Infrared LED / detector design
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From: Jan Panteltje on 23 Feb 2010 06:08 On a sunny day (Tue, 23 Feb 2010 02:04:05 -0800 (PST)) it happened "miso(a)sushi.com" <miso(a)sushi.com> wrote in <6bd4046b-063a-4779-8762-4c733321c6d7(a)a18g2000yqc.googlegroups.com>: >The Texas Instruments website has lots of tips on TIA for photodiodes, >mostly from their Burr Brown acquisition. Even if it takes actual >money (ack!), I suggest using parts with specifications. Digikey or >Mouser will do the job. > >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 microswitch could simplify things.
From: Fred Bartoli on 23 Feb 2010 07:58 Jan Panteltje a �crit : > On a sunny day (Tue, 23 Feb 2010 02:04:05 -0800 (PST)) it happened > "miso(a)sushi.com" <miso(a)sushi.com> wrote in > <6bd4046b-063a-4779-8762-4c733321c6d7(a)a18g2000yqc.googlegroups.com>: > >> The Texas Instruments website has lots of tips on TIA for photodiodes, >> mostly from their Burr Brown acquisition. Even if it takes actual >> money (ack!), I suggest using parts with specifications. Digikey or >> Mouser will do the job. >> >> 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 microswitch > could simplify things. Nah, just leverage the so criticized ROHS and let your Pb free prototype grow whiskers. -- Thanks, Fred.
From: George Herold on 23 Feb 2010 12:19 On Feb 21, 10:30 pm, Matt <hamplif...(a)gmail.com> wrote: > Wow, I had no idea I'd receive this much help here. Looks like I found > the right forum! > > I really don't want to seem like the typical forum dullard and have > y'all hold my hand all the way through this. Anyways: > > I built an emitter driver circuit from an 555 I had in the parts > drawer. It works very well and seems to happily source upwards of > 150mA.... so I'm planning to skip the transistor and just use that to > drive the emitter. > > The detector circuit is being a little annoying however...... or maybe > I'm just being perfectionist again. I'm using a phototransistor, > collector to ground, emitter to +5VDC through a 1k resistor. I pick > the output off the emitter to my scope. > > http://s250.photobucket.com/albums/gg256/spiral_72/?action=view&curre.... > > So the leading edge has a ramp to it, the trailing edge is just what I > expect. Larger values of R-sub-L increase the leading edge angle, > while an R-sub-L or 0ohms will make a nice square wave while pulling > 30mA....... unsuitable for a battery powered application especially > considering this is only a sensor. ARG! > > Anyways, I believe the advice is correct. The emitter and detector are > right beside each other so I don't need to make this any more > complicated than I need to.... I've got the timing circuit right there > for use on the detector circuit.... I'll probably do that, run a HI/ > LOW pass filters and be done with it..... Unfortunately I've been > fighting with the detector square wave thing so I haven't gotten to > that point...... I considered cleaning up the square wave with a one- > shot, but that will trim the leading edge.... I dunno. > > I'll bookmark all the Ir modules you listed. Thank you. I haven't > given up on components just yet. I'm still having fun :) > > Oh, I pointed a TV remote at my circuit and could see the data packet. > COOL! 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.
From: miso on 23 Feb 2010 16:49 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>: > > >The Texas Instruments website has lots of tips on TIA for photodiodes, > >mostly from their Burr Brown acquisition. Even if it takes actual > >money (ack!), I suggest using parts with specifications. Digikey or > >Mouser will do the job. > > >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 microswitch > 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
From: Jan Panteltje on 23 Feb 2010 17:44
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>: >> >> >The Texas Instruments website has lots of tips on TIA for photodiodes, >> >mostly from their Burr Brown acquisition. Even if it takes actual >> >money (ack!), I suggest using parts with specifications. Digikey or >> >Mouser will do the job. >> >> >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. |