By Ron Newton
Harry Potter had just entered a
cold, dank chamber in the tombs
of Hogwarts. His scar started to
hurt and he had a feeling of
impending doom. The chamber
was ill lit, but he barely could
make out candles on the
sacrificial altar. Harry pointed his
wand and commanded, “INCENDIO!” The candles lit. He observed a dark
foreboding figure in the corner ... it was Voldemort. His wand was raised
and pointed at Harry. Both gave their wands commands at the same time.
“INCENDIO CRUCIO!” yelled Voldemort. “STUPEFY!” cried Harry. A scream
was heard and a red light could be observed coming from the heart of ...
Who won? Well, it depends on the players.
This project builds two wands, two candles, and two badges. It uses six Microchip 12F508s. If you
don’t have a programmer, the chips are available
pre-programmed. All three of the assembly files are
located on the Nuts & Volts website ( www.nutsvolts.com).
Click on “Magazines” and then “Downloads” and look
for the issue. The schematics can also be found on the
website, along with several helpful files. The cost per set in
parts is $14 + boards. There are no small surface-mount
IR Transmitter and Receivers
One might think that you could just use a light
emitting diode (LED) and photodiode to transmit signals
for your TV and other electronics. The problem occurs if
there are any bright lights that can falsely trigger it. This is
overcome by transmitting a medium frequency, i.e., 36
kHz, and modulating this signal on and off in binary code.
This technique is known as PCM or pulse code
modulation which was discovered back in 1937. The
receiver has an input amplifier, automatic gain control,
band pass filter, and a demodulator with feedback. Not
42 December 2010
bad for a chip that costs $1.10. Once the receiver
determines that the frequency being received is at 36
kHz, it demodulates it and changes its output to a high or
low. When a signal is detected, its output is low.
Most circuits use a 555 timer for triggering IR
transmitters. These circuits require a minimum of nine
parts with a large capacitor. Each 555 has to be tuned to
the frequency of the receiver and can drift.
The Microchip PIC12F508 needs none of these extra
parts. Each of its five outputs can sink 25 milliamps and
they can be paralleled as drivers up to 75 milliamps.
Vishay has recently come out with a long range IR
detector and a high powered IR LED. The Vishay
TSAL6100 can take up to 100 milliamps continuous and
up to 1.5 amps for short periods of time.
The wand PIC12F508 uses three volts and is powered
by the momentary switch. All of its outputs are tied
together to drive the TSAL6100 IR diode at 30 kHz. It
stays on for about 70 milliseconds. The TSAL6100 was
chosen due to its high output and its narrow 10° beam.
The receivers use the new Vishay chip and have a
range of 40 meters or 120 feet (versus 10’ with the
standard TV remote) and detect the 36 kHz signal to