WebEE

Construction
All the components except the transformers are mounted on a single sided PCB. The component overlay is shown in figure *. PCB construction is straightforward and should present no problems to constructors with some experience.

Before starting the construction, drill out the ten triac mounting holes and the four corner PCB fixing holes to about 3mm (1/8"). Don't forget to fit the ten wire links. Veropins or similar should be used for all off-board connections.

The leads of the LED's should be left a suitable length to allow the faces of the components to protrude through holes in the panel of the chosen case. The '+' on the overlay indicates the cathode of the LED, which is usually marked by a flat on the side of the component.

VR1 may be mounted directly onto the PCB if a suitable print-down component is obtained. Alternatively it may be connected to the PCB with short lengths of flex. On the overlay, the centre pin is the wiper, the left pin is the anti-clockwise end of the track and the right pin is the clockwise end.

The triacs should be fixed to the PCB with M3 or 6BA nuts and bolts. No heatsinking is required. The heavy mains carrying PCB tracks should be reinforced with solder.

When construction is complete, please carefully check the area around the triacs for short circuits and bad joints. Short circuits here could cause a nasty mess when the mains is applied!

The Case
Once the PCB is finished it should be mounted in a suitable case with the transformers etc. For professional use, a solid metal case should be used if the unit is to survive for any length of time (disco equipment leads a rough life)! Try to find a pot with a metal shaft, and use a metal knob. Even for home use a metal case should be used for safety.

The interwiring is shown in figure *. The mains wiring must be carried out with suitably rated wire - possibly the cores stripped out of some mains flex. 6 Amp cable will be adequate for the mains wiring. The connections from the board to the lamp sockets are shown with numbers to reduce the clutter on the diagram.

For the lamp connectors I have used the 8 pin Bulgin connectors which are commonly used for disco lighting. The advantage of these connectors is that either the plug or socket may be safely live when de-mated. (They are also fairly difficult to break - which us good to know when you accidentally drop a speaker cabinet onto one!)

All disco controllers and light boxes are fitted with sockets (Bulgin type P552). Connection leads all have plugs (Bulgin type P551) on both end, and are wired for four channels using seven core cable. There are normally two sockets on the light boxes (wired in parallel), so a number of light boxes may be connected in a chain, with the controller at one end. This is an extremely flexible method of arranging things, since all the leads are the same, and any controller can be connected to any light box.

The standard wiring for these connectors is pins 7 and 8 for common (neutral) and pin 1 for earth. Pins 7 and 8 are linked in every connector, and a single wire is used in the connection leads. For three channel lighting, pins 5, 4 and 3 are the three live connections. With four channels, pin 2 is also used. Pin 6 is normally unused or carries a permanent live feed for motors etc.

In this case I have used pin 6 for a further channel so that the ten channels may be carried on two connectors. Although this is slightly non-standard, no harm will be caused if the wrong light is connected to the wrong controller. Standard 4 channel leads can be used if they are made up correctly (with pin 6 connected).