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Sharp GP2Y0D810Z0F Digital Distance Sensor 10cm

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light sensing  strikes me as one of the more interesting and important aspects of robot design. ive had some experience with couple dozen different photosensor setups and settled on 3 types: basic led/phototransistor, modulated emitter/receiver, and photo resistor.

ir leds are cheap and can be run from dc. for basic short range sensing matching phototransistors like tops030 can use a digital input. this is good  if mcu pins are scarce and close proximity (1-2cm). for example dohyo edge sensing. adc inputs can also be used for limited distance sensing because the phototransistors have analog output. not really long range though.  these are somewhat low cost averaging around a dime ea.

for longer range hooking that led up to a pwm port bit and using ir demodulators like TSOP4838 can provide much longer range. orders of magnitude in some cases. 10cm in direct sunlight to 10-20 meteres in dim. the output is digital so even though frequency is fixed around 38khz tricks like pulse width modulation of the led can be used for distance info. properly collimated good for object detection. power rail filtering mandatory. sensors a little more expensive at 50 cents but same cheap ir led as previous.

photoresistors (ldr) are much slower but very cheap (5 cents) and regular red or green leds can be used. they make good photo interrupters and edge sensors but because of the wide spectrum and lack of lens not so good for object/distance. however i found this last characteristic, when coupled with a red & green led, useful for color detection which the other types fail miserably at. almost as good as a camera video system for my m&m sorter but about 1% the cost.

with all the above methods cf or black paper tube shroud is very helpful to minimize saturation and increase directionalty. typically order of magnitude improvement in useable distance. a little dab of black fingernail polish also helpful to fine tune for ambient light conditions. i do tend to prefer diy approach using discrete  components rather than integrated off the shelf to keep cost down. im sure others have their own favorite devices and circuits but these work for me.


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