The heated lid

Now that the heat sink is ordered, on to the heated lid. The lid is a major component of the OpenPCR machine. It eliminates the mineral oil that screws up experiments of newbies and professionals alike. More importantly, it’s the one part of OpenPCR that you’ll interact with *every* time you do PCR. It needs to be done right.

As I’ve shared with a lot of you, our prototype lid is nichrome wire and silicone tape, sandwiched between two plates of aluminum in a wooden lid and it needs a lot of help. A few posts ago, Josh figured out that a peltier device + aluminum plate would fit the bill, and a custom board heater was suggested as something to try out long term.

Getting hot is only half of the story. The hot piece of aluminum needs to make good contact with the top of the tubes (which can have minor variations in size) — which means flat AND compressed. One idea that was suggested was a double hinged lid that would be able to rotate to be flat for a range of tube heights – kind of like the lid on a scanner, which can accommodate paper, thin magazines, and thick books. We also need a good downward force on the tubes, so that good contact is made. After wrangling on it for awhile, I’m going to try a lid on a single springd-hinge to handle compression and a piece of thermal pad (stock image below) to make contact with the tubes. Bought some on Mcmaster (spring hinge) and digikey (thermal pads, various softness, 2.5 – 3 mm, capable of 100-150C+). I think this will be straightforward to use, cheap, and reliable. We will see :)

We’ve got the aluminum parts on hand to test out these components, but we’ll need some better plates to test with. I’ll be working on putting together a design doc for Ponoko to get the flat aluminum parts made, as well as the case (wood or plastic).

If you want detailed specs, sign up as a donor to OpenPCR. For only $32 you get behind the scenes months before anyone else with access to photos, design documents, and software for the OpenPCR project.