Hi all,
I am working on a project where I need to transmit a series of pulses at 50% duty cycle by IR. The transmitter is composed of a 555 astable oscillator which sends its output through an IR LED, and that works just fine. The receiver is giving me no end of trouble, however. Using an unamplified photodiode or phototransistor the signal is getting through but so weakly the range is only a few inches (unsurprising w/o amplification). So I tried using a transimpedance amplifier set up as follows:
At up to about a foot range, I can measure the appropriate signal (which varies between 2.5 and 50 kHz) across the 91k resistor, but with an amplitude of only a few millivolts. I can't measure any voltage signal being generated at Vout with respect to ground. My understanding is that the amplifier is supposed to produce a voltage at Vout that is the product of the photodiode current and the 91k resistance, but this does not appear to be happening. Also, why is my range so limited? I have four decent sized IR LEDs in series so I thought I would get decent range. Can anyone tell me what I'm doing wrong, or recommend another way of amplifying an IR signal? Thanks very much.
I am working on a project where I need to transmit a series of pulses at 50% duty cycle by IR. The transmitter is composed of a 555 astable oscillator which sends its output through an IR LED, and that works just fine. The receiver is giving me no end of trouble, however. Using an unamplified photodiode or phototransistor the signal is getting through but so weakly the range is only a few inches (unsurprising w/o amplification). So I tried using a transimpedance amplifier set up as follows:
At up to about a foot range, I can measure the appropriate signal (which varies between 2.5 and 50 kHz) across the 91k resistor, but with an amplitude of only a few millivolts. I can't measure any voltage signal being generated at Vout with respect to ground. My understanding is that the amplifier is supposed to produce a voltage at Vout that is the product of the photodiode current and the 91k resistance, but this does not appear to be happening. Also, why is my range so limited? I have four decent sized IR LEDs in series so I thought I would get decent range. Can anyone tell me what I'm doing wrong, or recommend another way of amplifying an IR signal? Thanks very much.