Parts List for Electronic CO2 Controller

None of these parts are especially critical -- just about anything should work.  All parts are available at Radio Shack
C101         100u electrolytic *
C102         0.01u
C103         0.1u **
C201         1uF electrolytic *
C202         0.01uF
C203         0.1uF **
C205         0.1u
* Leakage in the timing electrolytic capacitors significantly affects their performance.
(Actual time intervals may be considerably lower than calculated.)

D201         1N914 or similar (not at all critical)
D202         1N914 or similar (not at all critical)
D203         LED                     (not at all critical)
R101         10k
R102         1k
R103         1Meg variable *
R201         10k
R202         1Meg variable *
R203         100k
R204         1k
R205         100 (The LED in the Solid State Relay seems to need a lot of current.)
* Keep leads short in this high impedance part of the circuit.
Pulser        555 Timer IC (or 1/2 556)
Timer        555 Timer IC (or 1/2 556)
Solid State
Relay         Sharp S101S05V (Radio Shack stocks this,  part number 275-310)
Small 5 volt DC supply (e.g the Radio Shack 273-1454 6 Volt 150mA "wall wart" style -- about $8.00).  It doesn't need to put out much current, but should be well regulated.  Just about anything should do.