Darth Bagel
New Member
So to set up some background, I just moved into a new house a week ago (yay!), and it has a 1-car garage. Naturally, my wife instantly laid claim to it, and while her car *does* fit in the garage there's only a very few (I'd guess 3-4 total) inches to spare. Naturally, rather than a low-tech tennis-ball-and-string approach I thought I'd take the opportunity to create some needless technological terror to guide the parking process.
My initial thoughts centered on range-finders, primarily ultrasonic ones. However, I'm not sure they've got the accuracy I'd need for this project, especially at the desired ranges. An IR reflection object-detector sort of thing also occurred to me, but I don't want to take the chance of ambient light causing trouble with the calibration, and I also want to be able to accomodate a vehicle in various states of cleanliness.
But I don't really need range. The information I need boils down to a boolean "is the car in the right place yet?" Through some form of lunacy I thought of using a laser mounted either on the ceiling or on a (fairly sturdy) mount well above the car, directed at a phototransistor placed on or near the ground. This keeps the costs minimal ($5 at most?) and the design nice and simple. For now at least.
If you don't care about background, start reading here.
So now the plan, electrically, is to shine a laser onto a phototransistor. When the transistor can see the beam, either no lights or a green light will be on. When the transistor can't see the beam, a red light turns on. By using LEDs for the lights hopefully I can keep power usage low enough that I can just leave it on all the time, otherwise I'll have to put some thought into an easy way to turn it on and off.
So first the laser. I was thinking of even trying to save the cost of a red laser pointer by salvaging the laser diode out of an old CD drive. I like this for two reasons. First, it means I don't have to buy anything. Second, based on what I've seen the standard CD-ROM laser emits a wavelength around 780nm, while all the red laser pointers I see are 700nm or less. 780 gets me much closer to the peak responsivity of an IR phototransistor, and may even allow me to use a transistor with the black-ish ambient light reject lens material. However, I'm worried about its ability to produce reasonably focused light at such a distance since a CD drive obviously doesn't need very long range optics. More importantly, I read on one website that 780nm may be quite bad for the eyes, even just the reflected light. Can anybody possibly comment on either of these concerns?
The transistor is a fairly straightforward issue, and I really only want to ask if anybody has a particular device they'd like to suggest. I was looking at some Sharps on Digikey but they all said obsolete or limited quantities, so I'm not sure if they've been supplanted by a new device I've yet to find.
If by some twist of fate you're still reading after all that, bravo and thanks for your help/comments/mockery.
edit: forgot to mention, I'm located in Rochester, NY, USA.
My initial thoughts centered on range-finders, primarily ultrasonic ones. However, I'm not sure they've got the accuracy I'd need for this project, especially at the desired ranges. An IR reflection object-detector sort of thing also occurred to me, but I don't want to take the chance of ambient light causing trouble with the calibration, and I also want to be able to accomodate a vehicle in various states of cleanliness.
But I don't really need range. The information I need boils down to a boolean "is the car in the right place yet?" Through some form of lunacy I thought of using a laser mounted either on the ceiling or on a (fairly sturdy) mount well above the car, directed at a phototransistor placed on or near the ground. This keeps the costs minimal ($5 at most?) and the design nice and simple. For now at least.
If you don't care about background, start reading here.
So now the plan, electrically, is to shine a laser onto a phototransistor. When the transistor can see the beam, either no lights or a green light will be on. When the transistor can't see the beam, a red light turns on. By using LEDs for the lights hopefully I can keep power usage low enough that I can just leave it on all the time, otherwise I'll have to put some thought into an easy way to turn it on and off.
So first the laser. I was thinking of even trying to save the cost of a red laser pointer by salvaging the laser diode out of an old CD drive. I like this for two reasons. First, it means I don't have to buy anything. Second, based on what I've seen the standard CD-ROM laser emits a wavelength around 780nm, while all the red laser pointers I see are 700nm or less. 780 gets me much closer to the peak responsivity of an IR phototransistor, and may even allow me to use a transistor with the black-ish ambient light reject lens material. However, I'm worried about its ability to produce reasonably focused light at such a distance since a CD drive obviously doesn't need very long range optics. More importantly, I read on one website that 780nm may be quite bad for the eyes, even just the reflected light. Can anybody possibly comment on either of these concerns?
The transistor is a fairly straightforward issue, and I really only want to ask if anybody has a particular device they'd like to suggest. I was looking at some Sharps on Digikey but they all said obsolete or limited quantities, so I'm not sure if they've been supplanted by a new device I've yet to find.
If by some twist of fate you're still reading after all that, bravo and thanks for your help/comments/mockery.
edit: forgot to mention, I'm located in Rochester, NY, USA.