Touch Sensor Module

Description

The Touch Sensor Module utilizes a floating lead on a Darlington transistor to detect a touch.

PACKAGE INCLUDES:

• Touch Sensor Module

KEY FEATURES OF TOUCH SENSOR MODULE:

• Uses floating lead of Darlington transistor to detect the touch
• Digital and analog outputs
• 3.3 and 5V compatible

The touch sensor module utilizes a Darlington transistor as it’s sensing element.  The base lead of the transistor is left floating in air and it will pickup weak electrical signals from the human body which are then amplified and serves as the touch indication.

There are 2 LEDs on-board.  A red LED lights when power is applied.  A green or red LED lights when a touch is detected.

Theory of Operation

The human body is somewhat conductive and the home is filled with 60Hz electromagnetic energy from the electrical system such as from lights, which the body picks up.  When a finger is placed on the base lead, the energy is passed from the body to the transistor.

The weak signal is amplified by the transistor and output on both an Analog output and a Digital output pin after it goes though a comparator circuit.

The analog output is normally HIGH and pulses LOW at a 60Hz rate when the sensor is touched. That is because the 60Hz is coupling from the body to the transistor.

The digital output is the opposite polarity and is normally LOW and pulses HIGH when it is touched.  The digital output is the output of an LM393 comparator IC, so the output has less noise on the signal.

Scope captures of both the analog and digital outputs are shown below.

Analog Output with Finger Detected

Digital Output with Finger Detected

Note:  The potentiometer on the board does not appear to affect the sensitivity or shape of the outputs in any noticeable way.  Perhaps because the waveform is already more or less a square-shape.

Module Connections

There is a 4-pin header on the assembly for making connections.

1 x 4 Header 

• A0 = Analog output, connects to analog or digital input on uC
• G/GND  = Ground
• ‘+’ = Vcc (3.3 – 5V)
• D0 = Digital output, connects to digital input on uC

OUR EVALUATION RESULTS:

These modules are useful for evaluating basic touch applications.  The Analog output is probably best treated as a normally HIGH digital input rather than an analog input.

BEFORE THEY ARE SHIPPED, THESE MODULES ARE:

• Inspected
• Basic outputs verified
• Packaged in a resealable ESD bag for protection and easy storage.

Notes: 

1. None

Technical Specifications