Don't forget guys that most PID controllers can be set up to run as simple on/off controllers (usually by setting the proportional (P) value to 0-but it will say it in the instruction manual). I agree for our applications we don't need the functions of a PID.
However, PIDs are a nice bit of gear because they give you a current realtime tempeature display of your process temp (ie. vessel temp) that is clear and easy to see, with the press of a button you can look at your set temp and change that up/down as necessary in a second. Throw in a few other features like hi/low indicators and variable hysteresis and you have a pretty good controller that's very easy to use.
For easy of use and fast build time I'd seriously look at just buying two PID contollers (one for mash and one for HLT). There are a few brand new PID controllers on US ebay for about $32US Buy it Now that you can choose between relay or solid state outputs. if you just want to control the pump you could run it straight off the PIDs relay, if you want to control elements you'll need a SSR or build a second relay to handle the extra current draw. I've got quotes off these guys before, I forget what it works out to be but expect to pay about $60-$70 total delivered to your door. Not bad. If you want to search and bid on a few different ones they can be had much cheaper.
http://cgi.ebay.com.au/Brand-New-Digital-P...1QQcmdZViewItem
Perhaps not as beautiful as a full LCD but these will certainly do the job.
I'd also consider recirculating for the full amount of time during the mash rather than turning the pump on and off (personal opinion only). Mainly because I would expect if you turn the pump on and off you would get your mash temp yoyoing because of the lag time. If it's recirculating all the time I'd expect you would get a more even and accurate temp reading.
Reading your temp in the mash, where would you put your probe? If you put it in the middle of the mash tun-that area doesn't cool down as quick as the outsides. If you put the probe on the outer part you don't get an accurate reading of the inner temp. Hopefully with a constantly moving wort flow these temps might be a little closer. I'm not an advocate for placing the controller probe in the mash tun, I like the idea of placing it as per the HERMITs brewery, but I have no experience with either.
Also, if your only going to control the wort flow through the heat exchanger by turning the pump on and off then you don't really need solenoid valves for any bypass loop. If you want to incorporate solenoid valves for fluid flow I would suggest just manually switching them on and off as needed rather than trying to write a program to do it all automatically. Solenoid valves are expensive and will add a hell of a lot of complexity to the system, but good luck if you decide to go this route.
Cheers, Justin
PS. When are you going to get your website up and running with the updates again?
h34r: That said one of them would be mighty nice on the HLT. My capiliary thermostat always goes a bit wonky above 55c in terms of accuracy. Just insulated my HLT may make a difference.
