Fred said:
I assume LED0 is the IR transmitting IR LED. I suspected it may have
flashed at least the once bearing in mind that you have a 27R series
resistor and a power supply of 12V. This would give a current of 3-400mA, 3
to 4 times rated current.
Infrared LEDs are often rated for a maximum of 100mA continuous forward DC
current. If the circuit is working properly like it should, then the signal
detected from the remote will be a roughly 38kHz 50% duty cycle squarewave
carrier frequency light signal that is further modulated by the data at
likely less than 50% duty cycle (of the 38kHz carrier) at some frequency
well below the carrier. Usually IR remotes will AM modulate the 38kHz
carrier at some frequency so slow as to be very easily human detectable as
flickering.
So the effective duty cycle the LED should see is likely less than 25%, but
certainly well less than 50%. So even though the 27 ohm resistor limits the
current to something like 3-400mA, when multiplied by the effective duty
cycle the average current through the LED will likely be somewhat less than
100mA. If the circuit is operating properly, the LED will not be
significantly abused...
Unfortunately this circuit is very poorly designed in many respects. The
circuit has novel simplicity, but pays for it in functionality/reliability
and performance.
If the ambient lighting conditions are too high, the circuit will constantly
detect that and turn the output stage on full blast at 100% duty cycle
(plain DC). Thus there certainly exists a real possibility the IR LED could
be damaged by excessive current.
The other really serious problem is the circuit doesn't really try very hard
to keep the incomming and outgoing duty cycles the same. This is probably
why the OP's implementation isn't working. While some IR receiver circuits
might have lax input filters that will respond acceptably to a distorted IR
signal, the OP's IR receiver probably doesn't like the distortion that
likely will be added by the circuit. As a result is balks and doesn't work.
A better designed IR repeater would do something more like this:
An infrared 38kHz receiver IC (such as the Panansonic PNA4602M from Digikey)
should first detect the remote control signal. Since the output of the
receiver IC will be demodulated data, we will need to remodulate the data
onto a new 38kHz carrier. Since the output of the Panasonic is an open
collector output with internal pull up resistor, the output is inverted from
the sent signal. We will need to invert the output signal to get it looking
right again.
A 38kHz 50% duty cycle (fairly high precision, +/-1kHz will likely start
reducing functionality) oscillator will be needed. The oscillator output
should be ANDed with the output of the inverted IR receiver IC output. The
final output should be buffered by a fast switching small MOSFET such as the
BSS138 to drive the LED at pulse currents of up to around 400mA (or perhaps
more if you can insure the average current is less than 100mA). Using
bipolar junction transistors isn't necessarily a good idea for this stage
since they can have fairly long storage times which will distort the signal.
At 38kHz and reasonable drive currents the effect may be minimal, but to be
safe it is easier to just use a MOSFET. Make sure the range extender LED is
not pointed such that any significant amount of IR light will fall on the
detector, otherwise signal feedback will occur and the system will probably
self oscillate.
Even when going to all this trouble the range extender may still not work
since the Panasonic PNA4602M or similar IR receiver IC may distort the
signal enough to cause problems in some cases. In these instances probably
the easiest solution to increasing range is to modify the remote control
itself. Replace the IR LED with one that is more efficient (such as the
Vishay TSAL6100 from Mouser), or use multiple LEDs in parallel (make sure to
pump up the driver power to drive them properly).
To give an idea of what is possible, using six paralleled TSAL6400 LEDs
pulsed at 1A peak currents and a Vishay TSOP1256 receiver IC I was able to
achieve outdoors (at night) data transmission at distances of up to an
estimated 70 meters. Even more range is surely possible with shorter beam
angle LEDs (or more LEDs) and perhaps some other circuit tweaks/improved
optics.
