IR emitter detector

[roboninja93]

hello
for the IR sensor what is the output voltage in dark condition?
if R2 is around 10k and then what would be the output voltage in dark conditions?
please help...
thanks

[joe61]

hello
for the IR sensor what is the output voltage in dark condition?
if R2 is around 10k and then what would be the output voltage in dark conditions?
please help...
thanks

That depends on how bright your emitters are, how sensitive your photo transistor is, what "dark" means to you, etc.

As a general answer though, since you're going to be reading the values with an ADC, print the values you get to a display of some kind, graph them or whatever.

If you want a formula, someone more math aware than I am can probably give you one if you (as Soren would say) eliminate the adjective and provide some numbers.

Joe

[Soeren]

Hi,

If you want a formula, someone more math aware than I am can probably give you one if you (as Soren would say) eliminate the adjective and provide some numbers.

Hehe, this one can be done without numbers, assuming dark means no light (whatsoever), as this would, for any practical purpose, remove the photo transistor from the equation and if the input impedance of the A/D-C is sufficiently high (like at least R2 x 100 or 1M), it really doesn't matter either, so it's Vcc with R2 in series, but with no significant loading = Vcc (or at least within 1%).

That is just not very interesting, when it comes to real life use, but I'd suggest roboninja93 went and read the recent postings about the subject (does people ever search the forum?) as a starter:
http://www.societyofrobots.com/robotforum/index.php?topic=15028.0

[roboninja93]

yeah I had read the tutorial but didnt see the topic on the forum but saw now...
I have one doubt
in light conditions the transistor's resistance is less so we get low voltage  but since we have used the resistance R2 higher than the resistance of the transistor in dark condition how would we get the output close to maximum?
or would would be somewhere close to half of Vcc(i.e. 5V)?
thanks

[Soeren]

'Hi,

I have one doubt
in light conditions the transistor's resistance is less so we get low voltage

Yes, the more light, the lower the output.

  but since we have used the resistance R2 higher than the resistance of the transistor in dark condition how would we get the output close to maximum?

R2 is not higher than the resistance of the photo transistor in dark condition - if totally screened from light, the transistor will be completely off (= extremely high resistance).
What the resistance will be, with the LEDs on, but over a dark (non-reflective) surface, depends on the specific photo transistor and you'll have to measure the voltage and adjust R2 if needed - I thought you read the other thread?

or would would be somewhere close to half of Vcc(i.e. 5V)?

Only when the photo transistor equals R2 will it be at 2.5V
Perhaps read the other thread once more and then experiment, experiment and experiment - that's how you get the connection between theory and real world application.

[roboninja93]

yeah i got it... we have to adjust the value of R2 to get proper output according the light conditions...
thanks