The Simmer Stat. Click on the thumbnail for a higher resolution photo.

I cut out three cards:

1. The electronics card, on the left of this photo, made from Matrix board
2. The capacitor card, in the centre, made from Stripboard
3. The power control card on the right made from Matrix board

The ABS box has 6 sets of small grooves along the long side and 4 along the short side which you can see in the high resolution photo. I cut the cards 47mm tall and 95mm, the full width, at the top tapering down to 92mm at the bottom. This allows them to slide into the grooves which are closer together at the bottom than the top. The box is actually 54mm deep so there is plenty of room for wires to pass over or under the cards.

This photo has the best picture of the power control card because the mains cables are too stiff to allow me to slide it out. The card contains the relay, the relay coil diode and a piece of connector block for the mains connections. Because all of the wires going to this block are quite heavy I drilled a hole through the card at each end of the block and passed a tie wrap around to fix it securely. The relay has 6 pins: Two for connection to the coil at one end and four at the other end for connection to the contacts. As this device is going to handle up to 13A (there's a 13A fuse in the mains plug of course) I used two bits of 2.5mm² mains wire between the connector block and the relay contacts; soldering them to the two sets of contact pins. This shows the internal connections of the relay; so you need to connect the external wires one to A and B the other to C and D so that both pins in each set carry half of the current.

I fitted the relay with the coil at the top so that the nasty voltages are as far away from your fingers as possible if you are operating it with the bottom of the box off which you might do in the unlikely event that it needs debugging.

Here's the top of the electronics card which was made from Matrix board. I simply fitted the parts in a fairly logical position and used the single core wire to connect them up. The connector block for the 24V supply has only fairly light wires going to it so I fixed this on with super glue.

Here's the bottom of the capacitor card. I arranged the capacitors in three rows. As each period, in general, needs more than one capacitor I used one copper strip in each row as the common, negative, rail and the adjacent strip for the positive side of each capacitor set; cutting the strip between each set. I allowed an extra hole on each set to connect the wire which goes to the switch. I connected all of the common, negative, strips together and wired this to the negative side of the electronics cards negative power rail.