Frequently Asked Questions

Please contact the factory for pricing on the SmarrtSwitch.   NKK contact information is:

 

NKK Switches

7850 East Gelding Drive

Scottsdale, AZ 85260

Tel:  480-991-0942

Fax:  480-998-1435

info@smartswitch.com

 

Please request the part number(s) and quantity you would like to be quoted on.

Yes, the display has to be refreshed. The drawback to having a refresh circuit in the switch cap is that the controller cannot detect when the refreshing circuit freezes due to the ESD charge.

If the VLC is present, one row of display gets charged for a long time. This may damage the display. If the microcontroller goes to sleep mode, it must disable the VLC.

The timing between the latch pulse of the row that appears darker is longer than the timing between the rest of the latch pulses.

Yes, the LCD in the switch is transflective so the display can be seen with sufficient ambient lighting.

Since the LCD is transflective, it is sunlight readable. However, the reflection from the lens may make it unsuitable for certain applications.

For a large number of switches memory is needed to keep the pictures. For a small number of switches the pictures can be made on the fly using ASCII code and lookup table without using external memory.

The number of modules that a microcontroller can control depends on

• instruction execution time of the microcontroller,
• other tasks that the microcontroller has to perform,
• hardware design, and
• software program.

Example of calculation for how many switches can be driven by a microcontroller:

1. Given: microcontroller with
   • average instruction execution time of 2us.
   • 34% of time to perform other tasks.
   • LP-to-LP of 1ms.
2. Calculate how many modules can be controlled by this microcontroller.
3. Formula for time to refresh one line: (1ms) x (.66) = .66ms = 330 instructions

The data has to be addressed, retrieved, and shifted. The time for each of these tasks depends on hardware and software design. The fastest addressing scheme is to have the buffer of the picture data on the RAM as show below

This scheme has the higher byte of the data pointer holding the module line number and the lower byte of the last module (same number for all the lines). Once the data pointer is loaded, a byte of the data is retrieved and shifted, and the lower byte of the data pointer decrements; another byte of the data is retrieved and shifted and so forth until the lower byte of the data pointer equals zero.

Shifting the data with the microcontroller pins for many modules is very time consuming. In this example we assume the data is written via the microcontroller parallel bus to a device such as the 3-shift register method described above or via serial port (8-bit mode). The shift speed of data must be such that the microcontroller does not wait to write the shift data.

This method takes 3 instructions per byte of data (Load the byte, write the byte to the shift register, and decrement the data pointer.). If the interrupt overhead takes 15 instructions, this microcontroller can control 21 modules: