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From: Lizard Blizzard
Subject: Re: IR repeater using Sharp GP1U59
Date: Thu, 17 Oct 2002 13:21:03 -0700
User-Agent: Mozilla/5.0 (Windows; U; Windows NT 5.0; en-US; rv:1.1) Gecko/20020826
X-Accept-Language: en-us, en
Bob the Builder wrote:
> "Bob Nelson" wrote in message news:...
>>I recently aquired a few of these IR detection devices and I was wondering
>>if anyone had any experience with these or could help with a design to
>>repeat the ir signal. I'm a total novice with circuit design but can follow
>>a schematic. I'd like multiple inputs repeating the signal to multiple ir
>>Here's the device:
>>Here's the inside:
>>email: bylogic at lycos dot com
> I've used the Sharp IR detector / decoders before. The units contain a
> photodiode, amplifier, limiter, bandpass filter, demodulator,
> integrator, comparator, and an open collector output transistor. The
> device receives an on-off modulated IR signal (typically 40kHz) and
> outputs a signal representing the On and OFF periods. For the ON
> period, the output is LOW, for the OFF period, the output is weakly
> pulled up to the supply voltage (about 100K Ohms). In order to repeat
> the IR signal as demodulated by this device, it is necessary to
> re-modulate it at the desired frequency. The accuracy and stability
> requirements of the system define the type of oscillator needed. The
> simplest method is to use a CMOS 555 timer IC connected as an astable
> mulivibrator (oscillator) tuned to the desired frequency (typically
> 40kHz). Modulation is accomplished by using the output of the Sharp
> device to drive a logic level P-channel MOSFET (gate) connected to +5V
> (source), and the anode of an IR LED (drain). The cathode of the IR
> LED is connected to one end of a current limiting resistor (47 Ohms or
> so). The other end of the resistor is connected to a logic level
> N-Channel MOSFET (drain). The source is connected to ground (+5V
> return). The gate is connected to Pin 7 of the CMOS 555 timer IC and
> to one end of a pullup resistor (4.7k). The other end of the resistor
> is connected to +5V. Pins 4 and 8 of the 555 are connected to +5V, pin
> 1 is ground. Pin 3 is connected to a resistor (17.86k Ohm, use 5k Ohm
> trimmer in series with 15k Ohm) whose other end is connected to pins 2
> and 6 as well as a capacitor (0.001uF). The other end of the capacitor
> is connected to ground. Pin 5 has no connection. This configuration
> gives 50% duty cycle at a frequency determined by; f=1/(1.4*R*C).
> In this way, the IR LED will be turned on by the N-CH MOSFET at a
> frequency controlled by the 555, but only when the P-CH MOSFET is
> turned on by the output of the Sharp device being low (IR signal
> signal present).
> A similar oscillator circuit is shown in:
> If higher accuracy and stability is required, a crystal controlled
> oscillator/ divider could be used. A 74HC4060 is a possibility.
Or better yet, forget about all this foolishness of demod and modulation
and just use a simple amplifier, like the following.
This is the circuit that you want to build. It has to be tuned, and if
you have two different appliances on differente freqs, then it won't
work with both appliances. That sucks.
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