Step 1: Building the 5 Volt relay circuit
Here is a series of mini steps to help build the 5 volt relay circuit. Keep in mind the higher the values of capacitors you use the better off you'll be in the long run.
Step 1. Plug the 555 timer into board.
Step 2. Apply power and ground wires to timer chip.
Step 3. Plug 5v relay (I'm using the reed switch style) into the board, applying 555 timer output to relay power and ground to ground.
Step 4. Connect pin 2 and pin 6 of the 555 timer with a jumper wire.
Step 5. Connect 470K resistor from power to pin 2.
Step 6. Connect 470K resistors from power to pin 4.
Step 7. Connect photoresistor from pin 4 to pin 6.
Step 8. Connect pin 6 to ground with jumper wire.
Step 9. Connect a non-Zener diode so that the cathode connects to the power side of the relay and the anode connects to the ground side of the relay. (This is used to keep sparking from happening when the relay turns on and off)
Step 10. Connect 470 ohm resistor from power to an open end of the switching contact. This step differs depending both on relay rating AND what you plan on switching with the relay.
Step 11. Connect LED to other open contact and ground it. This step differs depending both on relay rating AND what you plan on switching with the relay.
Step 12. Plug 12v regulator into board.
Step 13. Connect the ground of the regulator to ground and the output pin to power on the board. (Your wall source power is connected to the power INPUT on the REGULATOR.)
Step 14. Connect a capacitor from output to ground on the regulator.(Remember: Your capacitors must be rated to handle your source voltage.)(Remember: Your capacitors must be rated to handle your source voltage.)
Step 15. Connect one or more capacitors to the power side of the relay, remember the higher the rating (to an extent) the better! (I'll explain why in the last instructable step)
Step 16. If you plan on using a wall supply, DO NOT JUST GO BY WHAT THE WALL WART IS RATED!!! (As evidenced by two of the photos above) Even I didn't believe that the wall wart was immune to differences in its rating, so use a multimeter to check for the ACTUAL voltage and amperage.