Initial report by Min Lee, April, 11, 2006

QT301 Capacitance to Analog Converter Data Report by Min Lee; Spring 2006 Min's ITP blog

QT113, 1 channel touch sensor, Datasheet Study

Touch lighting up the QT113

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Analog QT301

Unlike the QT113, the one-channel, touch sensor, the QT301 works off of the capacitance and outputs an analog signal. It has a PWM pin as oppsed to a digital OUT pin on the sensor.

Quantum Research's QT300 family QProx programmable capacitive ICs are suitable for touch, proximity, fluid, and material sensing.

What is it? - The QT301 QProx programmable capacitive IC is suitable for fluid, and material sensing. It can project sense fields through up to 100mm (4) of insulation or air. It is an 8-pin device available in SOIC or DIP. - Its only output is raw, unprocessed data in filterable PWM form that can be translated into an analog voltage. - PWM signal is a eight bits in resolution.

How is it different from other Touch Qprox sensors? - Rescaleable PWM: PWM is set by two inputs that control the starting and the end point of the range. (Calibration pins) The PWM range can be optimized for the zone of interest for the user. - Sync input is present to avoid external noise sources. - Sensor's Internal Operation : QT301 has an EEPROM to store the two calibration points.

Basic Operations

- In the circuit above, R1, R2, R3 are all 10K resistors and the C1 is 100nF. - power-up delay of 300ms.

Cs/Cx Dependency - The signal value depends directly on the Cs and Cx, where the Cs is the fixed capacitor, Cx is the unknown. - The two values influence the sensitivity, resolution and response time of the electrode. - Sensitivity and resolution are also a function of the size, shape and composition of the electrode.

PWM Output - output is 100KHZ +- 7% square wave - may not be 100% linear with changes in Cx - during CAL, PWM output value is locked with the value just before the CAL process

Calibration - CAL PINs are inputs used to trigger CAL process on the upper and lower Cx - pins go through a pull down resistor to prevent damage (Note: NEVER BE driven low. will short circuit the chip) - calibrated to have an effective properly scaled PWM output - CAL_DN should be used to calibrate when the signal of the electrode is at its lowest - CAL_UP should be used to calibrate when the signal of the electrode is at its max - does not matter whether CAL_DN or CAL_UP are applied first - after calibration, i can be calibrated again for adjustment

Like in the QT113, I found out that shielding the electrode with a ground around it gave it more focus for the part that was sensing.

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For my Living Art Project, I am using about 80 LEDs per candy jar to add movement and light to the LEDs. Hence, I attempted at trying to get as many LEDs to work off the PWM QT301 PIN. I had to go through a TIP120 transistor to be able to power all the 54 LEDs all at once to PWM according to the electrode off of the QT301.

movie demo