Right it's been ages since my last update because I've been busy with my other projects (which I might write about here at some point).
It's gone beyond the point of annoyance now having to use non-rechargeable 9v batteries for John's logic supply. Thankfully I had a suitable target to provide a solution to this problem, in the form of a RC monster truck which was a birthday gift from last year. It uses a 6v re-chargeable battery pack and has a funky recharger. Here it is in all its glory before it meet the inevitable doom:
And a pic of the underside, where you can (sort of) see the location for the battery pack, and the battery itself in the charger:
Armed with screwdriver, hacksaw and drill, I swiftly turned it into a collection of wheels, cogs, and bits of plastic. Unfortunately the battery holder thing was still far too big for John so I had to chop it right down to just the contacts and the top bit of plastic, otherwise it was never going to fit anywhere. The finished product looks like this (apologies for the crap blurry pics as ever, I will address this from my next post onwards!)
Wonderful. It's still a bit big for my liking but it will do for now until I come across a better sized one. In my previous post I mentioned John's shortcomings, especially not being able to see directly in front of him at floor level, so I thought I would re-use more of the monster truck to create an infrared sensor array to address this shortcoming. If you look in the picture of the truck you will see silver decoration type bits on the sides, the top slit of this is the perfect height for the infrared LEDs and receivers. I need two sets of these, pointing away from each other, one at each end. This allows mostly the whole area in between the fronts of the tracks to be covered by the sensors. I need to be careful here though as if the sensors can see the tracks this will fail miserably, thankfully I'm not going to secure them in position, so tweakage is possible once installed.
The infrared emitter is pretty much the same that is used in all remote controls for the tv and such like, it's just an LED which emits light within the infrared wavelength at 980nm. The emitted light bounces from objects and enters back through the detector, thus allowing detection. The detectors have an optical filter which lets through very little light except that with a wavelength of 980nm (using a photodiode). It also has an electronic filter that only allows light being flashed at around 38.5khz to pass through, so those two things combined make them quite isolated from ambient light. The emitter itself has a shielding around it that makes the light shine more like a car's headlights, rather than a big flood of light. This is obviously better for accuracy.
here's some rubbish pics of the finished product.
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I seem to have lost all my schematic files, so I'm going to have to remake them from scratch :(