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 implementation for rotary absolute encoders
// This implements the plunger interfaces for rotary absolute encoders.  A
// rotary encoder measures the angle of a rotating shaft.  An absolute encoder
// is one where the microcontroller can ask the sensor for its current angular
// position at any time.  (As opposed to incremental encoders, which don't have
// any notion of their current position, but can only signal the host on each
// change in position.)
// For plunger sensing, we can convert the plunger's linear motion into angular
// motion using a mechanical link between the plunger rod and a rotating shaft 
// positioned at a fixed point, somewhere nearby, but away from the plunger's 
// axis of motion:
//    =X=======================|===   <- plunger, X = connector attachment point
//      \
//       \                            <- connector between plunger and shaft
//        \
//         *                          <- rotating shaft, at a fixed position
// As the plunger moves, the angle of the connector relative to the fixed
// shaft position changes in a predictable way, so we can infer the plunger's
// linear position at any given time by measuring the current rotational
// angle of the shaft.
// The mechanical diagram above is, obviously, simplified for ASCII art's sake.
// What's not shown is that the distance between the rotating shaft and the
// "X" connection point on the plunger varies as the plunger moves, so the
// mechanical linkage requires some way to accommodate that changing length.
// If the connector is a rigid rod, it has to be able to slide at one or
// the other connection points.  Alternatively, rather than using a rigid
// linkage, we can use a spring or elastic band.  We leave these details up 
// to the mechanical design, since the software isn't affected by that, as 
// long as the basic relationship between linear and angular motion as shown
// in the diagram is achieved.
// Translating the angle to a linear position
// There are two complications to translating the angular reading back to
// a linear plunger position.
// 1. We have to consider the sensor's zero point to be arbitrary, because
// these sorts of sensors don't typically give the user a way to align the
// zero point at a desired physical position.  The zero point will just be
// wherever it ends up after installation.  The zero point could easily end 
// up being somewhere in the middle of the plunger's travel range, which
// means that readings might "wrap" - e.g., we might see a series of readings 
// when the plunger is moving in one direction like this: 4050, 4070, 4090, 
// 14, 34 (note how we "wrapped" past some maximum angle reading for the
// sensor and went back to zero, then continued from there).
// To deal with this, we have to make a couple of assumptions:
//   - The park position is at about 1/6 of the overall travel range
//   - The total angular travel range is less than one full revolution
// With those assumptions in hand, we can bias the raw readings to the
// park position, and then take them modulo the raw scale.  That will
// ensure that readings wrap properly, regardless of where the raw zero
// point lies.
// 2. Going back to the original diagram, you can see that there's some
// trigonometry required to interpret the sensor's angular reading as a
// linear position on the plunger axis, which is of course what we need
// to report to the PC software.
// Let's use the vertical line between the plunger and the rotation point
// as the zero-degree reference point.  To figure the plunger position, 
// we need to figure the difference between the raw angle reading and the
// zero-degree point; call this theta.  Let L be the position of the plunger
// relative to the vertical reference point, let D be the length of the 
// vertical reference point line, and let H by the distance from the rotation 
// point to the plunger connection point.  This is a right triangle with 
// hypotenuse H and sides L and D.  D is a constant, because the rotation 
// point never moves, and the plunger never moves vertically.  Thus we can
// calculate D = H*cos(theta) and L = H*sin(theta).  D is a constant, so
// we can figure H = D/cos(theta) hence L = D*sin(theta)/cos(theta) or
// D*tan(theta).  If we wanted to know the true position in real-world
// units, we'd have to know D, but only need arbitrary linear units, so
// we can choose whatever value for D we find convenient: in particular,
// a value that gives us the desired range and resolution for the final
// result.
// Note that the tangent diverges at +/-90 degrees, but that's okay,
// because the mechanical setup we've described is inherently constrained
// to stay well within those limits.  This would even be true for an 
// arbitrarily long range of motion along the travel axis, but we don't
// even have to worry about that since we have such a well-defined range
// of travel (of only about 3") to track.
// There's still one big piece missing here: we somehow have to know where
// that vertical zero point lies.  That's something we can only learn by
// calibration.  Unfortunately, we don't have a good way to detect this
// directly.  We *could* ask the user to look inside the cabinet and press
// a button when the needle is straight up, but that seems too cumbersome
// for the user, not to mention terribly imprecise.  So we'll approach this
// from the other direction: we'll assume a particular placement of the
// rotation point relative to the travel range, and we'll provide
// installation instructions to achieve that assumed alignment.
// The full range we actually have after calibration consists of the park
// position and the maximum retracted position.  We could in principle also
// calibrate the maximum forward position, but that can't be read as reliably
// as the other two, because the barrel spring makes it difficult for the 
// user to be sure they've pushed it all the way forward.  Since we can 
// extract the information we need from the park and max retract positions,
// it's better to rely on those alone and not ask for information that the
// user can't as easily provide.  Given these positions, AND the assumption
// that the rotation point is at the midpoint of the plunger travel range,
// we can do some grungy trig work to come up with a formula for the angle 
// between the park position and the vertical:
//    let C1 = 1 1/32" (distance from midpoint to park),
//        C2 = 1 17/32" (distance from midpoint to max retract),
//        C = C2/C1 = 1.48484849,
//        alpha = angle from park to vertical,
//        beta = angle from max retract to vertical
//        theta = alpha + beta = angle from park to max retract, known from calibration,
//        T = tan(theta);
//    then
//        alpha = atan(sqrt(4*T*T*C + C^2 + 2*C + 1) - C - 1)/(2*T*C))
// Did I mention this was grungy?  At any rate, everything going into that
// last equation is either constant or known from the calibration, so we 
// can pre-compute alpha and store it after each calibration operation.
// And once we've computed alpha, we can easily translate an angle reading 
// from the sensor to an angle relative to the vertical, which we can plug 
// into D*tan(angle) to convert to a linear position on the plunger axis.
// The final step is to scale that linear position into joystick reporting
// units.  Those units are arbitrary, so we don't have to relate this to any
// real-world lengths.  We can simply figure a scaling factor that maps the
// physical range to map to roughly the full range of the joystick units.
// If you're wondering how we derived that ugly formula, read on.  Start
// with the basic relationships D*tan(alpha) = C1 and D*tan(beta) = C2.
// This lets us write tan(beta) in terms of tan(alpha) as 
// C2/C1*tan(alpha) = C*tan(alpha).  We can combine this with an identity
// for the tan of a sum of angles:
//    tan(alpha + beta) = (tan(alpha) + tan(beta))/(1 - tan(alpha)*tan(beta))
// to obtain:
//    tan(theta) = tan(alpha + beta) = (1 + C*tan(alpha))/(1 - C*tan^2(alpha))
// Everything here except alpha is known, so we now have a quadratic equation
// for tan(alpha).  We can solve that by cranking through the normal algorithm
// for solving a quadratic equation, arriving at the solution above.
// Choosing an install position
// There are two competing factors in choosing the optimal "D".  On the one
// hand, you'd like D to be as large as possible, to maximum linearity of the
// tan function used to translate angle to linear position.  Higher linearity
// gives us greater immunity to variations in the precise centering of the
// rotation axis in the plunger travel range.  tan() is pretty linear (that
// is, tan(theta) is approximately proportional to theta) for small theta, 
// within about +/- 30 degrees.  On the other hand, you'd like D to be as 
// small as possible so that we get the largest overall angle range.  Our 
// sensor has a fixed angular resolution, so the more of the overall circle 
// we use, the more sensor increments we have over the range, and thus the 
// better effective linear resolution.
// Let's do some calculations for various "D" values (vertical distance 
// between rotation point and plunger rod).  We'll base our calculations
// on the AEAT-6012 sensor's 12-bit angular resolution.
//     D         theta(max)   eff dpi   theta(park)
//  -----------------------------------------------
//    1 17/32"    45 deg       341       34 deg
//    2"          37 deg       280       27 deg
//    2 21/32"    30 deg       228       21 deg
//    3 1/4"      25 deg       190       17 deg
//    4 3/16"     20 deg       152       14 deg
// I'd consider 50 dpi to be the minimum for acceptable performance, 100 dpi
// to be excellent, and anything above 300 dpi to be diminishing returns.  So
// for a 12-bit sensor, 2" looks like the sweet spot.  It doesn't take us far
// outside of the +/-30 deg zone of tan() linearity, and it achieves almost 
// 300 dpi of effective linear resolution.  I'd stop there are not try to
// push the angular resolution higher with a shorter D; with the 45 deg
// theta(max) at D = 1-17/32", we'd get a lovely DPI level of 341, but at
// the cost of getting pretty non-linear around the ends of the plunger
// travel.  Our math corrects for the non-linearity, but the more of that
// correction we need, the more sensitive the whole contraption becomes to
// getting the sensor positioning exactly right.  The closer we can stay to
// the linear approximation, the more tolerant we are of inexact sensor
// positioning.
// Supported sensors
//  * AEAT-6012-A06.  This is a magnetic absolute encoder with 12-bit
//    resolution.  It linearly encodes one full (360 degree) rotation in 
//    4096 increments, so each increment represents 360/4096 = .088 degrees.
// The base class doesn't actually care much about the sensor type; all it
// needs from the sensor is an angle reading represented on an arbitrary 
// linear scale.  ("Linear" in the angle, so that one increment represents
// a fixed number of degrees of arc.  The full scale can represent one full
// turn but doesn't have to, as long as the scale is linear over the range
// covered.)  To add new sensor types, you just need to add the code to
// interface to the physical sensor and return its reading on an arbitrary
// linear scale.


#include "FastInterruptIn.h"
#include "AEAT6012.h"

// The conversion from raw sensor reading to linear position involves a
// bunch of translations to different scales and unit systems.  To help
// keep things straight, let's give each scale a name:
// * "Raw" refers to the readings directly from the sensor.  These are
//   unsigned ints in the range 0..maxRawAngle, and represent angles in a
//   unit system where one increment equals 360/maxRawAngle degrees.  The
//   zero point is arbitrary, determined by the physical orientation
//   of the sensor.
// * "Biased" refers to angular units with a zero point equal to the
//   park position.  This uses the same unit size as the "raw" system, but
//   the zero point is adjusted so that 0 always means the park position.
//   Negative values are forward of the park position.  This scale is
//   also adjusted for wrapping, by ensuring that the value lies in the
//   range -(maximum forward excursion) to +(scale max - max fwd excursion).
//   Any values below or above the range are bumped up or down (respectively)
//   to wrap them back into the range.
// * "Linear" refers to the final linear results, in joystick units, on
//   the abstract integer scale from 0..65535 used by the generic plunger
//   base class.
class PlungerSensorRotary: public PlungerSensor
    PlungerSensorRotary(int maxRawAngle, float radiansPerSensorUnit) : 
        // start our sample timer with an arbitrary zero point of now
        // clear the timing statistics
        nReads = 0;
        totalReadTime = 0;
        // Pre-calculate the maximum forward excursion distance, in raw
        // units.  For our reference mechanical setup with "D" in a likely
        // range, theta(max) is always about 10 degrees higher than
        // theta(park).  10 degrees is about 1/36 of the overall circle,
        // which is the same as 1/36 of the sensor scale.  To be 
        // conservative, allow for about 3X that, so allow 1/12 of scale
        // as the maximum forward excursion.  For wrapping purposes, we'll
        // consider any reading outside of the range from -(excursion)
        // to +(maxRawAngle - excursion) to be wrapped.
        maxForwardExcursionRaw = maxRawAngle/12;
        // reset the calibration counters
        biasedMinObserved = biasedMaxObserved = 0;
    // Restore the saved calibration at startup
    virtual void restoreCalibration(Config &cfg)
        // only proceed if there's calibration data to retrieve
        if (
            // we store the raw park angle in raw0
            rawParkAngle =;
            // we store biased max angle in raw1
            biasedMax =;
            // Use the current sensor reading as the initial guess at the
            // park position.  The system is usually powered up with the
            // plunger at the neutral position, so this is a good guess in
            // most cases.  If the plunger has been calibrated, we'll restore
            // the better guess when we restore the configuration later on in
            // the initialization process.
            rawParkAngle = 0;

            // Set an initial wild guess at a range equal to +/-35 degrees.
            // Note that this is in the "biased" coordinate system - raw
            // units, but relative to the park angle.  The park angle is
            // about -25 degrees in this setup.
            biasedMax = (35 + 25) * maxRawAngle/360;        
        // recalculate the vertical angle
    // Begin calibration
    virtual void beginCalibration(Config &)
        // Calibration starts out with the plunger at the park position, so
        // we can take the current sensor reading to be the park position.
        rawParkAngle = 0;
        // Reset the observed calibration counters
        biasedMinObserved = biasedMaxObserved = 0;
    // End calibration
    virtual void endCalibration(Config &cfg)
        // apply the observed maximum angle
        biasedMax = biasedMaxObserved;
        // recalculate the vertical angle

        // save our raw configuration data = static_cast<uint16_t>(rawParkAngle); = static_cast<uint16_t>(biasedMax);
        // Refigure the range for the generic code = biasedAngleToLinear(biasedMinObserved); = biasedAngleToLinear(biasedMaxObserved); = biasedAngleToLinear(0);
    // figure the average scan time in microseconds
    virtual uint32_t getAvgScanTime() 
        return nReads == 0 ? 0 : static_cast<uint32_t>(totalReadTime / nReads);
    // read the sensor
    virtual bool readRaw(PlungerReading &r)
        // note the starting time for the reading
        uint32_t t0 = timer.read_us();
        // read the angular position
        int angle;
        if (!readSensor(angle))
            return false;

        // Refigure the angle relative to the raw park position.  This
        // is the "biased" angle.
        angle -= rawParkAngle;
        // Adjust for wrapping.
        // An angular sensor reports the position on a circular scale, for
        // obvious reasons, so there's some point along the circle where the
        // angle is zero.  One tick before that point reads as the maximum
        // angle on the scale, so we say that the scale "wraps" at that point.
        // To correct for this, we can look to the layout of the mechanical
        // setup to constrain the values.  Consider anything below the maximum
        // forward exclusion to be wrapped on the low side, and consider
        // anything outside of the complementary range on the high side to
        // be wrapped on the high side.
        if (angle < -maxForwardExcursionRaw)
            angle += maxRawAngle;
        else if (angle >= maxRawAngle - maxForwardExcursionRaw)
            angle -= maxRawAngle;
        // Note if this is the highest/lowest observed reading on the biased 
        // scale since the last calibration started.
        if (angle > biasedMaxObserved)
            biasedMaxObserved = angle;
        if (angle < biasedMinObserved)
            biasedMinObserved = angle;
        // figure the linear result
        r.pos = biasedAngleToLinear(angle);
        // Set the timestamp on the reading to right now
        uint32_t now = timer.read_us();
        r.t = now;
        // count the read statistics
        totalReadTime += now - t0;
        nReads += 1;        
        // success
        return true;
    // Read the underlying sensor - implemented by the hardware-specific
    // subclasses.  Returns true on success, false if the sensor can't
    // be read.  The angle is returned in raw sensor units.
    virtual bool readSensor(int &angle) = 0;

    // Convert a biased angle value to a linear reading
    int biasedAngleToLinear(int angle)
        // Translate to an angle relative to the vertical, in sensor units
        float theta = static_cast<float>(angle)*radiansPerSensorUnit - alpha;
        // Calculate the linear position relative to the vertical.  Zero
        // is right at the intersection of the vertical line from the
        // sensor rotation center to the plunger axis; positive numbers
        // are behind the vertical (more retracted).
        int linearPos = static_cast<int>(tanf(theta) * linearScaleFactor);
        // Finally, figure the offset.  The vertical is the halfway point
        // of the plunger motion, so we want to put it at half of the raw
        // scale of 0..65535.
        return linearPos + 32767;

    // Update the estimation of the vertical angle, based on the angle
    // between the park position and maximum retraction point.
    void updateAlpha()
        // See the comments at the top of the file for details on this
        // formula.  This figures the angle between the park position
        // and the vertical by applying the known constraints of the
        // mechanical setup: the known length of a standard plunger,
        // and the requirement that the rotation axis be placed at
        // roughly the midpoint of the plunger travel.
        const float C = 1.4848489f; // 1-17/32" / 1-1/32"
        float maxInRadians = static_cast<float>(biasedMax) * radiansPerSensorUnit;
        float T = tanf(maxInRadians);
        alpha = atanf((sqrtf(4*T*T*C + C*C + 2*C + 1) - C - 1)/(2*T*C));

        // While we're at it, figure the linear conversion factor.  Alpha
        // represents the angle from the park position to the midpoint,
        // which in the real world represents about 31/32", or just less
        // then 1/3 of the overall travel.  We want to normalize this to
        // the corresponding fraction of our 0..65535 abstract linear unit
        // system.  To avoid overflow, normalize to a slightly smaller
        // scale.
        const float safeMax = 60000.0f;
        const float alphaInLinearUnits = safeMax * .316327f; // 31/22" / 3-1/16"
        linearScaleFactor = static_cast<int>(alphaInLinearUnits / tanf(alpha));

    // Maximum raw angular reading from the sensor.  The sensor's readings
    // will always be on a scale from 0..maxRawAngle.
    int maxRawAngle;
    // Radians per sensor unit.  This is a constant for the sensor.
    float radiansPerSensorUnit;
    // Pre-calculated value of the maximum forward excursion, in raw units.
    int maxForwardExcursionRaw;
    // Raw reading at the park position.  We use this to handle "wrapping",
    // if the sensor's raw zero reading position is within the plunger travel
    // range.  All readings are taken to be within 
    int rawParkAngle;
    // Biased maximum angle.  This is the angle at the maximum retracted
    // position, in biased units (sensor units, relative to the park angle).
    int biasedMax;
    // Mininum and maximum angle observed since last calibration start, on 
    // the biased scale
    int biasedMinObserved;
    int biasedMaxObserved;
    // The "alpha" angle - the angle between the park position and the
    // vertical line between the rotation axis and the plunger.  This is
    // represented in radians.
    float alpha;
    // The linear scaling factor, applied in our trig calculation from
    // angle to linear position.  This corresponds to the distance from
    // the rotation center to the plunger rod, but since the linear result
    // is in abstract joystick units, this distance is likewise in abstract
    // units.  The value isn't chosen to correspond to any real-world 
    // distance units, but rather to yield a joystick result that takes
    // advantage of most of the available axis range, to minimize rounding
    // errors when converting between scales.
    float linearScaleFactor;

    // timer for input timestamps and read timing measurements
    Timer timer;
    // read timing statistics
    uint64_t totalReadTime;
    uint64_t nReads;
    // Keep track of when calibration is in progress.  The calibration
    // procedure is usually handled by the generic main loop code, but
    // in this case, we have to keep track of some of the raw sensor
    // data during calibration for our own internal purposes.
    bool calibrating;

// Specialization for the AEAT-601X sensors
template<int nDataBits> class PlungerSensorAEAT601X : public PlungerSensorRotary
    PlungerSensorAEAT601X(PinName csPin, PinName clkPin, PinName doPin) :
        PlungerSensorRotary((1 << nDataBits) - 1, 6.283185f/((1 << nDataBits) - 1)),
        aeat(csPin, clkPin, doPin) 
        // Make sure the sensor has had time to finish initializing.
        // Power-up time (tCF) from the data sheet is 20ms for the 12-bit
        // version, 50ms for the 10-bit version.
        wait_ms(nDataBits == 12 ? 20 :
            nDataBits == 10 ? 50 :

    // read the angle
    virtual bool readSensor(int &angle)
        angle = aeat.readAngle();
        return true;
    // physical sensor interface
    AEAT601X<nDataBits> aeat;