Information below can be used to make remotes for Canon EOS SLR cameras. I built a time delay remote that allows me to take time-delay/interval photographs.

Canon wired remote (DIY):
http://www.chantalcurrid.com/remoteControl.htm
http://www.peeters.com/300d.html

Using a Canon TC-80N3 remote on 2.5mm plug cameras (best but expensive):
http://sean.wenzel.net/lists/digi_astro/18/9438.html
http://eosdoc.com/manuals/other/TC-80N3/
http://www.deep-sky.co.uk/dslr/dslr.htm
http://www.licha.de/astro_review_canon_300d.php

Tutorials:
http://www.tpub.com/neets/book2/3d.htm
http://www.uoguelph.ca/~antoon/gadgets/555/555.html

Delay/Timer circuits (mostly 555 IC based):
http://www.benlo.com/kap/shutter.html
http://home.cogeco.ca/~rpaisley4/LM555.html#4
http://www.davidbridgen.com/555.htm
http://robroy.dyndns.info/KAP/rig1.html
http://www.uoguelph.ca/~antoon/gadgets/555/555.html
http://www.ladyada.net/make/sudc4kap/make.html
http://www.mikmo.dk/cblfo.html
http://www.siliconchip.com.au/cms/A_30337/article.html
http://www.rocketreviews.com/reviews/scratch/tiny_timer.html
http://www.zen22142.zen.co.uk/Circuits/Timing/ivt.htm
http://uk.geocities.com/ronj_1217/rts.html
http://circuitos.cl.tripod.com/schem/r34.gif
http://www.aaroncake.net/circuits/relaytim.htm
http://www.electronicsforu.com/efylinux/circuit/feb2003/mar99_wiper.pdf

LED:
http://metku.net/index.html?sect=view&n=1&path=mods/ledcalc/index_eng

Potentiometers:
http://en.wikipedia.org/wiki/Potentiometer
http://sound.westhost.com/pots.htm