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Motherboard Circuit Description
The motherboard contains the IR receiver and decoder, together with the power supply. The circuit is shown in figure 2.

D101 is the IR photo-diode and U101 (TBA2800) is the infra-red amplifier. This IC contains three stages of amplification, the first of which has an automatic gain adjustment system to cope with varying signal and ambient light levels. The second amplifying stage simply provides further amplification, and the third separates the wanted signal from the general background noise. An inverting stage is also provided to give both positive and negative outputs.

The overall gain of the IC is quoted as 70dB, and the typical current consumption is 1mA at 5V.

C103 and C104 are the coupling components between the amplifying stages. The values of these have been chosen to give good coupling at the IR transmission frequency, while rejecting lower frequency noise and interference. C102 is the filter component for the automatic gain control of the first amplifier in U101. The power supply to U101 is decoupled by R101, C101 and C105.

The output of U101 will be groups of pulses, similar to those transmitted by the handset. D104, C106 and R102 recombine these, but the rising and falling edges of the resulting waveform are rather imprecise. U104 is configured as a comparator with hysteresis to produce a tidy waveform for U102.

U102 is the HT12D remote control decoder, which was discussed earlier. The valid transmission (VT) output is inverted by Q101, and gated with the data outputs (D0 to D3) by U103. This gating is necessary because the data outputs of U102 remain when the transmission finishes. The appropriate output of U103 goes high when a button is pressed on the remote control handset, and the signal passes to the appropriate lamp control module.

As the total power consumption of the control circuitry including four modules is only about 10mA at 5V, a basic mains-derived power supply arrangement is adequate. The control circuits are connected directly to mains live on the lamp control modules in any event, so there would be no advantage in using an isolated supply from a mains transformer. The mains input is connected to TB101.

In circuits such as this a capacitor (C109) is used to drop the excess voltage as, unlike a resistor, it does not dissipate any power due to the 90 degree phase shift. R103 limits the surge current at switch-on, and R104 discharges C109 when the unit is disconnected from the mains. The +0.6V/-5.6V pulses on D102 are rectified by D103 and smoothed by C110 to give a stable 5V supply, at up to about 15mA. SUP101 is a surge suppressing component.

The test link allows the power supply to be tested (before the control modules are fitted) without being connected to the remaining circuitry. J101 to J120 are the connections to the control module boards, and TB102 to TB105 are the connection points for the lamps being controlled.

Dimmer Module Circuit Description
The circuit, shown in figure 3, is based around the Siemens SLB0586A touch dimmer IC. This IC permits the design of fully electronic dimmers for resistive load incandescent lamps, operated by a single touch sensor or remote control channel. The lamp brightness is set by phase control. The IC contains a phase-locked loop which is synchronised to the mains frequency.

A digitally determined period of approximately 50mS ensures a high degree of immunity to interference in the control inputs, while allowing almost instantaneous operation. The device can distinguish between turning On/Off and dimming by the duration of the control input signal period. A brief pulse (50 to 400mS) will switch the light on or off.

If the input is operated for a longer period the lamp brightness will be varied up and down for as long as the input is operated. The complete cycle takes 7.6 seconds (eg bright-dim-bright) and stops at the chosen brightness when the input is removed. The lamp brightness is varied in a physiological-linear manner to enable easier setting at lower brightness levels.

There are three modes of operation, which are link selectable. In modes A and C the lamp always comes on at full brightness, over a 380mS soft-start period. In mode B the lamp comes on at the same brightness as when it was turned off. In mode A, a dimming operation will start in the same direction as the previous dimming operation, while in modes B and C the dimming will start in the opposite direction. For mode A, join LK203 to LK202 on the PCB. For mode C join LK203 to LK201, and for mode B leave LK203 unconnected.

The supply to U201 is decoupled by R208 and C204. R201 and C201 are the integration components for the internal phase locked loop. L201 and C203 are EMI suppression components. J206 is the signal from the remote control decoder circuit on the motherboard and J203 is the connection point for an optional local touch sensor. R204 and R205 limit the touch sensor current to about 25uA, which is so low that it cannot be felt. For safety the two separate resistors must not be replaced by a single component. Mains Neutral is not required by this module, but the terminal (J205) is provided for compatibility with the Switch module.

The recommended triac is a BT137-600 or a T410-600. The author does not recommend the use of the C206, C216 or C226 range of devices as he has found these to be unreliable in several different applications.