Time Lapse Intervalometer for SLRs with 555 timer IC

Step 1 Planning, Schematic, Materials

Below is a schematic that I made with free schematic software from ExpressPCB. You can also download the .sch file if you want to edit it. Remember, that won't get you a PCB to burn, only a schematic to mess around with.
Here's what this circuit will do. When you turn it on, the camera will get a false signal and take a picture. Then the big capacitor will slowly fill with charge while the green LED is on. How slowly is chosen by the variable resistor. When the cap discharges, the 555 outputs a signal to the transistor which connects the shutter control to ground. The red LED lights up and the camera takes a picture
Repeat.

There are also buttons to use the box as a remote shutter release when the circuit is off.

As you can see you need some stuff. Here's a list:

Materials
Resistors: 100k, 470k, 33k, and one 1M variable
Capacitors: 220µF, 0.1µF
LED's: Green, Red
Transistors: NPN-type switching
555 IC timer chip
IC holder socket (to switch out a bad chip)
Protoboard and then later a Radioshack IC PC Board
9V battery
On/Off switch
Momentary buttons,
Battery clip
For Pentax DSLRs, Canon Rebel's, and maybe some others:
Cell phone headset with 3/32" 3 conductor plug (make sure it works, but go cheap)
Extra wires
Project box
Soldering and wire stripping tools and such

Cost:
555IC: $1.69
IC PC Board: $2.49
Handsfree headset kit: ~$5
Other bits and bobs: ~$10
So it all can be had for under $20 and some effort.