Skip to Content

Holtek's new generation Touch Key Flash series MCUs are fully integrated with touch key functions, communication interfaces and display functions thus reducing greatly the need for external components. With the features of high S/N ratio touch switch control, power fluctuation rejection and excellent noise immunity, the stability of these touch keys has been greatly improved, thus offering solutions over traditional mechanical keys with their inherent weakness of rapid wear and tear and manufacturing complexity. These features combine to ensure effective and rapid product development in areas such as household appliances and other touch key controlled products.

Application Description Application Description

Question 1

Question 2

Question 3

Question 4

Question 5

Question 6

Question 7

Question 8

Question 9

Question 10

Question 11

Question 12

Question 13


Question 1

How is an external MCU used with the BS80xB devices?

Answer

There are two methods:
a. Use I/O pins on the MCU to connect to the Kout pins.
b. Connect the MCU to the SCD serial interface pin on the devices.

« back


Question 2

How do I manage the unused keys or Kout pins?

Answer

The unused touch keys should be grounded while the corresponding Kout pins can be left floating.

« back


Question 3

How many methods are there for touch key sensitivity adjustment?

Answer

  • (1)The BS812A-1, BA813A-1, BA814A-1, BA814A-2, BA816A-1 and BA818A-2 devices can use external capacitors(0-20p)to adjust the sensitivity. Note that adding capacitance will reduce the sensitivity. If the sensitivity is to be increased then this can be implemented using application hardware techniques such as the following methods:
    • a. Reduce the cover thickness.
    • b. Use dielectric material panel, for example, using glass instead of acrylic.
    • c. Increase the PCB sensor PAD size and ensure that the areas below or around the sensor pad are not covered   with a ground layer.
  • (2)For the BS8112A-3 and BS8116A-3 devices, changing the key trigger threshold by programming the bit0~bit5 bits in the Kn_TH register via the I²C interface can adjust the sensitivity. The recommended value range is 8~63, where higher threshold values result in lower sensitivities.

« back


Question 4

Is an LDO required for BS81xA applications?

Answer

This depends on the power conditions. As the BS81xA devices have excellent immunity against power supply variations, in many application areas an external LDO is not required.

« back


Question 5

How do I use an MCU to communicate with the BS81XA? Is it necessary to connect pull-up resistors?

Answer

there are four methods for an MCU to communicate with the BS81xA devices:
a. Connect the MCU I/O pins to the BS812A-1, BS813A-1, BS814A-1, BS816A-1 Kout pins. The key status can then be directly read. Pull -up resistors are not required.
b. Connect the MCU I/O pins to the BS814A-2, BS818A-2 clock and data pins. Pull-up resistors are not required.
c. Connect the MCU I/O pins to the BS8112A-3, BS8116A-3 SCL,SDA I²C pins. In this case pull-up resistors are required.

« back


Question 6

How is the KEY/IRQ shared-pin setup in the BS8112A-3 and BS8116A-3 devices to use the KEY or IRQ function?

Answer

  • (1) IRQ function: This function which is the default function can be used directly. It can be used as an interrupt or a wake-up pin with a default low level output when a touch key action has been is detected. Another selectable output is an active low one-shot output. This is selected when bit0, which is the IRQ_OMS bit, in the IRQ_OMS Option is set high using the I²C communication interface.
  • (2) KEY function: To select this function, it is required to clear the K12_TH /K16_TH mode bit, which is bit6. The default key trigger threshold value is 16.

« back


Question 7

Is it necessary for the device to be restarted after changing the BS81xA option configuration (OMS/LSC)?

Answer

Yes, the BS81xA options are only detected when the device is powered on. Therefore any setting changes made after power on will have no effect.

« back


Question 8

Do the BS81xA devices have a One Key Active function?

Answer

The One Key Active function means that when more than one key is touched at the same time, only the first touched key is valid while the others are ignored.
At present, only the BS818A-2 BCD output provides this function while the other BS81xA devices do not have this function. However by using an external MCU, these devices also can implement this function.

« back


Question 9

Can the time taken for the BS81XA devices to enter the standby mode from the original normal mode be changed? If so how can this time be changed to 1s?

Answer

At present, 8 seconds after power-on, if no touch key actions have been detected, the BS81XA devices will automatically enter the standby mode. This time cannot be changed.

« back


Question 10

Are there any restrictions to the shape and size of the sensor pad?

Answer

The Key Pad shape can be round, square, triangle or any other shape which can be solid or hollowed-out. Round or square shapes are recommended. With regard to size, in the case of a round pad for example, it is generally recommended that they have a diameter of 8~15mm, but should not be less than 5mm. The larger the pad size then the higher the sensitivity.

« back


Question 11

How thick can the switch covers be? What is the sense range distance?

Answer

The cover thickness and sensing range depends upon the PCB sensor pad size, the space between the PCB sensor pad and GND, the gap between the PCB sensor pad and the cover as well as the cover material. The PCB sensor pad must be affixed in close contact with the cover. Any gaps here together with the cover material type will affect the sense range distance When using acrylic material, the acrylic thickness can be up to 5 mm, although 2~3 mm is suggested. For glass, the thickness can be up to 10 mm, although 4~6 mm is suggested.

« back


Question 12

What special points should be noted for the sensor pad routing to ensure best interference immunity?

Answer

For the pad routings, it is recommended to use direct routings without vias. If it is not possible, the number of vias should be kept as low as possible. The routing should not be longer than 30cm and not shorter than 3cm. The pad routings should be kept as far away as possible from high frequency interference sources, such as RF, Bluetooth signal sources.

« back


Question 13

How is the key wake-up function used in the BS8112A-3 and BS8116A-3 devices?

Answer

How is the key wake-up function used in the BS8112A-3 and BS8116A-3 devices? Answer: The BS8112A-3 and BS8116A-3 devices provide specific key wake-up functions or all keys can have a wake-up function. This is enabled by setting the corresponding KnWU bit(bit7)in the Kn_TH register. The default configuration is for all keys to be enabled with a wake-up function.

« back