Arduino stoplight web server

Step 5 Create the relay control circuit (low voltage half)

Because of time constraints, I created this on protoboard using a variety of different techniques.  This worked well enough, but it would have been much easier if I had had time to have the circuit printed. If for no other reason, printed boards are more fun to solder.

Even though I did not have the circuit printed, I did lay it out in eagleCAD so I would know if the parts would fit in the protoboard and enclosure I was preparing to order.  The attached zip file includes the schematic and the board layout.  Please note, the board layout has never been tested.  I believe it will work because I followed the layout when prototyping, but you can never be sure until you set the printed result. Instructables user nickbart successfully printed the board and documented the results on his blog, so you can safely have it printed.

If you choose to have the board printed, this step is fairly simple.  Insert all the components through the top as shown in the layout and solder each of them.  You then are ready to move onto the next steps.

If you choose to do it by hand on protoboard, here are the steps I took to freeform the layout.
Do all of these with the circuit diagram handy to check your work.

1. Print out the board layout, showing both the top and bottom copper layers, as well as the labels.
2. Cut along the outside lines until you have a layout the same size as the board.
3. Tape the paper layout to the protoboard on the side without copper.
4. Lay out the relays and other components using the circuit diagram to show you what needs to connect to what.  You should lay out the relays, the 6 pin header and the power block as shown on the layout, but when it comes time to add the transistors, resistors and diodes in some cases it makes sense to place them in other places, to be near where they connect.  That's because laying out for a printed board has different placement constraints.  On a printed board component don't usually need to be near another one, but there are only two planes (top and bottom) to run the traces.  But when running your own wire, you can cross as many wires as you like.  At the same time, each time you can place component right by the pads it needs to connect to, you can skip running a wire entirely.
5. Where possible, place component leads next to each other.  This will allow you to make solder bridges across the copper pads and save running a wire.  For example, the collector of each transistor and one end of each diode connect to one of the relay pins, so where there is room, you can place them all adjacent to each other and solder them together, possibly twisting the leads together and cutting them off later.  DO NOT CUT ANY LEADS until you have accounted for everything that needs to connect to them.  In particular, you will need to leave leads out if you are planning to use wire wrapping techniques.
6. For the 5 volt parts I used wire wrapping to connect to the leads of the resistors and transistors.  If you don't have wire wrap wire and a way to attach them, you can use the same 22 gauge wire that you will use for the other parts of the circuit.  Using wire wrap allows you to run a very fine wire directly across the bottom of the circuit.  Strictly speaking, wire wrapping should be done with special square posts instead of the round leads that the resistors have, so after they are attached, they should be finalized with a small blob of solder to keep them on.
7. Where a thicker wire needs to be run (for paranoia's sake I used 22 gauge wire for the 9 volt parts) run them across the top and treat them like other component.  That is, poke them through holes in the protoboard near where you want to connect, bend the wire over to connect to the component, and then solder.

Leave the 120 Volt connections unconnected until after the next two steps.