with a single button, switch, or PC command. You can designate individual ports as noisy or not. Night mode only disables the noisemakers, so you still get the benefit of your flashers, button lights, and other quiet devices. This lets you play late into the night without disturbing your housemates or neighbors.

Gamma correction: you can designate individual output ports for gamma correction. This adjusts the intensity level of an output to make it match the way the human eye perceives brightness, so that fades and color mixes look more natural in lighting devices. You can apply this to individual ports, so that it only affects ports that actually have lights of some kind attached.

IR Remote Control: the controller software can transmit and/or receive IR remote control commands if you attach appropriate parts (an IR LED to send, an IR sensor chip to receive). This can be used to turn on your TV(s) when the system powers on, if they don't turn on automatically, and for any other functions you can think of requiring IR send/receive capabilities. You can assign IR commands to cabinet buttons, so that pressing a button on your cabinet sends a remote control command from the attached IR LED, and you can have the controller generate virtual key presses on your PC in response to received IR commands. If you have the IR sensor attached, the system can use it to learn commands from your existing remotes.

Yet more USB fixes: I've been gradually finding and fixing USB bugs in the mbed library for months now. This version has all of the fixes of the last couple of releases, of course, plus some new ones. It also has a new "last resort" feature, since there always seems to be "just one more" USB bug. The last resort is that you can tell the device to automatically reboot itself if it loses the USB connection and can't restore it within a given time limit.

More Downloads

  • Custom VP builds: I created modified versions of Visual Pinball 9.9 and Physmod5 that you might want to use in combination with this controller. The modified versions have special handling for plunger calibration specific to the Pinscape Controller, as well as some enhancements to the nudge physics. If you're not using the plunger, you might still want it for the nudge improvements. The modified version also works with any other input controller, so you can get the enhanced nudging effects even if you're using a different plunger/nudge kit. The big change in the modified versions is a "filter" for accelerometer input that's designed to make the response to cabinet nudges more realistic. It also makes the response more subdued than in the standard VP, so it's not to everyone's taste. The downloads include both the updated executables and the source code changes, in case you want to merge the changes into your own custom version(s).

    Note! These features are now standard in the official VP releases, so you don't need my custom builds if you're using 9.9.1 or later and/or VP 10. I don't think there's any reason to use my versions instead of the latest official ones, and in fact I'd encourage you to use the official releases since they're more up to date, but I'm leaving my builds available just in case. In the official versions, look for the checkbox "Enable Nudge Filter" in the Keys preferences dialog. My custom versions don't include that checkbox; they just enable the filter unconditionally.
  • Output circuit shopping list: This is a saved shopping cart at with the parts needed to build one copy of the high-power output circuit for the LedWiz emulator feature, for use with the standalone KL25Z (that is, without the expansion boards). The quantities in the cart are for one output channel, so if you want N outputs, simply multiply the quantities by the N, with one exception: you only need one ULN2803 transistor array chip for each eight output circuits. If you're using the expansion boards, you won't need any of this, since the boards provide their own high-power outputs.
  • Cary Owens' optical sensor housing: A 3D-printable design for a housing/mounting bracket for the optical plunger sensor, designed by Cary Owens. This makes it easy to mount the sensor.
  • Lemming77's potentiometer mounting bracket and shooter rod connecter: Sketchup designs for 3D-printable parts for mounting a slide potentiometer as the plunger sensor. These were designed for a particular slide potentiometer that used to be available from an seller but is no longer listed. You can probably use this design as a starting point for other similar devices; just check the dimensions before committing the design to plastic.

Copyright and License

The Pinscape firmware is copyright 2014, 2021 by Michael J Roberts. It's released under an MIT open-source license. See License.

Warning to VirtuaPin Kit Owners

This software isn't designed as a replacement for the VirtuaPin plunger kit's firmware. If you bought the VirtuaPin kit, I recommend that you don't install this software. The KL25Z can only run one firmware program at a time, so if you install the Pinscape firmware on your KL25Z, it will replace and erase your existing VirtuaPin proprietary firmware. If you do this, the only way to restore your VirtuaPin firmware is to physically ship the KL25Z back to VirtuaPin and ask them to re-flash it. They don't allow you to do this at home, and they don't even allow you to back up your firmware, since they want to protect their proprietary software from copying. For all of these reasons, if you want to run the Pinscape software, I strongly recommend that you buy a "blank" retail KL25Z to use with Pinscape. They only cost about $15 and are available at several online retailers, including Amazon, Mouser, and eBay. The blank retail boards don't come with any proprietary firmware pre-installed, so installing Pinscape won't delete anything that you paid extra for.

With those warnings in mind, if you're absolutely sure that you don't mind permanently erasing your VirtuaPin firmware, it is at least possible to use Pinscape as a replacement for the VirtuaPin firmware. Pinscape uses the same button wiring conventions as the VirtuaPin setup, so you can keep your buttons (although you'll have to update the GPIO pin mappings in the Config Tool to match your physical wiring). As of the June, 2021 firmware, the Vishay VCNL4010 plunger sensor that comes with the VirtuaPin v3 plunger kit is supported, so you can also keep your plunger, if you have that chip. (You should check to be sure that's the sensor chip you have before committing to this route, if keeping the plunger sensor is important to you. The older VirtuaPin plunger kits came with different IR sensors that the Pinscape software doesn't handle.)



File content as of revision 4:02c7cd7b2183:

#include "mbed.h"
#include "USBJoystick.h"
#include "MMA8451Q.h"
#include "tsl1410r.h"
#include "FreescaleIAP.h"
#include "crc32.h"

// customization of the joystick class to expose connect/suspend status
class MyUSBJoystick: public USBJoystick
    MyUSBJoystick(uint16_t vendor_id, uint16_t product_id, uint16_t product_release) 
        : USBJoystick(vendor_id, product_id, product_release, false)
        suspended_ = false;
    int isConnected() { return configured(); }
    int isSuspended() const { return suspended_; }
    virtual void suspendStateChanged(unsigned int suspended)
        { suspended_ = suspended; }

    int suspended_; 

// On-board RGB LED elements - we use these for diagnostic displays.
DigitalOut ledR(LED1), ledG(LED2), ledB(LED3);

// calibration button - switch input and LED output
DigitalIn calBtn(PTE29);
DigitalOut calBtnLed(PTE23);

static int pbaIdx = 0;

// on/off state for each LedWiz output
static uint8_t wizOn[32];

// profile (brightness/blink) state for each LedWiz output
static uint8_t wizVal[32] = {
    0, 0, 0, 0, 0, 0, 0, 0,
    0, 0, 0, 0, 0, 0, 0, 0,
    0, 0, 0, 0, 0, 0, 0, 0,
    0, 0, 0, 0, 0, 0, 0, 0

static float wizState(int idx)
    if (wizOn[idx]) {
        // on - map profile brightness state to PWM level
        uint8_t val = wizVal[idx];
        if (val >= 1 && val <= 48)
            return 1.0 - val/48.0;
        else if (val >= 129 && val <= 132)
            return 0.0;
            return 1.0;
    else {
        // off
        return 1.0;

static void updateWizOuts()
    ledR = wizState(0);
    ledG = wizState(1);
    ledB = wizState(2);

struct AccPrv
    AccPrv() : x(0), y(0) { }
    float x;
    float y;
    double dist(AccPrv &b)
        float dx = x - b.x, dy = y - b.y;
        return sqrt(dx*dx + dy*dy);

// Non-volatile memory structure.  We store persistent a small
// amount of persistent data in flash memory to retain calibration
// data between sessions.
struct NVM
    // checksum - we use this to determine if the flash record
    // has been initialized
    uint32_t checksum;

    // signature value
    static const uint32_t SIGNATURE = 0x4D4A522A;
    static const uint16_t VERSION = 0x0002;
    // stored data (excluding the checksum)
        // signature and version - further verification that we have valid 
        // initialized data
        uint32_t sig;
        uint16_t vsn;
        // direction - 0 means unknown, 1 means bright end is pixel 0, 2 means reversed
        uint8_t dir;

        // plunger calibration min and max
        int plungerMin;
        int plungerMax;
    } d;

// Accelerometer handler
const int MMA8451_I2C_ADDRESS = (0x1d<<1);
class Accel
    Accel(PinName sda, PinName scl, int i2cAddr, PinName irqPin)
        : mma_(sda, scl, i2cAddr), intIn_(irqPin)
        // set the initial ball velocity to zero
        vx_ = vy_ = 0;
        // set the initial raw acceleration reading to zero
        xRaw_ = yRaw_ = 0;

        // enable the interrupt
        mma_.setInterruptMode(irqPin == PTA14 ? 1 : 2);
        // set up the interrupt handler
        intIn_.rise(this, &Accel::isr);
        // read the current registers to clear the data ready flag
        float z;
        mma_.getAccXYZ(xRaw_, yRaw_, z);

        // start our timers
    void get(float &x, float &y, float &rx, float &ry) 
         // disable interrupts while manipulating the shared data
         // read the shared data and store locally for calculations
         float vx = vx_, vy = vy_, xRaw = xRaw_, yRaw = yRaw_;

         // reset the velocity
         vx_ = vy_ = 0;
         // get the time since the last get() sample
         float dt = tGet_.read_us()/1.0e6;
         // done manipulating the shared data
         // calculate the acceleration since the last get(): a = dv/dt
         x = vx/dt;
         y = vy/dt;         
         // return the raw accelerometer data in rx,ry
         rx = xRaw;
         ry = yRaw;
    // interrupt handler
    void isr()
        // Read the axes.  Note that we have to read all three axes
        // (even though we only really use x and y) in order to clear
        // the "data ready" status bit in the accelerometer.  The
        // interrupt only occurs when the "ready" bit transitions from
        // off to on, so we have to make sure it's off.
        float z;
        mma_.getAccXYZ(xRaw_, yRaw_, z);
        // calculate the time since the last interrupt
        float dt = tInt_.read_us()/1.0e6;
        // Accelerate the model ball: v = a*dt.  Assume that the raw
        // data from the accelerometer reflects the average physical
        // acceleration over the interval since the last sample.
        vx_ += xRaw_ * dt;
        vy_ += yRaw_ * dt;
    // current modeled ball velocity
    float vx_, vy_;
    // last raw axis readings
    float xRaw_, yRaw_;
    // underlying accelerometer object
    MMA8451Q mma_;
    // interrupt router
    InterruptIn intIn_;
    // timer for measuring time between get() samples
    Timer tGet_;
    // timer for measuring time between interrupts
    Timer tInt_;

int main(void)
    // turn off our on-board indicator LED
    ledR = 1;
    ledG = 1;
    ledB = 1;
    // set up a flash memory controller
    FreescaleIAP iap;
    // use the last sector of flash for our non-volatile memory structure
    int flash_addr = (iap.flash_size() - SECTOR_SIZE);
    NVM *flash = (NVM *)flash_addr;
    NVM cfg;
    // check for valid flash
    bool flash_valid = (flash->d.sig == flash->SIGNATURE 
                        && flash->d.vsn == flash->VERSION
                        && flash->checksum == CRC32(&flash->d, sizeof(flash->d)));
    // Number of pixels we read from the sensor on each frame.  This can be
    // less than the physical pixel count if desired; we'll read every nth
    // piexl if so.  E.g., with a 1280-pixel physical sensor, if npix is 320,
    // we'll read every 4th pixel.  VP doesn't seem to have very high
    // resolution internally for the plunger, so it's probably not necessary
    // to use the full resolution of the sensor - about 160 pixels seems
    // perfectly adequate.  We can read the sensor faster (and thus provide
    // a higher refresh rate) if we read fewer pixels in each frame.
    const int npix = 160;

    // if the flash is valid, load it; otherwise initialize to defaults
    if (flash_valid) {
        memcpy(&cfg, flash, sizeof(cfg));
        printf("Flash restored: plunger min=%d, max=%d\r\n", 
            cfg.d.plungerMin, cfg.d.plungerMax);
    else {
        printf("Factory reset\r\n");
        cfg.d.sig = cfg.SIGNATURE;
        cfg.d.vsn = cfg.VERSION;
        cfg.d.plungerMin = 0;
        cfg.d.plungerMax = npix;
    // plunger calibration button debounce timer
    Timer calBtnTimer;
    int calBtnDownTime = 0;
    int calBtnLit = false;
    // Calibration button state:
    //  0 = not pushed
    //  1 = pushed, not yet debounced
    //  2 = pushed, debounced, waiting for hold time
    //  3 = pushed, hold time completed - in calibration mode
    int calBtnState = 0;
    // set up a timer for our heartbeat indicator
    Timer hbTimer;
    int t0Hb = hbTimer.read_ms();
    int hb = 0;
    // set a timer for accelerometer auto-centering
    Timer acTimer;
    int t0ac = acTimer.read_ms();
    // Create the joystick USB client
    MyUSBJoystick js(0xFAFA, 0x00F7, 0x0003);

    // create the accelerometer object
    Accel accel(PTE25, PTE24, MMA8451_I2C_ADDRESS, PTA15);
    // create the CCD array object
    TSL1410R ccd(PTE20, PTE21, PTB0);
    // recent accelerometer readings, for auto centering
    int iAccPrv = 0, nAccPrv = 0;
    const int maxAccPrv = 5;
    AccPrv accPrv[maxAccPrv];

    // last accelerometer report, in mouse coordinates
    int x = 127, y = 127, z = 0;

    // raw accelerator centerpoint, on the unit interval (-1.0 .. +1.0)
    float xCenter = 0.0, yCenter = 0.0;    
    // start the first CCD integration cycle

    // we're all set up - now just loop, processing sensor reports and 
    // host requests
    for (;;)
        // Look for an incoming report.  Continue processing input as
        // long as there's anything pending - this ensures that we
        // handle input in as timely a fashion as possible by deferring
        // output tasks as long as there's input to process.
        HID_REPORT report;
        while (js.readNB(&report) && report.length == 8)
            uint8_t *data =;
            if (data[0] == 64) 
                // LWZ-SBA - first four bytes are bit-packed on/off flags
                // for the outputs; 5th byte is the pulse speed (0-7)
                //printf("LWZ-SBA %02x %02x %02x %02x ; %02x\r\n",
                //       data[1], data[2], data[3], data[4], data[5]);

                // update all on/off states
                for (int i = 0, bit = 1, ri = 1 ; i < 32 ; ++i, bit <<= 1)
                    if (bit == 0x100) {
                        bit = 1;
                    wizOn[i] = ((data[ri] & bit) != 0);
                // update the physical outputs
                // reset the PBA counter
                pbaIdx = 0;
                // LWZ-PBA - full state dump; each byte is one output
                // in the current bank.  pbaIdx keeps track of the bank;
                // this is incremented implicitly by each PBA message.
                //printf("LWZ-PBA[%d] %02x %02x %02x %02x %02x %02x %02x %02x\r\n",
                //       pbaIdx, data[0], data[1], data[2], data[3], data[4], data[5], data[6], data[7]);

                // update all output profile settings
                for (int i = 0 ; i < 8 ; ++i)
                    wizVal[pbaIdx + i] = data[i];

                // update the physical LED state if this is the last bank                    
                if (pbaIdx == 24)

                // advance to the next bank
                pbaIdx = (pbaIdx + 8) & 31;
        // check for plunger calibration
        if (!calBtn)
            // check the state
            switch (calBtnState)
            case 0: 
                // button not yet pushed - start debouncing
                calBtnDownTime = calBtnTimer.read_ms();
                calBtnState = 1;
            case 1:
                // pushed, not yet debounced - if the debounce time has
                // passed, start the hold period
                if (calBtnTimer.read_ms() - calBtnDownTime > 50)
                    calBtnState = 2;
            case 2:
                // in the hold period - if the button has been held down
                // for the entire hold period, move to calibration mode
                if (calBtnTimer.read_ms() - calBtnDownTime > 2050)
                    // enter calibration mode
                    calBtnState = 3;
                    // reset the calibration limits
                    cfg.d.plungerMax = 0;
                    cfg.d.plungerMin = npix;
            case 3:
                // Already in calibration mode - pushing the button in this
                // state doesn't change the current state, but we won't leave
                // this state as long as it's held down.  We can simply do
                // nothing here.
            // Button released.  If we're in calibration mode, and
            // the calibration time has elapsed, end the calibration
            // and save the results to flash.
            // Otherwise, return to the base state without saving anything.
            // If the button is released before we make it to calibration
            // mode, it simply cancels the attempt.
            if (calBtnState == 3
                && calBtnTimer.read_ms() - calBtnDownTime > 17500)
                // exit calibration mode
                calBtnState = 0;
                // Save the current configuration state to flash, so that it
                // will be preserved through power off.  Update the checksum
                // first so that we recognize the flash record as valid.
                cfg.checksum = CRC32(&cfg.d, sizeof(cfg.d));
                iap.program_flash(flash_addr, &cfg, sizeof(cfg));
                // the flash state is now valid
                flash_valid = true;
            else if (calBtnState != 3)
                // didn't make it to calibration mode - cancel the operation
                calBtnState = 0;
        // light/flash the calibration button light, if applicable
        int newCalBtnLit = calBtnLit;
        switch (calBtnState)
        case 2:
            // in the hold period - flash the light
            newCalBtnLit = (((calBtnTimer.read_ms() - calBtnDownTime)/250) & 1);
        case 3:
            // calibration mode - show steady on
            newCalBtnLit = true;
            // not calibrating/holding - show steady off
            newCalBtnLit = false;
        // light or flash the external calibration button LED, and 
        // do the same with the on-board blue LED
        if (calBtnLit != newCalBtnLit)
            calBtnLit = newCalBtnLit;
            if (calBtnLit) {
                calBtnLed = 1;
                ledR = 1;
                ledG = 1;
                ledB = 1;
            else {
                calBtnLed = 0;
                ledR = 1;
                ledG = 1;
                ledB = 0;
        // read the plunger sensor
        int znew = z;
        uint16_t pix[npix];, npix);

        // get the average brightness at each end of the sensor
        long avg1 = (long(pix[0]) + long(pix[1]) + long(pix[2]) + long(pix[3]) + long(pix[4]))/5;
        long avg2 = (long(pix[npix-1]) + long(pix[npix-2]) + long(pix[npix-3]) + long(pix[npix-4]) + long(pix[npix-5]))/5;
        // figure the midpoint in the brightness; multiply by 3 so that we can
        // compare sums of three pixels at a time to smooth out noise
        long midpt = (avg1 + avg2)/2 * 3;
        // Work from the bright end to the dark end.  VP interprets the
        // Z axis value as the amount the plunger is pulled: the minimum
        // is the rest position, the maximum is fully pulled.  So we 
        // essentially want to report how much of the sensor is lit,
        // since this increases as the plunger is pulled back.
        int si = 1, di = 1;
        if (avg1 < avg2)
            si = npix - 2, di = -1;

        // scan for the midpoint     
        uint16_t *pixp = pix + si;           
        for (int n = 1 ; n < npix - 1 ; ++n, pixp += di)
            // if we've crossed the midpoint, report this position
            if (long(pixp[-1]) + long(pixp[0]) + long(pixp[1]) < midpt)
                // note the new position
                int pos = n;
                // if the bright end and dark end don't differ by enough, skip this
                // reading entirely - we must have an overexposed or underexposed frame
                if (labs(avg1 - avg2) < 0x3333)
                // Calibrate, or apply calibration, depending on the mode.
                // In either case, normalize to a 0-127 range.  VP appears to
                // ignore negative Z axis values.
                if (calBtnState == 3)
                    // calibrating - note if we're expanding the calibration envelope
                    if (pos < cfg.d.plungerMin)
                        cfg.d.plungerMin = pos;   
                    if (pos > cfg.d.plungerMax)
                        cfg.d.plungerMax = pos;
                    // normalize to the full physical range while calibrating
                    znew = int(float(pos)/npix * 127);
                    // running normally - normalize to the calibration range
                    if (pos < cfg.d.plungerMin)
                        pos = cfg.d.plungerMin;
                    if (pos > cfg.d.plungerMax)
                        pos = cfg.d.plungerMax;
                    znew = int(float(pos - cfg.d.plungerMin)
                        / (cfg.d.plungerMax - cfg.d.plungerMin + 1) * 127);
                // done
        // read the accelerometer
        float xa, ya, rxa, rya;
        accel.get(xa, ya, rxa, rya);
        // check for auto-centering every so often
        if (acTimer.read_ms() - t0ac > 1000) 
            // add the sample to the history list
            accPrv[iAccPrv].x = xa;
            accPrv[iAccPrv].y = ya;
            // store the slot
            iAccPrv += 1;
            iAccPrv %= maxAccPrv;
            nAccPrv += 1;
            // If we have a full complement, check for stability.  The
            // raw accelerometer input is in the rnage -4096 to 4096, but
            // the class cover normalizes to a unit interval (-1.0 .. +1.0).
            const float accTol = .005;
            if (nAccPrv >= maxAccPrv
                && accPrv[0].dist(accPrv[1]) < accTol
                && accPrv[0].dist(accPrv[2]) < accTol
                && accPrv[0].dist(accPrv[3]) < accTol
                && accPrv[0].dist(accPrv[4]) < accTol)
                // figure the new center
                xCenter = (accPrv[0].x + accPrv[1].x + accPrv[2].x + accPrv[3].x + accPrv[4].x)/5.0;
                yCenter = (accPrv[0].y + accPrv[1].y + accPrv[2].y + accPrv[3].y + accPrv[4].y)/5.0;
            // reset the auto-center timer
            t0ac = acTimer.read_ms();
        // adjust for our auto centering
        xa -= xCenter;
        ya -= yCenter;
        // confine to the unit interval
        if (xa < -1.0) xa = -1.0;
        if (xa > 1.0) xa = 1.0;
        if (ya < -1.0) ya = -1.0;
        if (ya > 1.0) ya = 1.0;

        // figure the new mouse report data
        int xnew = (int)(127 * xa);
        int ynew = (int)(127 * ya);

        // store the updated joystick coordinates
        x = xnew;
        y = ynew;
        z = znew;
        // if we're in USB suspend or disconnect mode, spin
        if (js.isSuspended() || !js.isConnected())
            // go dark (turn off the indicator LEDs)
            ledG = 1;
            ledB = 1;
            ledR = 1;
            // wait until we're connected and come out of suspend mode
            for (uint32_t n = 0 ; js.isSuspended() || !js.isConnected() ; ++n)
                // spin for a bit
                // if we're suspended, do a brief red flash; otherwise do a long red flash
                if (js.isSuspended())
                    // suspended - flash briefly ever few seconds
                    if (n % 3 == 0)
                        ledR = 0;
                        ledR = 1;
                    // running, not connected - flash red
                    ledR = !ledR;

        // Send the status report.  It doesn't really matter what
        // coordinate system we use, since Visual Pinball has config
        // options for rotations and axis reversals, but reversing y
        // at the device level seems to produce the most intuitive 
        // results for the Windows joystick control panel view, which
        // is an easy way to check that the device is working.
        js.update(x, -y, z, int(rxa*127), int(rya*127), 0);
        // show a heartbeat flash in blue every so often if not in 
        // calibration mode
        if (calBtnState < 2 && hbTimer.read_ms() - t0Hb > 1000) 
            if (js.isSuspended())
                // suspended - turn off the LEDs entirely
                ledR = 1;
                ledG = 1;
                ledB = 1;
            else if (!js.isConnected())
                // not connected - flash red
                hb = !hb;
                ledR = (hb ? 0 : 1);
                ledG = 1;
                ledB = 1;
            else if (flash_valid)
                // connected, NVM valid - flash blue/green
                hb = !hb;
                ledR = 1;
                ledG = (hb ? 0 : 1);
                ledB = (hb ? 1 : 0);
                // connected, factory reset - flash yellow/green
                hb = !hb;
                ledR = (hb ? 0 : 1);
                ledG = 0;
                ledB = 1;
            // reset the heartbeat timer
            t0Hb = hbTimer.read_ms();