1 Jul
2010
1 Jul
'10
11:44 p.m.
> I susptct it's actually more like what you
said later... If you have a
> digital camera around, you can use it for this, but it's not necessirily
Actually, thinking back to when I rebuilt the CX printer (early 1990s), I
don;t think digitial cameras were common then. CDD image sensor analogue
camcorders existed (and were well-known to have a responsie in the near
IR), but were not excatly cheap. People who had them would use them to
detect IR output from remote cotnrols, but nobody would buy one for that
purpose alone.
I have never tried on of those IR detector cards -- can you still get
them. They are a card about the size of a credit card coated with a
special phosphor. You 'charge it up' by exposing it to normal visible
light, and then when IR hits it it give a visible glwo. Sold for checking
remote cotnrol handsets, I bit it would detect the beam in a laser
printer too.
the best tool
for the job, and it's probably not worth getting one solely
to use as an IR dtector.
Quite so! I've only used one for that because it was
immediately
available at the moment of need. something much simpler and smaller using not very
many components which
would serve as well or better. Actually probably quite a lot better as
When I was setting uphe CX scanner, I used a simple remote control tester
that I'd built from a Mpalin kit. A photodiode driving a 3 transisor (I
think -- it's certainly discrete transistors, no ICs) amplifier, driving
an LED. The amplifier is AC coupled, so it responds well to the
flickering IR output of the average TV remote control. too, though. :-) I happen to have several old
"hermetically sealed"
0-1ma meters and though it would make the "display unit" unnecessarily
large I somehow find the idea of using one of those as the output
indicator appealing somehow. I'm probably just pipe-dreaming a way to
The Maplin tester is entirely qualitiative. If it gets IR, the LED turns
on. You can get some idea if a remote control handset is going weak by
seeing how far away you can detect it, but nothing more.
I think gettting any sort of meaningful scale on a meter would be very
hard. The chartacterisitics of the photosensor are probably not that well
known (at least not for cheap sensors). Making an IR photometer is a much
harder project :-)
finally use one of those. Of course there's no
real reason not to use
both if desired - might take 1 more transistor at most or maybe just a
couple of current divider resistors - pump say 0-10ma through the LED
and 1/10th of that through the meter. Something like that...
Shunt the meter suitably (a resistor of 1/9th the resistance of the meter
coil) and put it in series with the LED?
-tony