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Panel and Case
The front of the case is a single electrical blanking panel. You will need to make a 13mm (1/2" approx) hole in the centre of this for the LDR to protrude through. If you do not have a big enough drill bit or the chuck of your drill will not accommodate one, drill the biggest hole you can and then either file it out or mount the LDR behind it.

The plastic used for these blanking panels is very brittle. It may be worth buying two if you have to travel any distance - just in case! You should get the mounting screws with it. Try to get a panel that is plain on the inside, some have extra moldings and bits which may get in the way. It is not easy to tell when it is mounted on cardboard display packing in a DIY super-store - so try a local electrical shop or trade counter instead.

The panel may be carefully drilled using a hand drill or a SLOW electric drill. A normal DIY power drill will be too fast. A rechargeable cordless drill is ideal since it is relatively slow with good torque - one of these tools is ideal for electronics work.

I found it best to drill a small pilot hole (about 3mm or 1/8") and then go straight to the large size. If you increase the size in stages, the bit is more likely to catch and break the panel. Take it VERY gently when you near the point of breaking through. A WorkMate is useful to hold the panel while drilling.

On the prototype the PCB is held with screws and spacers, however this arrangement is not recommended for safety reasons unless you use the nylon spacers with a threaded insert at each end. A much better solution would be to use two self-adhesive PCB stand-offs. If the board feels unsteady, use two more self-adhesive stand-offs with the top bits cut off, to support the top and bottom of the PCB.

The rear of the case is a 25mm (socket depth) single electrical surface box. Before buying this, make sure it has only two threaded holes for the front panel screws. Some boxes have four of these, one on each edge - the top and bottom ones will foul on the PCB. You will need to remove one or two knock-outs on the side or back for the cables to enter.

Testing
Since there is nothing to adjust, testing simply involves seeing if the unit works. Remember that the whole PCB is at mains voltage and is therefore potentially lethal.

Fit the PCB into the case before switching on. Connect one end of length of two core mains flex to the SK1 terminals (Live nearest to edge of PCB) and connect the other end to a 13A plug fitted with a 3A fuse. Connect another length (at least 1 metre) of two core cable between the SK2 terminals (Live to edge of PCB again) and a lampholder. Fit a 60W lamp in the holder. Position the lamp holder about a metre away from the LDR.

Connect the unit to the mains, preferably via an earth leakage or residual current circuit breaker (the type intended for power tools), and switch on. Hopefully nothing dramatic happened!

Place your hand over the LDR. After a couple of seconds the lamp should come on. Move your hand away and it should go off again. That's all there is to it. Hopefully your unit worked fine - there isn't much to go wrong!

Installation
Installation will vary depending upon what you are using the unit for. My unit is mounted on a piece of wood next to a single 13A socket. Three core mains cable was used, the Live and Neutral pass through this unit, and the Earth connects directly to the socket. The other end of the cable terminates in a 13A plug with a 3A fuse.

It is important to use three core cable if you are using this unit to control a 13A socket, even if you only intend to a load that does not need an earth. At some future point someone may plug an earthed load into the unit.

The prototype was sited indoors on a window sill, with the lead to the outside Christmas lights passing through a hole in the window frame.

The unit can be more permanently installed if required. However it is not suitable for permanent connection to household wiring. This is due to wiring regulations, not a fault with this unit. The unit must always be connected to the mains via a 13A plug and socket, or some other method than can be properly isolated such as a double pole switch.

Do not assume that a load is safe if it is switched off by this unit. This unit switches the neutral line, to reduce the potential difference between the circuit and earth. Also there is sufficient leakage through an untriggered triac to give a fatal electric shock. When working on this unit or a load connected to it, the power must be properly isolated (live and neutral disconnected).

Take care to position this unit so that light from the lamp it is controlling does not fall directly on the LDR. You may be able to mount the unit on a different side of the building for example. Street lamps have the light sensor mounted on the top, above the lamp which shines downwards. You may be able to arrange something along these lines.

If you are mounting the unit outdoors you will need to arrange a suitably waterproof case. The suggested case is suitable for indoor use only. It is imperative that the circuit cannot get wet. The area where the light gets to the LDR may be difficult so seal effectively. A sealed plastic case (to IP65) with a clear lid would be a tidy solution. Use sealed cable glands for the cable entries. Drill a small (2mm) breather hole at the lowest point in the case, to prevent condensation and let out any moisture which might get in despite your efforts.