WebEE

For safety the PCB should be mounted on self adhesive standoffs. Do not use metal screws which will be accessible on the outside of the case. Take care to position the PCB so that the LED's will fit through the LED clips in the front panel.

The transformer should be mounted where the leads will reach the appropriate PCB terminals. Nylon screws or some other insulated mounting should be used, otherwise any metal fastenings accessible on the outside of the case must be earthed.

On the prototype, the leads from the Christmas lights were simply bought in through holes (fitted with grommets) in the back panel, knotted to prevent them being pulled out, and connected directly to the terminals on the PCB. Since they only have to be connected and disconnected once each year, I can live with the slight inconvenience! If you prefer, you could mount suitable sockets on the rear of the case, and fit matching plugs to your tree lights.

The mains wires from the transformer and the mains input cable are connected to SK4. The secondary leads from the transformer connect to the X1 terminals, the centre tap wire (normally black) must go to the centre terminal. No earth connection was used on the prototype, since the case is insulated and the lights do not need an earth.

If you choose to add a speed control pot on the front panel of the case, you will need to use an earth connection, and earth the metal case of the pot. The only exception to this would be if the pot had a plastic threaded mounting bush and a nylon shaft.

Testing.
WARNING. POTENTIALLY LETHAL MAINS VOLTAGES ARE ACCESSIBLE WHEN THE COVER OF THE CASE IS REMOVED. DO NOT CONNECT THE UNIT TO THE MAINS UNLESS THE COVER PROPERLY FIXED IN PLACE. ENSURE ANY EXTERNAL WIRING IS CARRIED OUT SAFELY, IF IN DOUBT CONSULT A SUITABLY QUALIFIED PERSON. PLEASE TAKE CARE WITH MAINS ELECTRICITY - WE DON'T WANT TO LOOSE ANY OF YOU!

Do not connect any lights to the unit initially. With the cover in place, connect the unit to the mains, preferably via a RCD or earth leakage circuit breaker. The front panel LED's should flash in the sequence described earlier. If you have added a speed control pot, this should vary the speed as expected.

If all is well so far, disconnect the unit from the mains and connect a set of Christmas lights (or a table lamp with 60W bulb) to each output. Refit the cover and test the unit again. The lights should operate in the same sequence as the LED's.

If this is OK, leave the unit running for about 15 minutes. After this time, disconnect the mains, remove the cover and check that nothing is getting too warm. The transformer may be warm (not hot), but the components on the PCB should be cool.

Assuming all these tests were satisfactory, the unit may be put into use.

In use.
Because of the somewhat delicate nature of Christmas lights, I would strongly recommend the use of a RCD or earth leakage circuit breaker (the type intended for power tools) - particularly if children are about.

To reduce the risk of fire (due to hot lamps coming into contact with decorations or wrapping paper), the lights should be switched off at night and when no-one is around. There's no point in wasting the electricity anyway!

Do not be tempted to compromise on the safety of your wiring, just because it will only be used for a few weeks. If you must use terminal block connectors to extend cables, cover them in a generous quantity of insulation tape.

Do not use indoor lights outside, purchase a proper set of outdoor lights.

The above precautions apply whether or not this flasher unit is being used. Statistics show that the number of accidents in the home increase around Christmas time. Please don't be a statistic.