Help a pH.D. scientist: Infrared sensor

Hydro, in response to your question about the minimum resistor value, it depends on which IR LED you ended up getting. Going back through the thread I couldn't figure out which one you ended up getting, so here's how you figure it out:
minimum resistance = (9V-Vled)/Iled
where
Iled = maximum current through LED (from LED spec sheet) and
Vled = voltage drop across LED (from LED spec sheet)

So if you got the matched pair from radio shack (2V drop at 40mA (edit: these values from the website appear to be inaccurate)) the minimum resistance would be 175 ohms. Though if you pulse it on and off you can probably cut that in half.

I just checked the Radio Shack package for the IR pair. For the LED the V-fwd is 1.3V to 1.7V. The maximum "continuous" I-fwd is 150mA.

ken

hydrocynus said:

I am not currently using the LM311 but the LM741.

Click to expand...

Then you'll be forever plagued with problems.

The 741 is an old op-amp, not a comparator, use a comparator such as the LM311.

Hi again,

Did he get tired of working on this already?