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.

--- a/main.cpp	Sat Feb 27 00:22:04 2016 +0000
+++ b/main.cpp	Sat Feb 27 06:41:17 2016 +0000
@@ -1,3 +1,47 @@
+// NEW PLUNGER PROCESSING 1 - 26 Feb 2016
+// This version takes advantage of the new, faster TSL1410R DMA processing
+// to implement better firing event detection.  This attempt works basically
+// like the old version, but uses the higher time resolution to detect firing
+// events more reliably.  The scheme here watches for accelerations (the old
+// TSL1410R code wasn't fast enough to do that).  We observed that a release
+// takes about 65ms from the maximum retraction point to crossing the zero
+// point.  Our 2.5ms snapshots allow us to see about 25 frames over this
+// span.  The first 5-10 frames will show the position moving forward, but
+// we don't see a clear acceleration trend in that first section.  After
+// that we see almost perfectly uniform acceleration for the rest of the
+// release until we cross the zero point.  "Almost" in that we often have
+// one or two frames where the velocity is just slightly lower than the
+// previous frame's.  I think this is probably imprecision in the sensor;
+// realistically, our time base is probably good to only +/- 1ms or so,
+// since the shutter time for each frame is about 2.3ms.  We assume that
+// each frame captures the midpoint time of the shutter span, but that's
+// a crude approximation; the scientifically right way to look at this is
+// that our snapshot times have an uncertainty on the order of the shutter
+// time.  Those error bars of course propagate into the velocity readings.
+// Fortunately, the true acceleration is high enough that it overwhelms
+// the error bars on almost every sample.  It appears to solve this
+// entirely if we simply skip a sample where we don't see acceleration
+// once we think a release has started - this takes our time between
+// samples up to about 5ms, at which point the acceleration does seem to
+// overwhelm the error bars 100% of the time.
+// I'm capturing a snapshot of this implementation because I'm going to
+// try something different.  It would be much simpler if we could put our
+// readings on a slight time delay, and identify firing events
+// retrospectively when we actually cross the zero point.  I'm going to
+// experiment first with a time delay to see what the maximum acceptable
+// delay time is.  I expect that I can go up to about 30ms without it
+// becoming noticeable, but I need to try it out.  If we can go up to
+// 70ms, we can capture firing events perfectly because we can delay
+// reports long enough to have an entire firing event in history before
+// we report anything.  That will let us fix up the history to report an
+// idealized firing event to VP every time, with no false positives.
+// But I suspect a 70ms delay is going to be way too noticeable.  If
+// a 30ms delay works, I think we can still do a pretty good job - that
+// gets us about halfway into a release motion, at which point it's
+// pretty certain that it's really a release.
 /* Copyright 2014, 2015 M J Roberts, MIT License
 * Permission is hereby granted, free of charge, to any person obtaining a copy of this software
@@ -2319,33 +2363,9 @@
         // no history yet
         histIdx = 0;
-        histR = 0;
         // not in calibration mode
-        cal = false;   
-    }
-    // prime the history
-    void prime()
-    {
-        // fill the initial history buffer, timing out if it takes too long
-        plungerSensor->read(prv);
-        Timer t;
-        t.start();
-        const uint32_t timeout = 1000000UL;
-        for (int i = 0 ; i < countof(hist) && t.read_us() < timeout ; ++i)
-        {
-            // take a new reading that's at least 2ms newer than the last
-            PlungerReading r;
-            while (t.read_us() < timeout)
-            {
-                if (plungerSensor->read(r) && uint32_t(r.t - prv.t) > 2000UL)
-                    break;
-            }
-            addHist(r);
-            prv = r;
-        }
-        histR = 0;
+        cal = false;
     // Collect a reading from the plunger sensor.  The main loop calls
@@ -2374,17 +2394,12 @@
                 // sensor position as the joystick value, adjusted to the
                 // JOYMAX scale.
                 z = int16_t((long(r.pos) * JOYMAX)/65535);
+                return;
-            else
-            {
-                // bounds-check the calibration data
-                checkCalBounds(r.pos);
-                // calibrate and rescale the value
-                r.pos = int(
-                    (long(r.pos - * JOYMAX)
-                    / ( -;
-            }
+            // Pull the last two readings from the history
+            const PlungerReading &prv = nthHist(0);
+            const PlungerReading &prv2 = nthHist(1);
             // If the new reading is within 2ms of the previous reading,
             // ignore it.  We require a minimum time between samples to
@@ -2397,46 +2412,225 @@
             if (uint32_t(r.t - prv.t) < 2000UL)
-            // Save it as the previous sample
-            prv = r;
+            // bounds-check the calibration data
+            checkCalBounds(r.pos);
+            // calibrate and rescale the value
+            r.pos = int(
+                (long(r.pos - * JOYMAX)
+                / ( -;
+            // Calculate the velocity from the second-to-last reading
+            // to here, in joystick distance units per microsecond.
+            // Note that we use the second-to-last reading rather than
+            // the very last reading to give ourselves a little longer
+            // time base.  The time base is so short between consecutive
+            // readings that the error bars in the position would be too
+            // large.
+            //
+            // For reference, the physical plunger velocity ranges up
+            // to about 100,000 joystick distance units/sec.  This is 
+            // based on empirical measurements.  The typical time for 
+            // a real plunger to travel the full distance when released 
+            // from full retraction is about 85ms, so the average velocity 
+            // covering this distance is about 56,000 units/sec.  The 
+            // peak is probably about twice that.  In real-world units, 
+            // this translates to an average speed of about .75 m/s and 
+            // a peak of about 1.5 m/s.
+            //
+            // Note that we actually calculate the value here in units
+            // per *microsecond* - the discussion above is in terms of
+            // units/sec because that's more on a human scale.  Our
+            // choice of internal units here really isn't important,
+            // since we only use the velocity for comparison purposes,
+            // to detect acceleration trends.  We therefore save ourselves
+            // a little CPU time by using the natural units of our inputs.
+            float v = float(r.pos - prv2.pos)/float(r.t - prv2.t);
+            // presume we'll report the latest instantaneous reading
+            z = r.pos;
+            vz = v;
-            // Add it to our history
-            addHist(r);
+            // Check firing events
+            switch (firing)
+            {
+            case 0:
+                // Default state - not in a firing event.  
+                // If we have forward motion from a position that's retracted 
+                // beyond a threshold, enter phase 1.  If we're not pulled back
+                // far enough, don't bother with this, as a release wouldn't
+                // be strong enough to require the synthetic firing treatment.
+                if (v < 0 && r.pos > JOYMAX/6)
+                {
+                    // enter phase 1
+                    firingMode(1);
+                    // we don't have a freeze position yet, but note the start time
+                    f1.pos = 0;
+                    f1.t = r.t;
+                    // Figure the barrel spring "bounce" position in case we complete 
+                    // the firing event.  This is the amount that the forward momentum
+                    // of the plunger will compress the barrel spring at the peak of
+                    // the forward travel during the release.  Assume that this is
+                    // linearly proportional to the starting retraction distance.  
+                    // The barrel spring is about 1/6 the length of the main spring, 
+                    // so figure it compresses by 1/6 the distance.  (This is overly
+                    // simplistic and inaccurate, but it seems to give perfectly good
+                    // visual results, and that's all it's for.)
+                    f2.pos = -r.pos/6;
+                }
+                break;
+            case 1:
+                // Phase 1 - acceleration.  If we cross the zero point, trigger
+                // the firing event.  Otherwise, continue monitoring as long as we
+                // see acceleration in the forward direction.
+                if (r.pos <= 0)
+                {
+                    // switch to the synthetic firing mode
+                    firingMode(2);
+                    z = f2.pos;
+                    // note the start time for the firing phase
+                    f2.t = r.t;
+                }
+                else if (v < vprv2)
+                {
+                    // We're still accelerating, and we haven't crossed the zero
+                    // point yet - stay in phase 1.  (Note that forward motion is
+                    // negative velocity, so accelerating means that the new 
+                    // velocity is more negative than the previous one, which
+                    // is to say numerically less than - that's why the test
+                    // for acceleration is the seemingly backwards 'v < vprv'.)
+                    // If we've been accelerating for at least 20ms, we're probably
+                    // really doing a release.  Jump back to the recent local
+                    // maximum where the release *really* started.  This is always
+                    // a bit before we started seeing sustained accleration, because
+                    // the plunger motion for the first few milliseconds is too slow
+                    // for our sensor precision to reliably detect acceleration.
+                    if (f1.pos != 0)
+                    {
+                        // we have a reset point - freeze there
+                        z = f1.pos;
+                    }
+                    else if (uint32_t(r.t - f1.t) >= 20000UL)
+                    {
+                        // it's been long enough - set a reset point.
+                        f1.pos = z = histLocalMax(r.t, 50000UL);
+                    }
+                }
+                else
+                {
+                    // We're not accelerating.  Cancel the firing event.
+                    firingMode(0);
+                }
+                break;
+            case 2:
+                // Phase 2 - start of synthetic firing event.  Report the fake
+                // bounce for 25ms.  VP polls the joystick about every 10ms, so 
+                // this should be enough time to guarantee that VP sees this
+                // report at least once.
+                if (uint32_t(r.t - f2.t) < 25000UL)
+                {
+                    // report the bounce position
+                    z = f2.pos;
+                }
+                else
+                {
+                    // it's been long enough - switch to phase 3, where we
+                    // report the park position until the real plunger comes
+                    // to rest
+                    firingMode(3);
+                    z = 0;
+                    // set the start of the "stability window" to the rest position
+                    f3s.t = r.t;
+                    f3s.pos = 0;
+                    // set the start of the "retraction window" to the actual position
+                    f3r = r;
+                }
+                break;
+            case 3:
+                // Phase 3 - in synthetic firing event.  Report the park position
+                // until the plunger position stabilizes.  Left to its own devices, 
+                // the plunger will usualy bounce off the barrel spring several 
+                // times before coming to rest, so we'll see oscillating motion
+                // for a second or two.  In the simplest case, we can aimply wait
+                // for the plunger to stop moving for a short time.  However, the
+                // player might intervene by pulling the plunger back again, so
+                // watch for that motion as well.  If we're just bouncing freely,
+                // we'll see the direction change frequently.  If the player is
+                // moving the plunger manually, the direction will be constant
+                // for longer.
+                if (v >= 0)
+                {
+                    // We're moving back (or standing still).  If this has been
+                    // going on for a while, the user must have taken control.
+                    if (uint32_t(r.t - f3r.t) > 65000UL)
+                    {
+                        // user has taken control - cancel firing mode
+                        firingMode(0);
+                        break;
+                    }
+                }
+                else
+                {
+                    // forward motion - reset retraction window
+                    f3r.t = r.t;
+                }
+                // check if we've come to rest, or close enough
+                if (abs(r.pos - f3s.pos) < 200)
+                {
+                    // It's within an eighth inch of the last starting point. 
+                    // If it's been here for 30ms, consider it stable.
+                    if (uint32_t(r.t - f3s.t) > 30000UL)
+                    {
+                        // we're done with the firing event
+                        firingMode(0);
+                    }
+                    else
+                    {
+                        // it's close to the last position but hasn't been
+                        // here long enough; stay in firing mode and continue
+                        // to report the park position
+                        z = 0;
+                    }
+                }
+                else
+                {
+                    // It's not close enough to the last starting point, so use
+                    // this as a new starting point, and stay in firing mode.
+                    f3s = r;
+                    z = 0;
+                }
+                break;
+            }
+            // save the velocity reading for next time
+            vprv2 = vprv;
+            vprv = v;
+            // add the new reading to the history
+            hist[histIdx++] = r;
+            histIdx %= countof(hist);
     // Get the current value to report through the joystick interface
-    int16_t getPosition()
-    {
-        // advance the read pointer until it's not too old
-        const uint32_t dtmax = 100000UL;
-        for (;;)
-        {
-            // if this one isn't too old, use it
-            if (uint32_t(prv.t - hist[histR].t) <= dtmax)
-                break;
-            // It's too old.  Figure the next read index.
-            int i = (histR + 1) % countof(hist);
-            // if discarding this one would empty the history, keep
-            // it and stop here
-            if (i == histIdx)
-                break;
-            // discard this item by advancing the read pointer
-            histR = i;
-        }
-        // return the position at the current read index
-        return hist[histR].pos;
-    }
+    int16_t getPosition() const { return z; }
     // Get the current velocity (joystick distance units per microsecond)
     float getVelocity() const { return vz; }
     // get the timestamp of the current joystick report (microseconds)
-    uint32_t getTimestamp() const { return prv.t; }
+    uint32_t getTimestamp() const { return nthHist(0).t; }
     // Set calibration mode on or off
     void calMode(bool f) 
@@ -2453,19 +2647,6 @@
     bool isFiring() { return firing > 3; }
-    // add a history entry
-    inline void addHist(PlungerReading &r)
-    {
-        // if we're about to overwrite the item at the read pointer,
-        // advance the read pointer
-        if (histIdx == histR)
-            histR = (histR + 1) % countof(hist);
-        // add the new entry
-        hist[histIdx++] = r;
-        histIdx %= countof(hist);
-    }
     // set a firing mode
     inline void firingMode(int m) 
@@ -2559,11 +2740,8 @@
-    // Previous reading
-    PlungerReading prv;
-    // velocity at previous reading
-    float vprv;
+    // velocity at previous reading, and the one before that
+    float vprv, vprv2;
     // Circular buffer of recent readings.  We keep a short history
     // of readings to analyze during firing events.  We can only identify
@@ -2572,11 +2750,22 @@
     // exactly when it started.  We throttle our readings to no more
     // than one every 2ms, so we have at least N*2ms of history in this
     // array.
-    PlungerReading hist[50];
+    PlungerReading hist[25];
     int histIdx;
-    // history read index
-    int histR;
+    // get the nth history item (0=last, 1=2nd to last, etc)
+    const PlungerReading &nthHist(int n) const
+    {
+        // histIdx-1 is the last written; go from there
+        n = histIdx - 1 - n;
+        // adjust for wrapping
+        if (n < 0)
+            n += countof(hist);
+        // return the item
+        return hist[n];
+    }
     // Firing event state.
@@ -3469,9 +3658,6 @@
     // initialize the plunger sensor
-    // prime the plunger reader
     // set up the ZB Launch Ball monitor
     ZBLaunchBall zbLaunchBall;
@@ -3622,13 +3808,11 @@
         // flag:  did we successfully send a joystick report on this round?
         bool jsOK = false;
-        // If it's been long enough since our last USB status report,
-        // send the new report.  We throttle the report rate because
-        // it can overwhelm the PC side if we report too frequently.
-        // VP only wants to sync with the real world in 10ms intervals,
-        // so reporting more frequently creates I/O overhead without 
-        // doing anything to improve the simulation.
-        if (cfg.joystickEnabled /* $$$ && jsReportTimer.read_us() > 10000 */)
+        // If it's been long enough since our last USB status report, send
+        // the new report.  VP only polls for input in 10ms intervals, so
+        // there's no benefit in sending reports more frequently than this.
+        // More frequent reporting would only add USB I/O overhead.
+        if (cfg.joystickEnabled && jsReportTimer.read_us() > 10000UL)
             // read the accelerometer
             int xa, ya;