hi I am working on a project that I want to heat up something lets say a nail with an arduino I only want to make the nail about 4-8 degrees hotter how would I do that? also If I wanted to scale up the project lets say a grid of 6x6 how would I do that? I have been trying but seem to always sock myself or start small fires can anyone help?

Basicly I want to turn a bed of 6x6 nails into a dot grid and make them produce heat insted of light is this possible?

It depends on how tightly you need that temperature controlled, and whether it's 4-8 degrees above ambient temp (regardless of what ambient is) or if it's a specific temperature you're seeking.

Specific temp will require a feedback loop with a temperature probe on at least one of the nails, and then as long as you're consistent with the material weights, holding substrate material (ie. board that they're nailed into) you should be able to apply the same effect to the other nails and have the results be within a 4 degree range.

My thought for the actual heating would be a pulsed voltage output from the arduino such that the internal resistance of the nail causes the heat and the pulse duration and frequency are determined either manually (trial and error until correct) or by the aforementioned feedback loop.

I'm sure others will have some ideas here as well.  What's the intent of the project?