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LDR vs Ir Phototransistor

Hi  Everyone

I'm doing research for my first bot from scratch. I was hoping someone could point me to a good source of info on the advatages/disavantages of using LED & LDR vs Ir with Phototransistor for proximity sensors.

My basic goal for them is to have an edge detector in each corner and a line following array. I thought the LDRs would a simple and cheap approach but was surprised to see how cheap this Ir LED & Phototrasistor set was.

So basically effectiveness vs cost vs ease of use.

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Yup, I will pick some uo to play around with. Thanks everyone!

Unless you want to see in the visible range then IR phototransistor is the better choice. Here is a tutorial that may be useful:


Very cool thanks. What pro/cons are there to using something like the QRD1114 vs separates other than you can arrange like you did and can be found cheap on ebay?

The QRD1114 is much more compact than two separates, plus it provides a barrier between the emitter and detector so you won't get false readings or need to put a barricade between them.  The QRD1114 detector also has a filter to lessen the effects of ambient IR light.  You are able to pull the emitter and detector out of the case, so it is essentially three pieces in one (emitter, detector, and case).

I agree with Roque, the QRD1114 is a great little device. I use them on my SpurtBot, and they work great for that application.

They only work at a range of a few millimeters. If you need greater range, something like what OddBot designed in his compound eye might work.


they are 57 cents each at arrow.com, i bought a bunch and recommend them

another difference is that LDR's will be influenced by all kinds of light, whereas IR sensors will tend to ignore light
that isnt IR.

the low cost of the set might be due to it having a very short range, it seems price is somewhat proportional to range,
so considering the aplication you can just get the cheapest ones.

i recently made a line sensor module with regular LEDs and LDRs and although it sucks for various reasons,
i am definetly using IR on my next attempt.

I am aware that the LDR would be more susceptible to ambient light and need to be shrouded, I guess I'm looking more for disadvantages of the phototransistor (if any)

You should go with the LED/phototransistor pair. LDRs are slow to respond to changes in light and might hamper your line following plans.