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work in progress
Dependencies: FastAnalogIn FastIO USBDevice mbed FastPWM SimpleDMA
Fork of Pinscape_Controller by
Diff: ccdSensor.h
- Revision:
- 17:ab3cec0c8bf4
- Child:
- 18:5e890ebd0023
--- /dev/null Thu Jan 01 00:00:00 1970 +0000 +++ b/ccdSensor.h Fri Feb 27 04:14:04 2015 +0000 @@ -0,0 +1,187 @@ +// CCD plunger sensor +// +// This file implements our generic plunger sensor interface for the +// TAOS TSL1410R CCD array sensor. + + + +// Number of pixels we read from the CCD on each frame. This can be +// less than the actual sensor size if desired; if so, we'll read every +// nth pixel. E.g., with a 1280-pixel physical sensor, if npix is 320, +// we'll read every 4th pixel. Reading a pixel is fairly time-consuming, +// because it requires waiting for the pixel's electric charge to +// stabilize on the CCD output, for the charge to transfer to the KL25Z +// input, and then for the KL25Z analog voltage sampler to get a stable +// reading. This all takes about 15us per pixel, which adds up to +// a relatively long time in such a large array. However, we can skip +// a pixel without waiting for all of that charge stabilization time, +// so we can get higher frame rates by only sampling a subset of the +// pixels. The array is so dense (400dpi) that we can still get +// excellent resolution by reading a fraction of the total pixels. +// +// Empirically, 160 pixels seems to be the point of diminishing returns +// for resolution - going higher will only improve the apparent smoothness +// slightly, if at all. 160 pixels gives us 50dpi on the sensor, which +// is roughly the same as the physical pixel pitch of a typical cabinet +// playfield monitor. (1080p HDTV displayed 1920x1080 pixels, and a 40" +// TV is about 35" wide, so the dot pitch is about 55dpi across the width +// of the TV. If on-screen plunger is displayed at roughly the true +// physical size, it's about 3" on the screen, or about 165 pixels. So at +// 160 pixels on the sensor, one pixel on the sensor translates to almost +// exactly one on-screen pixel on the TV, which makes the animated motion +// on-screen about as smooth as it can be. Looked at another way, 50dpi +// means that we're measuring the physical shooter rod position in about +// half-millimeter increments, which is probably better than I can +// discern by feel or sight. +const int npix = 160; + + +class PlungerSensor +{ +public: + PlungerSensor() : ccd(CCD_SO_PIN) + { + } + + // initialize + void init() + { + // flush any random power-on values from the CCD's integration + // capacitors, and start the first integration cycle + ccd.clear(); + } + + // Perform a low-res scan of the sensor. + int lowResScan() + { + + // read the pixels at low resolution + const int nlpix = 32; + uint16_t pix[nlpix]; + ccd.read(pix, nlpix); + + // determine which end is brighter + uint16_t p1 = pix[0]; + uint16_t p2 = pix[nlpix-1]; + int si = 1, di = 1; + if (p1 < p2) + si = nlpix, di = -1; + + // figure the shadow edge threshold - just use the midpoint + // of the levels at the bright and dark ends + uint16_t shadow = uint16_t((long(p1) + long(p2))/2); + + // find the current tip position + for (int n = 0 ; n < nlpix ; ++n, si += di) + { + // check to see if we found the shadow + if (pix[si] <= shadow) + { + // got it - normalize it to normal 'npix' resolution and + // return the result + return n*npix/nlpix; + } + } + + // didn't find a shadow - assume the whole array is in shadow (so + // the edge is at the zero pixel point) + return 0; + } + + // Perform a high-res scan of the sensor. + bool highResScan(int &pos) + { + // read the array + ccd.read(pix, npix, ccdReadCB, 0, 3); + + // get the average brightness at each end of the sensor + long avg1 = (long(pix[0]) + long(pix[1]) + long(pix[2]) + long(pix[3]) + long(pix[4]))/5; + long avg2 = (long(pix[npix-1]) + long(pix[npix-2]) + long(pix[npix-3]) + long(pix[npix-4]) + long(pix[npix-5]))/5; + + // Work from the bright end to the dark end. VP interprets the + // Z axis value as the amount the plunger is pulled: zero is the + // rest position, and the axis maximum is fully pulled. So we + // essentially want to report how much of the sensor is lit, + // since this increases as the plunger is pulled back. + int si = 1, di = 1; + long avgHi = avg1; + if (avg1 < avg2) + si = npix - 2, di = -1, avgHi = avg2; + + // Figure the shadow threshold. In practice, the portion of the + // sensor that's not in shadow has all pixels consistently near + // saturation; the first drop in brightness is pretty reliably the + // start of the shadow. So set the threshold level to be closer + // to the bright end's brightness level, so that we detect the leading + // edge if the shadow isn't perfectly sharp. Use the point 1/3 of + // the way down from the high top the low side, so: + // + // threshold = lo + (hi - lo)*2/3 + // = lo + hi*2/3 - lo*2/3 + // = lo - lo*2/3 + hi*2/3 + // = lo*1/3 + hi*2/3 + // = (lo + hi*2)/3 + // + // Then multiply the whole thing by 3 to factor out the averaging + // of each three adjacent pixels that we do in the loop (to save a + // little time on a mulitply on each loop): + // + // threshold' = lo + 2*hi + // + // Now, 'lo' is always one of avg1 or avg2, and 'hi' is the other + // one, so we can rewrite this as hi + avg1 + avg2. We also already + // pulled out 'hi' as avgHi, so we finally come to the final + // simplified expression: + long midpt = avg1 + avg2 + avgHi; + + // If we have enough contrast, proceed with the scan. + // + // If the bright end and dark end don't differ by enough, skip this + // reading entirely. Either we have an overexposed or underexposed frame, + // or the sensor is misaligned and is either fully in or out of shadow + // (it's supposed to be mounted such that the edge of the shadow always + // falls within the sensor, for any possible plunger position). + if (labs(avg1 - avg2) > 0x1000) + { + uint16_t *pixp = pix + si; + for (int n = 1 ; n < npix - 1 ; ++n, pixp += di) + { + // if we've crossed the midpoint, report this position + if (long(pixp[-1]) + long(pixp[0]) + long(pixp[1]) < midpt) + { + // note the new position + pos = n; + return true; + } + } + } + + // we didn't find a shadow - return no reading + return false; + } + + // send an exposure report to the joystick interface + void sendExposureReport(USBJoystick &js) + { + // send reports for all pixels + int idx = 0; + while (idx < npix) + js.updateExposure(idx, npix, pix); + + // The pixel dump requires many USB reports, since each report + // can only send a few pixel values. An integration cycle has + // been running all this time, since each read starts a new + // cycle. Our timing is longer than usual on this round, so + // the integration won't be comparable to a normal cycle. Throw + // this one away by doing a read now, and throwing it away - that + // will get the timing of the *next* cycle roughly back to normal. + ccd.read(pix, npix); + } + +private: + // pixel buffer + uint16_t pix[npix]; + + // the low-level interface to the CCD hardware + TSL1410R<CCD_SI_PIN, CCD_CLOCK_PIN> ccd; +};