SoftPot multitouch (up to 2 positions) and gap measurement library for Arduino.
Two test resistors are required in order to make the circuit working properly. They need to be chosen specifically for the application. The resistance of the test resistors needs to be large enough so that the SoftPot will not overheat when one or both of the ends are touched (creates a short circuit between the center pin and one or two side pins) and small enough so that the voltage difference measured from SoftPot is large enough to calculate the position.
If in doubt and the total resistance of your SoftPot is 10Kohm or 20Kohm (they are the most common type and sold on SparkFun, Adafruit, Digikey, Mouser, etc. for a small quantity), use test resistors with resistance of 10Kohm.
WARNING: Bad choice of test resistors can cause inaccurate measurement or permanent damage to the SoftPot/Arduino.
Connect your SoftPot and test resistors to the Arduino as follows:
Vref is the reference voltage of the analog pins of your Arduino (5V pin for
5V Arduino boards and 3.3V/3V3 for 3.3V Arduino boards).
ADC_LEFT and ADC_RIGHT are the analog pins of your choice.
R1 and R2 are the test resistors and RV1 is the SoftPot.
To use the library, you must initialize it first with
SoftPotMagic.begin(<left_pin>, <right_pin>) in the setup() function where
<left_pin> and <right_pin> are the analog pins of your choice.
A calibration also needs to be performed either by calling
SoftPotMagic.autoCalibLeft() when you
press and hold the left end of the SoftPot and SoftPotMagic.autoCalibRight()
for the right end, or by telling the resistance of your test resistors and the
total resistance of your SoftPot to the library by calling
SoftPotMagic.setCalib(<RTestL>, <RTestR>, <RSoftPot>, <ADCMax>). (ADCMax is
the maximum value analogRead() can return (typically 1023 for Arduino)).
The calibration data can be backed up on a persistent storage (e.g. EEPROM).
You can get the pointer of the calibration data by using
calib_t *calib = SoftPotMagic.getCalib() and save it. Use
SoftPotMagic.setCalib(calib) to load calibration data to the library.
If your SoftPot does not report POS_FLOAT when not touched, you might also
want to adjust the ADC zero level by using the SoftPotMagic.autoCalibZero()
when not touching the SoftPot. The value obtained by this call will be stored
in the calibration data and can be fetched using getCalib(). You can also then
call SoftPotMagic.autoCalibZero(false) multiple times to get a maximum value
of ADC readings where it should be zero.
In addition to the calibration, you need to also specify the largest size of a
single point touch via SoftPotMagic.setMinGapRatio(), which is represented as
a float number between 0.0 and 1.0. You can calculate this value based on how
long your SoftPot is and the rough size of the thing that you use to touch the
SoftPot (e.g. finger, stylus, wiper, etc.). You can also read it back
using SoftPotMagic.getMinGapRatio() so that it can be stored in some permanent
storage (such as EEPROM).
Use SoftPotMagic.update() to get the latest update for the positions (it
should be called periodically). You can then use SoftPotMagic.pos1() and
SoftPotMagic.pos2() to get the positions. In the case of gap
measurement, use SoftPotMagic.gapCenter() for the center position of gap and
SoftPotMagic.gapSize() for the distance of it.
The returned value of these functions range from 0 (POS_MIN) to 254
(POS_MAX), 255 or POS_FLOAT is returned if no touch/gap was detected.
Refer to the example for more information.
- Ribbon controller that supports 2 simultaneous voices
- Resistive slider that supports basic gestures (pinch-in, pinch-out, two-finger drag, etc.)
- Slider controller of a certain game
LGPLv3+
adzy31 for his YouTube video that makes me realize the possibility of doing 2 position touch sensing on a SoftPot.