So I'm working with more IR type circuits and need to detect an IR signal reliably at long distance in strong sunlight. I've tried many things to make the typical 38kHz IR receiver modules work better in strong ambient light. I've had some success, but it's always at a cost, like reduced fields of view. I've read that the best method is to use a photo-diode and filter out the DC (ambient compent) using some type of inductance filter.
So I started hitting the books again to brush up on RL, RC, and RLC type circuits. Then I came across this circuit:
http://www.discovercircuits.com/H-Corner/40khzlight.htm
I'm a little confused. I understand that the first inductor from the left is mainly just sending the DC component of the ambient light to ground leaving the AC component to go through the coupling capacitor to the amplifier. What I'm confused about is the parallel RL circuit between the power supply and the Darlington pair. How is that going to ensure that the 40kHz is amplified? I have formulas for series RL circuits, but this is in parallel. Can a parallel RL circuit act as a bandpass filter? And how do I calculate the center frequency and the Q?
Thanks.
So I started hitting the books again to brush up on RL, RC, and RLC type circuits. Then I came across this circuit:
http://www.discovercircuits.com/H-Corner/40khzlight.htm
I'm a little confused. I understand that the first inductor from the left is mainly just sending the DC component of the ambient light to ground leaving the AC component to go through the coupling capacitor to the amplifier. What I'm confused about is the parallel RL circuit between the power supply and the Darlington pair. How is that going to ensure that the 40kHz is amplified? I have formulas for series RL circuits, but this is in parallel. Can a parallel RL circuit act as a bandpass filter? And how do I calculate the center frequency and the Q?
Thanks.