Mike R / Mbed 2 deprecated Pinscape_Controller

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Dependencies:   USBDevice mbed FastAnalogIn FastIO FastPWM SimpleDMA

potSensor.h@43:7a6364d82a41, 2016-02-06 (annotated)

Committer:
mjr
Date:
Sat Feb 06 20:21:48 2016 +0000
Revision:
43:7a6364d82a41
Parent:
35:e959ffba78fd
Child:
44:b5ac89b9cd5d
Before floating point plunger ranging

Who changed what in which revision?

UserRevisionLine numberNew contents of line
mjr 17:ab3cec0c8bf4 1 // Potentiometer plunger sensor
mjr 17:ab3cec0c8bf4 2 //
mjr 17:ab3cec0c8bf4 3 // This file implements our generic plunger sensor interface for a
mjr 43:7a6364d82a41 4 // potentiometer. The potentiometer resistance must be linear in
mjr 43:7a6364d82a41 5 // position. To connect physically, wire the fixed ends of the
mjr 43:7a6364d82a41 6 // potentiometer to +3.3V and GND (respectively), and connect the
mjr 43:7a6364d82a41 7 // wiper to an ADC-capable GPIO pin on the KL25Z. The wiper voltage
mjr 43:7a6364d82a41 8 // that we read on the ADC will vary linearly with the wiper position.
mjr 43:7a6364d82a41 9 // Mechanically attach the wiper to the plunger so that the wiper moves
mjr 43:7a6364d82a41 10 // in lock step with the plunger.
mjr 43:7a6364d82a41 11 //
mjr 43:7a6364d82a41 12 // Although this class is nominally for potentiometers, it will also
mjr 43:7a6364d82a41 13 // work with any other type of sensor that provides a single analog
mjr 43:7a6364d82a41 14 // voltage level that maps linearly to the position, such as an LVDT.
mjr 17:ab3cec0c8bf4 15
mjr 17:ab3cec0c8bf4 16
mjr 35:e959ffba78fd 17 class PlungerSensorPot: public PlungerSensor
mjr 17:ab3cec0c8bf4 18 {
mjr 17:ab3cec0c8bf4 19 public:
mjr 35:e959ffba78fd 20 PlungerSensorPot(PinName ao) : pot(ao)
mjr 17:ab3cec0c8bf4 21 {
mjr 17:ab3cec0c8bf4 22 }
mjr 17:ab3cec0c8bf4 23
mjr 35:e959ffba78fd 24 virtual void init()
mjr 17:ab3cec0c8bf4 25 {
mjr 35:e959ffba78fd 26 // The potentiometer doesn't have pixels, but we still need an
mjr 35:e959ffba78fd 27 // integer range for normalizing our digitized voltage level values.
mjr 35:e959ffba78fd 28 // The number here is fairly arbitrary; the higher it is, the finer
mjr 35:e959ffba78fd 29 // the digitized steps. A 40" 1080p HDTV has about 55 pixels per inch
mjr 35:e959ffba78fd 30 // on its physical display, so if the on-screen plunger is displayed
mjr 35:e959ffba78fd 31 // at roughly the true physical size, it's about 3" on screen or about
mjr 35:e959ffba78fd 32 // 165 pixels. So the minimum quantization size here should be about
mjr 35:e959ffba78fd 33 // the same. For the pot sensor, this is just a scaling factor,
mjr 35:e959ffba78fd 34 // so higher values don't cost us anything (unlike the CCD, where the
mjr 35:e959ffba78fd 35 // read time is proportional to the number of pixels we sample).
mjr 35:e959ffba78fd 36 npix = 4096;
mjr 17:ab3cec0c8bf4 37 }
mjr 17:ab3cec0c8bf4 38
mjr 35:e959ffba78fd 39 virtual bool highResScan(int &pos)
mjr 17:ab3cec0c8bf4 40 {
mjr 23:14f8c5004cd0 41 // Take a few readings and use the average, to reduce the effect
mjr 23:14f8c5004cd0 42 // of analog voltage fluctuations. The voltage range on the ADC
mjr 23:14f8c5004cd0 43 // is 0-3.3V, and empirically it looks like we can expect random
mjr 23:14f8c5004cd0 44 // voltage fluctuations of up to 50 mV, which is about 1.5% of
mjr 23:14f8c5004cd0 45 // the overall range. We try to quantize at about the mm level
mjr 23:14f8c5004cd0 46 // (in terms of the plunger motion range), which is about 1%.
mjr 23:14f8c5004cd0 47 // So 1.5% noise is big enough to be visible in the joystick
mjr 23:14f8c5004cd0 48 // reports. Averaging several readings should help smooth out
mjr 23:14f8c5004cd0 49 // random noise in the readings.
mjr 23:14f8c5004cd0 50 pos = int((pot.read() + pot.read() + pot.read())/3.0 * npix);
mjr 17:ab3cec0c8bf4 51 return true;
mjr 17:ab3cec0c8bf4 52 }
mjr 17:ab3cec0c8bf4 53
mjr 35:e959ffba78fd 54 virtual bool lowResScan(int &pos)
mjr 23:14f8c5004cd0 55 {
mjr 23:14f8c5004cd0 56 // Use an average of several readings. Note that even though this
mjr 23:14f8c5004cd0 57 // is nominally a "low res" scan, we can still afford to take an
mjr 43:7a6364d82a41 58 // average. The point of the low res interface is to speed things
mjr 43:7a6364d82a41 59 // up for the image sensor types, which have a large number of
mjr 43:7a6364d82a41 60 // analog samples to read. In our case, we only have the one
mjr 43:7a6364d82a41 61 // input to sample, so our normal scan is already so fast that
mjr 43:7a6364d82a41 62 // there's no need to do anything different here.
mjr 35:e959ffba78fd 63 pos = int((pot.read() + pot.read() + pot.read())/3.0 * npix);
mjr 35:e959ffba78fd 64 return true;
mjr 23:14f8c5004cd0 65 }
mjr 23:14f8c5004cd0 66
mjr 17:ab3cec0c8bf4 67 private:
mjr 23:14f8c5004cd0 68 AnalogIn pot;
mjr 17:ab3cec0c8bf4 69 };