emitter/detector

ltmhall

I think the problem maybe that the range isn't far enough. It seems the smaller the resistor that connected to the IR LED
the shorter the range. However I already have a 22o ohm in place. I also noticed that by increasing the pause value
after the LOW IR555 increases the intensity of the LED on pin 8.


Do you have any suggestions on how I can increase its range ?

Zoot

Somebody said...
It seems the smaller the resistor that connected to the IR LED
the shorter the range.

Something doesn't sound quite right. It should be the other way around -- smaller resistor = more current flowing to LED = brighter LED. Lower than 330/220 you risk burning out the LED anyway.

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ltmhall

I’m not sure what the problem is. It’s a simple circuit. ·I built the circuit and tested the Test555Frequency.bs2 program and I adjusted the 10k ohm pot until the debug terminal read 38 kHz. I even took a dmm and measured across the anode of the IR led and ground and got a frequency of 38 kHz. I will continue to keep trying to troubleshoot the circuit, but I think it works correctly. I mean if I get 38 kHz out I don’t understand what the problem could be. Is there any way to check if the signal is being transmitted through the
IR led?
·
·
I have provided a schematic of my wiring and the code I am using.
·
Any suggestions would be appreciated?
·
·
IR555 PIN 6
IRdet PIN 7

DO
HIGH IR555
IF IRdet = 0 THEN
HIGH 8
ENDIF
LOW 8
LOW IR555
PAUSE 10
LOOP

allanlane5

It could be working -- it looks like you give a "HIGH 8" for about 300 uSecs, which is WAY faster than you can see the blink. Put a 100 mSec pause after the "HIGH 8" so you can see it.

ltmhall

I tried Pause 1 after "HIGH 8" and I didn't see the led come on !

Zoot

PAUSE 1 would be 1 ms, not 100. Also, if you have video camera with "night shot" -- i.e. an infrared mode -- aim it at the IR LED and see if you can see it. You can also try putting a regular LED in place of your IR LED to see it. It sounds like your signal is OK as measured though.

Can you take a photo of your setup and post it?

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ltmhall

I tried the PAUSE 100 and I think it works. I place my hand in front and the led comes on for a few seconds and goes off.

Is there a way to increase the circuits range ? I tried switching the value of the resistor connected between
the IR led and pin 3 of the 555 and I see no difference.

Zoot

You might want to check out Robotics with the Boe-bot (or have you already?). There a number of things to change the way the IR beams out, is reflected, then detected:

- different frequencies will give slightly different ranges -- since you can tune the frequency output of your 555, you can test this out. In Robotics with the Boe-bot there is an experiment with using frequencies from 37000 - 41500 or so for differerent ranges

- the resistor between the LED and the 555 output -- try 2k -- you should have a very very short range. 330 -- a long range.

- the placement and light shield for the IR LED and the detector can influence how the IR is detected

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When the going gets weird, the weird turn pro. -- HST

Tom Walker

I just spun through this thread, so if your answer to my question is here, I apologize for not seeing it. What kind of range are you expecting to get? Driving the I/R led with 5 volts, you are probably only going to get a few inches at most. Your ambient conditions, the alignment of the emitter to the detector, the frequency of your emitter, and other factors will also determine the effective range of your setup.

What range are you looking for?

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ltmhall

I'm looking for about a inch/ 1/2 inch. The range of my circuit is only a few centimeters