Before the components are placed PCB the box and PCB should be drilled for the mounting holes, and any necessary filing performed. If you elect to use the UK socket back-box, then countersink the front panel to take countersink M3 bolts, so that the front panel labelling can be glued over the top and hides the screw heads.

In these instructions I assume you wish to follow my original design, without modification. You are of course free to completely re-arrange the circuit for your own mechanics, in which case ignore what follows. There is nothing critical about the PCB material, and the layout is very tolerent, so even the whole timer made on veroboard, if this is easier.

Using my PCB layout, one recommended order of soldering components onto the PCB is as follows

1) Resistors (note that on the PCB the LED segment limit resistors are 0603 size surface mount components, but if this is not convenient then it is fine to drill 0.8mm holes by the square pads, and fit leaded resistors in the conventional way.)

2) Displays

3) PIC and ULN2003

4) Eveything else.

but of course this order can be changed.

Make sure the flexible leads for power supply and ground, relay drive, and the two push buttons are firmly attached, and wrapped round the IC legs to prevent the pad pulling off the PCB. If the PIC is to be programmed after mounting on the board, add leads to the 5 pins indicated in the circuit as connecting to the programmer. If the chip is to programmed in a socketed programmer, then this is not necessary (if you ever intend to re-program the PIC then either a socket is needed to let the chip be removed, or temporary fly-wires added).

Some components are not on the original PCB at all, these mount on veroboard, and are attached inside the box (while the PCB attaches inside the lid) these are the bridge rectifier, which are is a 1A module, although 4 single diodes could be used as an alternative, electrolytic capacitors and voltage regulator.

In the original design the relay was an enclosed "Finder" part, contacts rated at 250V 16A. Mains rated wires were soldered directly to the relay contact pins, and these encapsulated in ‘araldite’ epoxy made into a solid square with a temporary tape mould. If you have a glue gun, hot melyt glue is just as good, and faster.Totally enclosing the erlay pins is probably ‘over the top’ but once only the low voltage parts are open to touch, the circuit is deliberately made safe for testing and debugging on the bench. The mains wires can be made long enough to reach to a proper junction box where the boiler supply is interrupted, for tests a supply and light bulb can be substituted.

Relay before and after encapsulation of wiring (thick brown/Blue are mains cable cores, red/black are for 12 V)

The seven segment displays SC08-11SWRA from Kingbright/LED technology, the omrom push buttions, and bridge rectifier.

The veroboard carries, from left to right, a capacitor, the bridge rectifier, the 5 V regulator that takes the 12V to 5V. Lurking in the background, behind the regulator is the resistor that picks off the AC used as the timing reference.

The PCB before adding components.

Start adding stuff, and if unlike me you put all the displays in the right way up first time, your soldering should look at least as good as this!

If you don’t trust your soldering then before both of the PIC and ULN2003 are fitted (either one is OK), you can use a meter on ohms to buzz out that all the segements and resistors ar connected OK.