juraschek@gmuvax.gmu.edu (05/14/91)
Wanna build a device to allow me to scan an object to detect heat levels at different points. For example, I aim it at a stationary, running car and get a scanned image of the car in terms of the heat eminating from it. (I want to do thermal imaging, in other words.) Would like to interface to a PC. Any ideas where to start and what kind of sensors to use? (Don't wanna spend a lot of $$$. Also, I recognize that I have to use plastic instead of glass for lenses because of the IR glass absorbs. That's the kind of hints I am looking for, as well as a pointer to some sample circuitry.) Thanks. -Dave (I have no farking .sig)
whit@milton.u.washington.edu (John Whitmore) (05/14/91)
In article <1991May13.130630.51341@gmuvax.gmu.edu> juraschek@gmuvax.gmu.edu writes: >Wanna build a device to allow me to scan an object to detect heat levels >at different points. For example, I aim it at a stationary, running car >and get a scanned image of the car in terms of the heat eminating from it. >(I want to do thermal imaging, in other words.) If you can get a mirror, there's a VERY old device that will work for this. It's called a galvanometer. You get a thin quartz fiber for a torsion spring (pull your own! It's fun!), a single-turn loop with dissimilar metals (the winding of the galvanometer is actually a thermocouple), and position the bottom couple of the loop in the focus of the mirror. Apply a magnetic field to the loop, and you're set. To get fancy, operate a second current loop, from a D/A on the PC, to null the galvanometer (i.e. balance the heat-generated current with a known current). It would also work to position a light bulb to shine on the second couple, and brighten/dim this lamp from the PC. Imaging, however, will require motors and mirrors. In any case, a small mirror cemented to the loop can bounce a light beam to make a massless 'pointer'. A couple of photocells straddling the beam can generate a difference signal whenever the pointer budges from center, and the PC can detect this and close the feedback loop through the D/A. There's an example in the British Museum science/technology section, that purportedly could detect the heat of a candle at circa one mile. The date on the exhibit was over a century ago, and it did NOT employ a PC, as I recall. John Whitmore