🚀 go-pugleaf

In article <10955@goofy.Apple.COM> hunter@apple.com (Kurt Hunter) writes:
-Does anyone know of a discrete or integrated amplifier circuit that can be 
-used to increase the signal of an IR detector diode while preserving all 
-the IR signal data?
-
-What I want to do is detect both the IR signal data pattern and it's 
-carrier frequency as a TTY logic level signal.  I believe typical data 
-pattern frequencies are in the range of about 45ms, while carrier 
-frequencies have a range of about 30kHz to 80kHz.
-
-I'm also thinking I will need some filtering in addition to amplification, 
-however, I don't want the filtering to block out the carrier frequencies.  
-I've been told there are some commercial IR pre-amplifier products that 
-amplify, filter and wave-shape an IR signal from a directly connected IR 
-detector, unfortunately, these same products also demodulate the signal's 
-carrier frequency and that's not what I'm after.  Any suggestions?
-Kurt Hunter                             e-mail: hunter@apple.com

I refer you to the March 1987 issue of BYTE magazine pg. 113. Steve Ciarcia
Has a design for a trainable master remote controller. Instead of trying
to do the carrier frequency and pulse detection in analog he samples the
IR signal at a 1 Mhz rate and uses a microcontroller to examine the sample
for the carrier and pulse lengths.

I find it's a much more workable method than all the discrete electronics
because most of the work is done in software instead of hardware.

He uses a simple LM311 comparator circuit to boost the signal and then 
shifts the data into a sift register at 1 Mhz. The shift register is read in 
every 8 microseconds. By taking 32 or so 8 bit samples and analysing them you 
can determine both the carrier frequency and the pulse widths.

I'm in the process of trying to build a circuit along the same lines.
I'm using the TL414 phototransistor and a high power IR LED from Radio
Shack. I'm trying to build a IR copier using the sampling principle.
I plan to detect with the phototransistor, amplify with the LM311 circuit,
sample with a shift register and then drive the IR LED. I'm hoping to
be able to copy the incoming signal with enough precision to drive the
box the original remote drives.

Anyway if anyone is interested I'll send mail and let you know how it
came out.

BAJ
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Another random extraction from the mental bit stream of...
Byron A. Jeff - PhD student operating in parallel!
Georgia Tech, Atlanta GA 30332   Internet: byron@cc.gatech.edu