Adding a Temperature Controller to an Original Bradley Smoker

(Updated with schematic 10/31/2007)

I've been trying my hand at some Charcuterie, and have been working my way
through recipes in the book Charcuterie (Ruhlman, Polcyn, and Keller).

When my original smoker, a Cabelas combination BBQ/Smoker, ceased to work due to  defective gas regulator, I did some research to find a replacement.  I like
to use LP gas, mostly because I have a built in gas outlet near our
deck where I do most of the smoking.

However, the Bradley was appealing because of the ability to load up the
unit with meat and wood pucks, and be able to do other things (go to work,
etc.). It's also easy to coach less-dedicated BBQ chefs (my wife) on what to
do...

After using it successfully to make a number of slabs of Bacon, a couple of
hams, and hot and cold-smoked salmon, some things became apparent:

1) the internal box temperature is highly influenced by the external air
temperature
2) the internal box temperature is influenced by the charring of the wood puck.
Different pucks seem to char at different temperatures; I'm not sure if the
humidity of the puck influences this, but I think it's a factor
3) the 'dimmer' temperature control on the bottom of the smoking box is not useful
for setting a particular temperature

What I needed was a way to measure the temperature in the smoke box, and control the emperature with a thermostat or controller.

Looking at what others have used, I found a PID-type controller (with thermocouple)
 on eBay for $35.  It's a TET-612 model, which is apparently identical to a VTC-620 which can also be found readily.

 I happened to have a Solid State Relay (SSR) hanging around from something else
(doesn't everyone?) so didn't need that -- mine originally came from All Electronics
(http://www.allelectronics.com ). I also had a terminal strip to allow easy connection/disconnection of the thermocouple.  I found a DPDT toggle
switch rated for 125v/10A to use to bypass the controller.

Here's a schematic of how I tied it together...

In this picture, the smoke generator is shown, along with the PID controller, thermocouple, and terminal strip.


(continued)