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 potentionmeter (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 VirtuaPin kit uses the same KL25Z microcontroller that Pinscape uses, but the rest of its hardware is different and incompatible. In particular, the Pinscape firmware doesn't include support for the IR proximity sensor used in the VirtuaPin plunger kit, so you won't be able to use your plunger device with the Pinscape firmware. In addition, the VirtuaPin setup uses a different set of GPIO pins for the button inputs from the Pinscape defaults, so if you do install the Pinscape firmware, you'll have to go into the Config Tool and reassign all of the buttons to match the VirtuaPin wiring.


12 months ago

File content as of revision 109:310ac82cbbee:

// Plunger sensor type for bar-code based absolute position encoders.
// This type of sensor uses an optical sensor that moves with the plunger
// along a guide rail with printed bar codes along its length that encode
// the absolute position at each point.  We figure the plunger position
// by reading the bar code and decoding it into a position figure.
// The bar code has to be encoded in a specific format that we recognize.
// We use a reflected Gray code, optically encoded in black/white pixel
// patterns.  Each bit is represented by a fixed-width area.  Half the
// pixels in every bit are white, and half are black.  A '0' bit is
// represented by black pixels in the left half and white pixels in the
// right half, and a '1' bit is white on the left and black on the right.
// To read a bit, we identify the set of pixels covering the bit's fixed
// area in the code, then we see if the left or right half is brighter.
// (This optical encoding scheme is based on Manchester coding, which is 
// normally used in the context of serial protocols, but translates to 
// bar codes straightforwardly.  Replace the serial protocol's time
// dimension with the spatial dimension across the bar, and replace the
// high/low wire voltage levels with white/black pixels.)
// Gray codes are ideal for this type of application.  Gray codes are
// defined such that each code point differs in exactly one bit from each
// adjacent code point.  This provides natural error correction when used
// as a position scale, since any single-bit error will yield a code point 
// reading that's only one spot off from the true position.  So a bit read
// error acts like a reduction in precision.  Likewise, any time the sensor
// is halfway between two code points, only one bit will be ambiguous, so
// the reading will come out as one of points on either side of the true
// position.  Finally, motion blur will have the same effect, of creating
// ambiguity in the least significant bits, and thus giving us a reading
// that's correct to as many bits as we can make out.
// The half-and-half optical coding also has good properties for our
// purposes.  The fixed-width bit regions require essentially no CPU work
// to find the bits, which is good because we're using a fairly slow CPU.
// The half white/half black coding of each pixel makes every pixel 
// self-relative in terms of brightness, so we don't need to figure the 
// black and white thresholds globally for the whole image.  That makes 
// the physical device engineering and installation easier because the 
// software can tolerate a fairly wide range of lighting conditions.


#include "plunger.h"

// Gray code to binary mapping for our special coding.  This is a custom
// 7-bit code, minimum run length 6, 110 positions populated.  The minimum
// run length is the minimum number of consecutive code points where each
// bit must remain fixed.  For out optical coding, this defines the smallest
// "island" size for a black or white bar horizontally.  Small features are
// prone to light scattering that makes them appear gray on the sensor.
// Larger features are less subject to scatter, making them easier to 
// distinguish by brightness level.
static const uint8_t grayToBin[] = {
   0,   1,  83,   2,  71, 100,  84,   3,  69, 102,  82, 128,  70, 101,  57,   4,    // 0-15
  35,  50,  36,  37,  86,  87,  85, 128,  34, 103,  21, 104, 128, 128,  20,   5,    // 16-31
  11, 128,  24,  25,  98,  99,  97,  40,  68,  67,  81,  80,  55,  54,  56,  41,    // 32-47
  10,  51,  23,  38, 128,  52, 128,  39,   9,  66,  22, 128,   8,  53,   7,   6,    // 48-63
  47,  14,  60, 128,  72,  15,  59,  16,  46,  91,  93,  92,  45, 128,  58,  17,    // 64-79
  48,  49,  61,  62,  73,  88,  74,  75,  33,  90, 106, 105,  32,  89,  19,  18,    // 80-95
  12,  13,  95,  26, 128,  28,  96,  27, 128, 128,  94,  79,  44,  29,  43,  42,    // 96-111
 128,  64, 128,  63, 110, 128, 109,  76, 128,  65, 107,  78,  31,  30, 108,  77     // 112-127

// Auto-exposure counter
class BarCodeExposureCounter
        nDark = 0;
        nBright = 0;
        nZero = 0;
        nSat = 0;
    inline void count(int pix)
        if (pix <= 2)
        else if (pix < 12)
        else if (pix >= 253)
        else if (pix > 200)
    int nDark;      // dark pixels
    int nBright;    // bright pixels
    int nZero;      // pixels at zero brightness
    int nSat;       // pixels at full saturation

// Base class for bar-code sensors
// This is a template class with template parameters for the bar
// code pixel structure.  The bar code layout is fixed for a given 
// sensor type.  We can assume fixed pixel sizes because we don't 
// have to process arbitrary images.  We only have to read scales 
// specially prepared for this application, so we can count on them
// being printed at an exact size relative to the sensor pixels.
// nBits = Number of bits in the code 
// leftBarWidth = Width in pixels of delimiting left bar.  The code is 
// delimited by a black bar on the "left" end, nearest pixel 0.  This 
// gives the pixel width of the bar.
// leftBarMaxOfs = Maximum offset of the delimiting bar from the left
// edge of the sensor (pixel 0), in pixels
// bitWidth = Width of each bit in pixels.  This is the width of the
// full bit, including both "half bits" - it's the full white/black or 
// black/white pattern area.

struct BarCodeProcessResult
    int pixofs;
    int raw;
    int mask;

template <int nBits, int leftBarWidth, int leftBarMaxOfs, int bitWidth>
class PlungerSensorBarCode: public PlungerSensorImage<BarCodeProcessResult>
    PlungerSensorBarCode(PlungerSensorImageInterface &sensor, int npix)
        : PlungerSensorImage(sensor, npix, (1 << nBits) - 1)
        startOfs = 0;

    // process a configuration change
    virtual void onConfigChange(int varno, Config &cfg)
        // check for bar-code variables
        switch (varno)
        case 20:
            // bar code offset
            startOfs = cfg.plunger.barCode.startPix;
        // do the generic work
        PlungerSensorImage::onConfigChange(varno, cfg);

    // process the image    
    virtual bool process(const uint8_t *pix, int npix, int &pos, BarCodeProcessResult &res)
        // adjust auto-exposure
        adjustExposure(pix, npix);
        // clear the result descriptor
        res.pixofs = 0;
        res.raw = 0;
        res.mask = 0;
#if 0 // $$$

        // scan from the left edge until we find the fixed '0' start bit
        for (int i = 0 ; i < leftBarMaxOfs ; ++i, ++pix)
            // check for the '0' bit
            if (readBit8(pix) == 0)
                // got it - skip the start bit
                pix += bitWidth;
                // read the gray code bits
                int gray = 0;
                for (int j = 0 ; j < nBits ; ++j, pix += bitWidth)
                    // read the bit; return failure if we can't decode a bit
                    int bit = readBit8(pix);
                    if (bit < 0)
                        return false;
                    // shift it into the code
                    gray = (gray << 1) | bit;
            // convert the gray code to binary
            int bin = grayToBin(gray);
            // compute the parity of the binary value
            int parity = 0;
            for (int j = 0 ; j < nBits ; ++j)
                parity ^= bin >> j;
            // figure the bit required for odd parity
            int odd = (parity & 0x01) ^ 0x01;
            // read the check bit
            int bit = readBit8(pix);
            if (pix < 0)
                return false;
            // check that it matches the expected parity
            if (bit != odd)
                return false;
            // success
            pos = bin;
            return true;
        // no code found
        return false;

        int barStart = leftBarMaxOfs/2;
        if (leftBarWidth != 0) // $$$
            // Find the black bar on the left side (nearest pixel 0) that
            // delimits the start of the bar code.  To find it, first figure
            // the average brightness over the left margin up to the maximum
            // allowable offset, then look for the bar by finding the first
            // bar-width run of pixels that are darker than the average.
            int lsum = 0;
            for (int x = 1 ; x <= leftBarMaxOfs ; ++x)
                lsum += pix[x];
            int lavg = lsum / leftBarMaxOfs;
            // now find the first dark edge
            for (int x = 0 ; x < leftBarMaxOfs ; ++x)
                // if this pixel is dark, and one of the next two is dark,
                // take it as the edge
                if (pix[x] < lavg && (pix[x+1] < lavg || pix[x+2] < lavg))
                    // move past the delimier
                    barStart = x + leftBarWidth;
            // start at the fixed pixel offset
            barStart = startOfs;

        // Start with zero in the barcode and success mask.  The mask
        // indicates which bits we were able to read successfully: a
        // '1' bit in the mask indicates that the corresponding bit
        // position in 'barcode' was successfully read, a '0' bit means
        // that the image was too fuzzy to read.
        int barcode = 0, mask = 0;

        // Scan the bits
        for (int bit = 0, x0 = barStart; bit < nBits ; ++bit, x0 += bitWidth)
#if 0
            // Figure the extent of this bit.  The last bit is double
            // the width of the other bits, to give us a better chance
            // of making out the small features of the last bit.
            int w = bitWidth;
            if (bit == nBits - 1) w *= 2;
            // width of the bit
            const int w = bitWidth;

            // figure the bit's internal pixel layout
            int halfBitWidth = w / 2;
            int x1 = x0 + halfBitWidth;     // midpoint
            int x2 = x0 + w;                // right edge
            // make sure we didn't go out of bounds
            if (x1 > npix) x1 = npix;
            if (x2 > npix) x2 = npix;

#if 0
            // get the average of the pixels over the bit
            int sum = 0;
            for (int x = x0 ; x < x2 ; ++x)
                sum += pix[x];
            int avg = sum / w;
            // Scan the left and right sections.  Classify each
            // section according to whether the majority of its
            // pixels are above or below the local average.
            int lsum = 0, rsum = 0;
            for (int x = x0 + 1 ; x < x1 - 1 ; ++x)
                lsum += (pix[x] < avg ? 0 : 1);
            for (int x = x1 + 1 ; x < x2 - 1 ; ++x)
                rsum += (pix[x] < avg ? 0 : 1);
            // Sum the pixel readings in each half-bit.  Ignore
            // the first and last bit of each section, since these
            // could be contaminated with scattered light from the
            // adjacent half-bit.  On the right half, hew to the 
            // right side if the overall pixel width is odd. 
            int lsum = 0, rsum = 0;
            for (int x = x0 + 1 ; x < x1 - 1 ; ++x)
                lsum += pix[x];
            for (int x = x2 - halfBitWidth + 1 ; x < x2 - 1 ; ++x)
                rsum += pix[x];
            // shift a zero bit into the code and success mask
            barcode <<= 1;
            mask <<= 1;

            // Brightness difference required per pixel.  Higher values
            // require greater contrast to make a reading, which reduces
            // spurious readings at the cost of reducing the overall 
            // success rate.  The right level depends on the quality of
            // the optical system.  Setting this to zero makes us maximally
            // tolerant of low-contrast images, allowing for the simplest
            // optical system.  Our simple optical system suffers from
            // poor focus, which in turn causes poor contrast in small
            // features.
            const int minDelta = 2;

            // see if we could tell the difference in brightness
            int delta = lsum - rsum;
            if (delta < 0) delta = -delta;
            if (delta > minDelta * w/2)
                // got it - black/white = 0, white/black = 1
                if (lsum > rsum) barcode |= 1;
                mask |= 1;

        // decode the Gray code value to binary
        pos = grayToBin[barcode];
        // set the results descriptor structure
        res.pixofs = barStart;
        res.raw = barcode;
        res.mask = mask;
        // return success if we decoded all bits, and the Gray-to-binary
        // mapping was populated
        return pos != (1 << nBits) && mask == ((1 << nBits) - 1);
    // read a bar starting at the given pixel
    int readBit8(const uint8_t *pix)
        // pull out the pixels for the bar
        uint8_t s[8];
        memcpy(s, pix, 8);
        // sort them in brightness order (using an 8-element network sort)
#define SWAP(a, b) if (s[a] > s[b]) { uint8_t tmp = s[a]; s[a] = s[b]; s[b] = tmp; }
        SWAP(0, 1);
        SWAP(2, 3);
        SWAP(0, 2);
        SWAP(1, 3);
        SWAP(1, 2);
        SWAP(4, 5);
        SWAP(6, 7);
        SWAP(4, 6);
        SWAP(5, 7);
        SWAP(5, 6);
        SWAP(0, 4);
        SWAP(1, 5);
        SWAP(1, 4);
        SWAP(2, 6);
        SWAP(3, 7);
        SWAP(3, 6);
        SWAP(2, 4);
        SWAP(3, 5);
        SWAP(3, 4);
#undef SWAP
        // figure the median brightness
        int median = (int(s[3]) + s[4] + 1) / 2;
        // count pixels below the median on each side
        int ldark = 0, rdark = 0;
        for (int i = 0 ; i < 3 ; ++i)
            if (pix[i] < median)
        for (int i = 4 ; i < 8 ; ++i)
            if (pix[i] < median)
        // we need >=3 dark + >=3 light or vice versa
        if (ldark >= 3 && rdark <= 1)
            // dark + light = '0' bit
            return 0;
        if (ldark <= 1 && rdark >= 3)
            // light + dark = '1' bit
            return 1;
            // ambiguous bit
            return -1;

    // bar code sensor orientation is fixed
    virtual int getOrientation() const { return 1; }
    // send extra status report headers
    virtual void extraStatusHeaders(USBJoystick &js, BarCodeProcessResult &res)
        // Send the bar code status report.  We use coding type 1 (Gray code,
        // Manchester pixel coding).
        js.sendPlungerStatusBarcode(nBits, 1, res.pixofs, bitWidth, res.raw, res.mask);
    // adjust the exposure
    void adjustExposure(const uint8_t *pix, int npix)
#if 1
        // The Manchester code has a nice property for auto exposure
        // control: each bit area has equal numbers of white and black
        // pixels.  So we know exactly how the overall population of
        // pixels has to look: the bit area will be 50% black and 50%
        // white, and the margins will be all white.  For maximum
        // contrast, target an exposure level where the black pixels
        // are all below a certain brightness level and the white
        // pixels are all above.  Start by figuring the number of
        // pixels above and below.
        const int medianTarget = 160;
        int nBelow = 0;
        for (int i = 0 ; i < npix ; ++i)
            if (pix[i] < medianTarget)
        // Figure the desired number of black pixels: the left bar is
        // all black pixels, and 50% of each bit is black pixels.
        int targetBelow = leftBarWidth + (nBits * bitWidth)/2;
        // Increase exposure time if too many pixels are below the
        // halfway point; decrease it if too many pixels are above.
        int d = nBelow - targetBelow;
        if (d > 5 || d < -5)
            axcTime += d;
#elif 0 //$$$
        // Count exposure levels of pixels in the left and right margins
        BarCodeExposureCounter counter;
        for (int i = 0 ; i < leftBarMaxOfs/2 ; ++i)
            // count the pixels at the left and right margins
            counter.count(pix[npix - i - 1]);
        // The margin is all white, so try to get all of these pixels
        // in the bright range, but not saturated.  That should give us
        // the best overall contrast throughout the image.
        if (counter.nSat > 0)
            // overexposed - reduce exposure time
            if (axcTime > 5)
                axcTime -= 5;
                axcTime = 0;
        else if (counter.nBright < leftBarMaxOfs)
            // they're not all in the bright range - increase exposure time
            axcTime += 5;

#else // $$$
        // Count the number of pixels near total darkness and
        // total saturation
        int nZero = 0, nDark = 0, nBri = 0, nSat = 0;
        for (int i = 0 ; i < npix ; ++i)
            int pi = pix[i];
            if (pi <= 2)
            else if (pi < 12)
            else if (pi >= 254)
            else if (pi > 242)
        // If more than 30% of pixels are near total darkness, increase
        // the exposure time.  If more than 30% are near total saturation,
        // decrease the exposure time.
        int pct5 = uint32_t(npix * 3277) >> 16;
        int pct30 = uint32_t(npix * 19661) >> 16;
        int pct50 = uint32_t(npix) >> 1;
        if (nSat == 0)
            // no saturated pixels - increase exposure time
            axcTime += 5;
        else if (nSat > pct5)
            if (axcTime > 5)
                axcTime -= 5;
                axcTime = 0;
        else if (nZero == 0)
            // no totally dark pixels - decrease exposure time
            if (axcTime > 5)
                axcTime -= 5;
                axcTime = 0;
        else if (nZero > pct5)
            axcTime += 5;
        else if (nZero > pct30 || (nDark > pct50 && nSat < pct30))
            // very dark - increase exposure time a lot
            if (axcTime < 450)
                axcTime += 50;
        else if (nDark > pct30 && nSat < pct30)
            // dark - increase exposure time a bit
            if (axcTime < 490)
                axcTime += 10;
        else if (nSat > pct30 || (nBri > pct50 && nDark < pct30))
            // very overexposed - decrease exposure time a lot
            if (axcTime > 50)
                axcTime -= 50;
                axcTime = 0;
        else if (nBri > pct30 && nDark < pct30)
            // overexposed - decrease exposure time a little
            if (axcTime > 10)
                axcTime -= 10;
                axcTime = 0;
        // don't allow the exposure time to go below 0 or over 2.5ms
        if (int(axcTime) < 0)
            axcTime = 0;
        if (axcTime > 2500)
            axcTime = 2500;

#if 0
    // convert a reflected Gray code value (up to 16 bits) to binary
    static inline int grayToBin(int grayval)
        int temp = grayval ^ (grayval >> 8);
        temp ^= (temp >> 4);
        temp ^= (temp >> 2);
        temp ^= (temp >> 1);
        return temp;

    // bar code starting pixel offset
    int startOfs;