UM0756

Using the front panel board

Doc ID 16031 Rev 1

19/28

Figure 18.

Standby of system after timeout

When the system is in standby, the front panel is also disabled and the touch keys and

rotary encoder do not work.

Now when the system is in standby and the standby switch is pressed again, the front panel

exits standby mode and switches ON the power of the host system using the on-board relay.

The front panel displays the channel number and volume on the LED display and the power

LED glows green (Figure 5).

4.3.3

Buzzer

The system has an on-board DC buzzer which is used to improve user interaction. The

buzzer is driven from the LED digit output of the STLED316S device. For details of the

circuit, see the schematic in Section 6.

The buzzer is controlled by the STLED316S and a transistor. The digital output of the

STLED316S device switches ON/OFF the transistor to turn the buzzer ON/OFF.

As the STLED316S is a scanning device and brightness of a particular LED digit is

controlled by the duration that the digit is kept ON during one complete scanning, the

intensity of the buzzer volume varies greatly with the brightness setting of the digit. In the

system there is no change in the volume of the buzzer when the brightness is changed

using the touch keys or rotary encoder, but if the brightness is changed using the

potentiometer, then the buzzer volume varies (Section 4.3.4).

4.3.4

Potentiometer

The system has an on-board potentiometer which can be used to set the brightness level of

the LED display. With the rotation of the knob of the potentiometer (clockwise/counter-

clockwise) the value of the resistance connected to the ISET pin of the STLED316S is

changed and therefore the current flowing though the LED digits is also changed, causing

the brightness of the display to vary.

The variation of the brightness using the potentiometer is a hardware setting, and thus it can

be changed at any time without entering brightness mode.

Note:

The maximum and minimum brightness of the LED display is set by the value of the

resistance connected to the ISET pin of the STLED316S device which in turn depends on

the potentiometer.

A minimum value of the ISET resistance is required for the buzzer to work. Thus the

potentiometer should be set accordingly.