Hi Adam,
As Casdsys pointed out there are simpler ways of doing this. An 8pin PIC could do the timing, either with just a pot to give a continuously variable timed pulse – repeatable to within 0.5%, or with just a switch to program in any time period. It could probably provide for the touch sensor, also. I assumed you went the 555 route because you were unfamiliar with programming a PIC – but if you prefer to go that way, just say.
I have redesigned the 555 and built and tested it (Fig 4). I have added a spare switch from the 4066 package, and the rising voltage on C1 as it charges is now fed to the 4066 CNTR pin, and that switches pin6 to V+ to reset the 555 at the end of the timed period. That isolates R1/C1 from the bits around pins2 and 6 and allows C1 to charge correctly.
There is a difference in timing now, because originally C1 reached 2/3 V+ before resetting – now it is nearer 1/2V+. So it will be necessary to increase the value of C1.
I went back to my generic toggled 555 where the charge on C2 sets or resets the 555. It works faultlessly using a push button.
Now the touch plate circuit (Fig 2). I assume the devices Casdsys mentioned work on a change of charge, and that can either be –ve or +ve, whereas the plate considered here works on the 50Hz or 60Hz static that the body picks up from the mains supply. Its amplitude will be variable depending on local conditions, hence the variable pot I put in for sensitivity adjustment. I had to increase C2/R4 to integrate the signal, and found it would work OK (with a lot of electrical stuff operating near me) when R1 slider was at the bottom end (minimum sensitivity). Maximum sensitivity is just below the voltage at which the CNRL pin turns on the switch. Beyond that, of course, IC1 OUT will stay high and keep A switched to B.
I don’t know what your end product is and whether you are dead set on using a plate, but I thought of other ways.
1. A pair of LDRs so that the hand could shade one from the light.
2. A movement detector like this.
http://www.ebay.co.uk/itm/Mini-Adjust-I ... 20ce47a9a6
Best regards