As a sort of weird side project, I'd like to make an oven timer that has selectable food stuffs and associated timing information. Now while this device would be simple to make I would like to stick it on the oven which means it would have to deal with some significant but not ridiculous temperatures (gas oven, metal structure). Has anyone has any experience heat proofing things like HD44780 LCDs, AVRs and other delicate components or do I have to go and get hold of those military grade parts?
Typical ovens with electronics use a back panel to place the electronic components on. Putting an additional panel above or to the side of this panel will provide the best location. Mark has a good point though test the temp experienced at the location you plan to put the project before you start to build. Each component you use should have a rating given by the manufacture of the max heat the component should be exposed to. You may also consider using an old pc fan to place in the enclosure to aid in keeping everything cool.
Do you really need to put the electronics in that environment? Couldn't you simply use high temperature wire for the sensors and such, then mount the electronics in a slightly cooler location? Not trying to be mister obvious here just asking to understand. An oven is a rather dangerous appliance to automate, not that it can't be done safely, just that you need to make sure you have proper fail safes and such. I have built some very large kilns that were gas fired so I do understand some of the challenges with dealing with the heat. I always tried to remove any electronics to a temperature friendly zone.
There's always and only three ways for heat to transfer: radiation, conduction and convection. Account for all three by shielding, isolating, and "mitigating".
That said, sticking electronics (of any kind) in an oven is not a great idea; out-gassing could occur with the plastic parts and thermal cycling is a great way to check the reliability of parts and their interconnects.
For temperatures above the 'normal' industrial range (say 70C), it's not just the military grade parts you'll need, but (perhaps) the ceramic PCBs, the heavy traces and bomb-proof assembly. It's why they're so expensive.
Much, much cheaper is what Mark B said, get the electronics outside, and just sense the temperature.