I am following in Mr. Oddbot's footsteps and once again, walking the road of cheap, IR-LED based obstical sensors. Put simply, I can not seem to replicate the results of the work of others. Let's do some bullet points:
- Want to build simple, 2 or 3 phototransisor object sensor
- Have been folowing This Post both to the letter, and with many variations
- I am basically (no, actually) remaking the Dagu Compound Eye, but smaller and "on edge"
- For bench testing, I am using only one "set" of parts (1-4 IR LED's, 1 or 2 Phototransistors, one ADC)
Problems:
- The Compound Eye works incredibly well, indoors it can catch my hand 10" (25cm) away.
- I have replicated the Compound eye's circuit exactly (each part matching the specs of the parts used on the C.E.) but I cannot get the ADC numbers like the Compound eye. My set-up has maybe 5" (13cm) range, with a total output fluctuation of maybe 1v. I.e. 2v -3v total range from nothing in front to white paper 3cm away.
Tried/Questions:
My first question is why the NPN phototransistor is on the "top" of the circuit. Is there an advantage to this location? In every schematic I see, we have collector to 5v+ and the emitter to a pull-down and ADC. Every other NPN-thing I have ever done had the collector going to the ADC/Pull-up and the emitter going to ground. Why is this different?
What's up with the transistors? I used countless "general purpose" transistors in my tests (the tests above were done with no transistors) and I could see no effect in the output. I went through 2222's, 3904's, 4401's and a darlington chip. All worked (and I know we are talking a volt/current issue here as well as impedence issues) but I could see no change in output on the O-scope or ADC numbers by adding a transistor. The total range of voltage outputted was basically the same as a straight output of the phototransisor when using say, a 2n2222. It seemed to be performing the task equally well with or without this "amplifier" circuit.
To finish this off, I basically tried every configuration of this kind of sensor. Pull-ups, pull-downs, transistors, transistor-to-transisitor-to-transistor set-ups, pull-up/down resistors from 1k to 10M, etc. etc, etc. --All in all, I could not seem to do better than this 5" (13cm) range nor did I ever see the kind of numbers I can see from the compound eye. What the hell am I doing wrong, and how do I make a simple R/L or R/C/L IR obstical sensor? Sheesh! I used to know how to do this kind of stuff.
--You guys using magic parts or something, Oddbot?