PID to control mash temp Options

[swampstander]

I have a HERMS system with my coil in my HLT. I currently monitor the temp of the mash and switch the pump on/ off to recirculate the wort as needed to maintain mash temp. My mash tun is an insulated keg and I typically only have to turn it on once maybe twice at the most during a one hour rest. My temps usually return to where they need to be in a few minutes. Occasionally I overshoot because I typically have buddies over on brewday and they break my concentration. I am interested in using a PID to monitor the temp of the mash and turn the pump on and off as needed. It seems like most of the setups I see here and on other sites recirculate continuously and use the PID to turn on/off the element/ burner for the bath the coil is in or the element for a RIMS.

Is my idea feasible? Can someone recommend the parts I need. I was going to attempt it with a johnson controls temperature controller that I have but it seems to have stopped working. I assume I will need a relay of some sort.

[pilsenhammer]

I used to use a HERMS, manually, and I would open a bypass valve to divert the wort past the coil, rather than raising or lowering the temp of the water in the HLT. That way you can simply stop heating the wort (IE, stop it from going through the coil) while still recirculating until a temp rise is needed again. This can be done using a PID control set-up to operate the bypass valve and also to maintain the temp of the HLT. Or if you prefer, use it to turn the pump on and off.