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Circuits Designed by Dave Johnson, P.E. : |
- OPTICAL RFID
TEST CIRCUIT
I designed this test the concept of using light techniques to send identification
data instead of RF. A more detailed discussion on this scheme can be found in the
Imagineered new products section.
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- SINGLE IC
FORMS SENSITIVE MODULATED LIGHT RECEIVER
The circuit uses a very inexpensive C-MOS IC that is connected to a small
photodiode. Using an unique inductive feedback network, the circuit provides high
sensitivity under high ambient light conditions. It is a great circuit when you want
to extend the range of an optical remote control transmitter.
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- SIMPLE
NITROGEN SPARK GENERATOR
Nitrogen or air sparks are very powerful light sources that produce flashes that
last only a few nanoseconds. This line powered circuit generates a continuous series
of very small sparks across electrodes with a 0.05 inch gap.
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- VOLTAGE TO
FREQUENCY CONVERTER + 1uS LED PULSE DRIVER
This circuit receives the signal from the above amplifier and launches powerful 1uS
infrared light pulses from a low cost LED that are frequency modulated by the audio
information. The 10KHz center frequency of the pulse stream is low enough so a
standard infrared LED can emit ten times more light than conventional long pulse
techniques. The circuit is described in more detail in the transmitter section of
Dave Johnson's
Handbook of Optical Through the Air Communications. (this link is off-site)
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- XENON
LAMP FLASH DETECTOR
This circuit uses a small 2.5mm square photo diode in conjunction with a 100mH coil
to detect the short light flashes from a xenon lamp. The coil makes the
circuit immune to normal room lights. Its 10mv sensitivity can detect light
flashes from a range of over 100 feet. Reflections from a room’s walls and
ceiling is usually enough to trigger the circuit. The entire circuit draws
only 3 microamps from a 6 to 9 volt battery.
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