Sound Platform 2 - 触摸控制按键

Customer Feedback

I purchased two sound freaq units some time ago at Target. Use the one for some time with no issues and loved it and raised about it so much that I recommended it and purchased another one as a backup for the future. At some point, speaker did not want to turn on and when it did it basically went haywire where none of the controls were functionable and it did whatever it wanted to to the point that it now turns on and off depending on where I plug it in or sometimes not at all is where I'm at. Frustrated at this one I went and opened up my brand new one again as a backup because I love the item so much and, low and behold this unit has never been used and is doing exactly what my original one is doing. Now I am stuck with two speakers which do not turn on or off and are not functionable, but I have to say this has have to the best speaker that I ever owned and really wish you could help me out with figuring the issues with the units. Any help would be much appreciated and hope to hear from you?

—Joseph Petrizio

The SFQ-06 buttons are all touch sensory based, so there is no such thing as a deformed or depressed button. There are no physical pins to create on/off conditions as in a dome switch type of circuit. Instead, the on/off state of a touch sensory button is simulated by the change in capacitance value with or without a user's finger touch.

This is the simplified working principle of using an open capacitor as a touch sensor.

The button PCBA board of SFQ-06 is attached to the top cover with double-sided adhesive tape just below the plastic housing. It should remain in place and maintain its original position for correct operation. If the double-sided tape is out of work and the button board is moved out of position, the capacitance resulting from the finger touch will deviate and generate inconsistent signals to the CPU. This will cause the speaker to behave erratically, as Joseph describes below. Judging from his account, I'm afraid it's very likely that the circuit board has already come loose and moved out of position, causing inconsistent signal mapping on both the old and new units.

There will be two challenges up ahead should Joseph considers saving the two units

1. How to open the plastic housing - it’s quite complicated and takes sometime for our engineers to figure out
2. Take off the button board, Replace the double side adhesive, Put it back and Store its original position.

What is a Touch Sensor?

A touch sensor is an electronic sensor used in detecting and recording physical touch. Also known as tactile sensors, it’s a small, simple, low-cost sensor made to replace old mechanical switches we seen in the past.

Based on their functions, there are two types of touch sensors - capacitive sensors and resistive sensors.

Touch sensors work much like a switch. When touch, pressure or force is applied, they are activated and act as a closed switch. When the pressure or contact is removed, they act as an open switch.

Touch sensors, unlike mechanical devices, do not contain moving parts. Hence, they are more durable than mechanical input devices. Touch sensors are robust as there are no openings for humidity and dust to enter.

Working Principle

Touch sensors are also called as tactile sensors and are sensitive to touch, force or pressure. They are one of the simplest and useful sensors. The working of a touch sensor is similar to that of a simple switch.

When there is contact with the surface of the touch sensor, the circuit is closed inside the sensor and there is a flow of current. When the contact is released, the circuit is opened and no current flows.

The pictorial representation of working of a touch sensor is shown below.

Capacitive Touch Sensor

Capacitive sensors work by measuring capacitance and are found in portable devices. They are durable, robust and attractive at low cost.

A capacitive touch sensor contains two parallel conductors with an insulator between them. These conductor plates act as a capacitor with a capacitance value $C_0$.

When these conductive plates come into contact with our finger, our finger acts as a conductive object. This causes an uncertain increase in capacitance.

A capacitance measuring circuit continuously measures the capacitance $C_0$ of the sensor. When this circuit detects a change in capacitance, it generates a signal.

The simplest form of capacitor can be made with two conductors separated by an insulator. Metal plates can be considered as conductors. The formula of capacitance is shown below.

$$ C = \frac{ε_0 * ε_r * A}{d} $$

Where

• $ε_0$ is the permittivity of free space
• $ε_r$ is relative permittivity or dielectric constant
• $A$ is area of the plates and $d$ is the distance between them.

Capacitance is directly proportional to the area and inversely proportional to the distance.

In capacitive touch sensors, the electrode represents one of the plates of the capacitor. The second plate is represented by two objects: one is the environment of the sensor electrode which forms parasitic capacitor $C_0$ and the other is a conductive object like human finger which forms touch capacitor $C_T$.

The sensor electrode is connected to a measurement circuit and the capacitance is measured periodically. The output capacitance will increase if a conductive object touches or approaches the sensor electrode. The measurement circuit will detect the change in the capacitance and converts it into a trigger signal.

The working of a capacitive touch sensor is shown in below figure.

Resistive Touch Sensor

Resistive sensors don't rely on any electrical properties to work. These sensors work by measuring the pressure applied to their surface. The resistive touch sensors calculate the pressure applied on the surface to sense the touch. These sensors contain two conductive films coated with indium tin oxide, which is a good conductor of electricity, separated by a very small distance.

A constant voltage is applied across the surface of the films. When pressure is applied to the top film, it touches the bottom film. This generates a voltage drop which is detected by a controller circuit and signal is generated thereby detecting the touch.

Applications

Capacitor sensors are easily available and are of very low cost. These sensors are highly used in mobile phones, iPods, automobiles, small home appliances, etc. They are also used to measure pressure, distance, etc. A disadvantage of these sensors is that they can give a false alarm.

Resistive touch sensors only work when sufficient pressure is applied. Hence, these sensors are not useful for detecting small touches or pressures. They are used in applications such as musical instruments, keyboards, touch pads, etc. where a large amount of pressure is applied.