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We all love summer vacation but there comes a time when you get bored of your Xbox and decide to start off a new project to keep you busy.

Well this is what happened to me and I decided to build an Arduino controlled interactive LED table surface after watching a couple of demos on Youtube. The sensor I was going to use for interaction was RPR359F Photosensor since I had already used it earlier in a project. However, at that time, I managed to get as many of these as I wanted from the university as it was a part of a course. But I was astonished when I tried to buy it myself. The damned thing costs a lot.

Since I need nearly a hundred of them so now I am looking for a cost effective alternative to those photosensors to use it in my project. I was wondering if the LDRs are what I am looking for but wouldn't the light feedback effect keep them always on. And I am not even sure if they would be able to detect the user's hand as efficiently as those photosensors could do.

Please suggest any other cheap solution and also comment on the LDR's usage.

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  • \$\begingroup\$ Just how much are you willing to pay? And could you provide a Youtube link so we can see just what you're thinking of? \$\endgroup\$ – WhatRoughBeast Jun 22 '15 at 19:20
  • \$\begingroup\$ 100 of those things cost about 150. Not terribly expensive. You could buy the phototransistor and IR LED as separate base components to save money. Or you could do the smart thing and buy a handful to test your idea out before going in for the whole 100. Then you can worry about sourcing cheaper comps. \$\endgroup\$ – I. Wolfe Jun 22 '15 at 19:23
  • \$\begingroup\$ Video<-link to the video. \$\endgroup\$ – Muhammad Ali Jun 22 '15 at 19:33
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The sensor you mention is just a phototransistor and an IR LED in a housing.

Maybe you could 3D print frames, use drilled holes, or otherwise replace them (spacers or shrink tubing over the parts?).

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  • \$\begingroup\$ Thank You for your response sir but I don't have access to a 3D printer. Furthermore, the IR LED and photosensor would also sum up to be quite expensive since I need nearly a hundred of the sensors. \$\endgroup\$ – Muhammad Ali Jun 22 '15 at 19:16
  • \$\begingroup\$ Yes, your quantity is very low to get a good price on good quality parts, but keep in mind that 200 RPR359F would cost $275 US if they were available, and 200 phototransistors and 200 LEDs from reliable manufacturers, with proper datasheets, will probably be around $50 to $60 total. I presume you have access to a drill bit or shrink tube. \$\endgroup\$ – Spehro Pefhany Jun 22 '15 at 20:13
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If you search an online store such as mouser you can order the result by increasing price. On of the first results is the ITR-20002, right now at $0.50 a piece. This particular device is at the end of its lifecycle, so you don't want to use it if you plan on producing thousand of units. Since this look like a small home project, the ITR-20002 might work for you. At first glance it looks very similar to the RPR359F.

Also, if you feel comfortable with surface mount devices, you could try out the NJL5901AR-1-TE1, again among the first results of that search on mouser.

If by LDR you mean photoresistor, that can be a viable option. LDRs have higher gains than phototransistors and photodiodes, but they are slower (in the order of ms). From what I understand your application is a user interface, so milliseconds might be more than enough.

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Go on eBay. You should be able to get 100 IR LEDs and 100 IR phototransistors for less than $10. You make your table out of 1/4" plywood, with holes drilled in pairs for each sensor. 1/4" holes will work fine for 5mm components. You can fix your parts in place either with a dab of epoxy or a hot glue gun.

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  • \$\begingroup\$ What would be the material I would use to keep a separation between the IR transmitter and receiver so that the sensor get excited on by the reflected light? \$\endgroup\$ – Muhammad Ali Jun 22 '15 at 19:41
  • \$\begingroup\$ Like I said, "holes drilled in pairs for each sensor." one for the LED, one for the phototransistor. The material you drill through will do the shielding. \$\endgroup\$ – WhatRoughBeast Jun 22 '15 at 20:29
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IF you are on a frugal budget then you could try using LEDs as photo detectors I published this maybe 20 years ago the standard LEDs that were around then produced currents in the fractions of microamp range My circuits used resistors of between 1 and 10 megohm going to the base emitter of a BC547 Clearly your job is different but its worth a try

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