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Inexpensive

I'm building a little toy, and need to read a hand-encoded storage medium something like punched tape. Right now I'm looking at the Panasonic CNB1002 reflective photosensors, which integrate an IR LED and phototransistor in a small gull-wing SMD package. In my small quantities they're about $0.55 each. I need three - a clock bit, and two data channels. Apart from the cost they're perfect - they read back well at a distance up to about 0.5mm (claimed 1mm, but my materials aren't ideal).

Is there a cheaper alternative? Discrete LEDs and phototransistors seem to be even more expensive.

I looked at CdS cells but they're also expensive-ish, and also don't respond fast enough - I want to read 256 clocks in a 1-second run, and that means about 1.5ms response time or better. Plus the varieties I've found are not well shaped for the application, as I only have one mounting surface for the illuminator and reader (but I'd be happy to be pointed at other flavors of cell, since I was fighting Digi-Key's search engine.

Reply to
larwe
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You know better than I about these things. But can you explain why you cannot consider a pair of very cheap smt LEDs or else an LED and a glass-encapsulated diode (which will respond to light?) Is it the conditioning circuitry?

Jon

Reply to
Jon Kirwan

I doubt that!

Hmm, I haven't tried using an LED as a photodetector, you know - I've only read about it. I have dozens of reels of 0805 LEDs lying around that would suffice for production for the foreseeable lifespan of this thing... I'll read up on that. Note that I need to read three at once, so it's a minimum of four, probably six LEDs. But still cheaper than a packaged device.

Thanks.

Reply to
larwe

These might not all be cheaper (especially not as cheap as using LED's as sensors!), but they're in the same ballpark as your original item. For a phototransistor you may be interested in a Sharp PT481, it has a nice small "narrow-acceptance" characteristic so it only sees through a narrowish cone in front if it, though it's thru-hole and I haven't looked for an SMT version.

The Rohm RPM-075 (found on a Freescale demo board) is SMT, but as I recall has a much wider acceptance characteristic, though you may have some "walls" between the three LED/sensor pairs to stop optical crosstalk.

The Vishay TCRT5000 IR LED/photoransistor pair (thruhole) works well too. I have only small quantities of these things, as I don't see a huge demand for line following robots...

Reply to
Ben Bradley

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