Infrared LED / detector design
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From: Frnak McKenney on 24 Feb 2010 11:48 On Tue, 23 Feb 2010 22:44:59 GMT, Jan Panteltje <pNaonStpealmtje(a)yahoo.com> wrote: > On a sunny day (Tue, 23 Feb 2010 13:49:48 -0800 (PST)) it happened > "miso(a)sushi.com" <miso(a)sushi.com> wrote in ><472e4bc9-f8bc-422a-8186-31bebc090a94(a)b18g2000vba.googlegroups.com>: > >>On Feb 23, 3:08�am, Jan Panteltje <pNaonStpealm...(a)yahoo.com> wrote: >>> On a sunny day (Tue, 23 Feb 2010 02:04:05 -0800 (PST)) it happened >>> "m...(a)sushi.com" <m...(a)sushi.com> wrote in >>> <6bd4046b-063a-4779-8762-4c733321c...(a)a18g2000yqc.googlegroups.com>: [...] >>> >Usually for a project that you release into the wild, you never depend >>> >on one safety mechanism. For instance, if the thing is going to run >>> >into a wall, you would have your photo sensor scheme and maybe a >>> >simple bump detector, even if it is just a plain old switch. >>> >>> Some insects have these feeling 'hairs', something like this: >>> >>> � � / >>> �OOO >>> � � \ >>> >>> Som pieces of spring wire (not pointy, maybe with a rubber tip), and a mi= >>croswitch >>> could simplify things. >> >>I didn't want to get into it, but I would try bumpers made out of >>coax. Stiff enough that they are self supporting, weak enough that >>they will flex. You can get a small voltage generated by flexing coax >>since the cable has a piezoelectric property. This requires a high >>impedance amp. I had a sample of some coax especially designed for >>this "feature", though I don't know if the product made it to market. >>Here it is from a different manufacturer: >>http://www.meas-spec.com/product/t_product.aspx?id=2476 > > Nice stuff! > Of course it depends a bit on the speed of the robot, > I think for low speed you can use this cable, > for high speed you need to start breaking - or steering away earlier, > and maybe use IR or the feelers on micro switches. The simplest collision detectors I have seen are based on spring wire ("piano wire") like that sold at hobby shops for a few dollars. You put a loop on one end and screw that down securely, then place the other end between two screws or a hoop of wire to form the other side of the switch; depending on your needs, you can bend the wire to make it into a NO (normally open) or NC (normally closed) switch. You will need to "debounce" the switch, just as you would with any mechanical switch. Here's one of the odder "antennae" I've seen, where the wire is attached to a microswitch (which also needs debouncing). How to Hack a Rumble Robot (with video) http://www.wikihow.com/Hack-a-Rumble-Robot "Antennae" like this have one problem, though: they tend to get caught in things and/or get bent. If your robot shape allows it, you can bend the wire so that only the "middle" is exposed: ------------------ (very sloppy "bow") / \ Body ====== / ================= \ ==== (=) Mounting (=)\(=) "Contact" screw \ screws You still need to debounce the contact, but there is no free end to get tangled up or tripped over. Then there are "flex" sensors that change resistance based on how much they are bent. And hundreds of other approaches. However, for anyone starting out with robot building I'd strongly recommend choosing a simple bumper switch design and only adding one or two before spending a lot of time thinking about the fancier stuff. It's all too easy to get so sidetracked by dreams of sophisticated hardware that you wind up losing interest in the project because it takes so long to finish. On the other hand, if you start out "simple and stupid", the emotional feedback from seeing one's creation mobile and making noises -- even if it is occasionally bouncing off walls and running into the cat -- helps keep one involved, and provides an incentive to keep improving things bit by bit. Good luck! Frank McKenney -- The tendency to achieve our foreign policy objectives by inducing other governments to sign up to professions of high moral and legal principle appears to have a great and enduring vitality in our diplomatic practice. -- George F. Kennan / American Diplomacy 1900-1950 -- Frank McKenney, McKenney Associates Richmond, Virginia / (804) 320-4887 Munged E-mail: frank uscore mckenney ayut mined spring dawt cahm (y'all)
From: Matt on 25 Feb 2010 09:34 > What's the time base on that 'scope pic? Or, at what frequency are > you chopping the LED? As Tim says a photodiode is faster than a photo- > transistor. You've also got a lot more choice in area size with > photodiodes. The other thing to be aware of is that IR LED's tend > to be slower than their visible cousins. So that delay and turn-on > time you are seeing might be from the LED. You can test this by > blinking a red LED at your circuit and seeing if the respose time > changes. > > George H. The time base is 10ms/DIV, 2V/DIV (both channels). The top waveform is the emitter driven by a 555 at roughly 30kHz. The bottom waveform is the detector circuit output. I'll have to see if I have any photodiodes.... Or if I can get any locally. I've got an order put together for DigiKey.... kinda waiting on money though. ...........sorry for the delay y'all. I didn't realize this conversation had gone to page 2!
From: Matt on 25 Feb 2010 09:44 > >> >Usually for a project that you release into the wild, you never depend > >> >on one safety mechanism. For instance, if the thing is going to run > >> >into a wall, you would have your photo sensor scheme and maybe a > >> >simple bump detector, even if it is just a plain old switch. Good point. I'll do that, especially to keep me from burning up the drive motors. > > >> Some insects have these feeling 'hairs', something like this: > > >> / > >> OOO > >> \ > > >> Som pieces of spring wire (not pointy, maybe with a rubber tip), and a mi= > >croswitch > >> could simplify things. > I actually did this (Revision #1) with two lengths of straightened coat hanger. I works fine. I just wanted something a little more nerd- like :) Plus the Ir is something I've always wanted to play with... This is just an excuse to get started. > >I didn't want to get into it, but I would try bumpers made out of > >coax. Stiff enough that they are self supporting, weak enough that > >they will flex. You can get a small voltage generated by flexing coax > >since the cable has a piezoelectric property. This requires a high > >impedance amp. I had a sample of some coax especially designed for > >this "feature", though I don't know if the product made it to market. > >Here it is from a different manufacturer: > >http://www.meas-spec.com/product/t_product.aspx?id=2476 > Are you serious!?!? Wow, that's incredible..... But now that you mention it, that's how many strain gauges work. > Nice stuff! > Of course it depends a bit on the speed of the robot, > I think for low speed you can use this cable, > for high speed you need to start breaking - or steering away earlier, > and maybe use IR or the feelers on micro switches. Ya, it's no making any skid marks on the floor, but it ain't slack either. At it's speed a collision would shake things up a bit. The limit switches from the original design switched BEFORE it hit the wall. The Basic Stamp reacted in uS since all it was doing was waiting for the switch. It'd be nice to have the 2-3" of Ir range.
From: Matt on 25 Feb 2010 09:47 Thank you Frank.... very cool. I'll see about posting a video of the bot.... It's nothing fancy..... I don't have a Youtube account, but that's easy enough to remedy I guess.
From: George Herold on 25 Feb 2010 11:25
On Feb 25, 9:34 am, Matt <hamplif...(a)gmail.com> wrote: > > What's the time base on that 'scope pic? Or, at what frequency are > > you chopping the LED? As Tim says a photodiode is faster than a photo- > > transistor. You've also got a lot more choice in area size with > > photodiodes. The other thing to be aware of is that IR LED's tend > > to be slower than their visible cousins. So that delay and turn-on > > time you are seeing might be from the LED. You can test this by > > blinking a red LED at your circuit and seeing if the respose time > > changes. > > > George H. > > The time base is 10ms/DIV, 2V/DIV (both channels). The top waveform is > the emitter driven by a 555 at roughly 30kHz. The bottom waveform is > the detector circuit output. > > I'll have to see if I have any photodiodes.... Or if I can get any > locally. I've got an order put together for DigiKey.... kinda waiting > on money though. > > ..........sorry for the delay y'all. I didn't realize this > conversation had gone to page 2! If money is an issue Phil H. says you can use solar cells as photodiodes. I've never tried this and I don't know about the speed issue. You could just run things at a lower frequency. Photodiodes use to be cheaper, the price seems to have doubled in the last few years. George H. |