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40KHz Voltage to Frequency Converter
This circuit was designed to frequency modulate a 40KHz carrier, using human voice frequencies. A common flip/flop is used at the core of the circuit.
200MHz - 400MHz VOLTAGE controlled OSCILLATOR
If you need a clean emitter coupled logic (ECL) type signal between 200MHz and 400MHz this circuit works fine. It uses four voltage controlled capacitors to change the frequency.
Air Transparency Monitor, Xenon Flash Receiver
I designed this circuit many years ago to monitor the quality of a mile long column of air for future optical communications experiments. The transmitter system (circuit 72 below) uses a
powerful xenon flash in conjunction with a large 12 inch fresnel lens at the transmitter end and a matching 12 inch lens with a PIN photo diode at the receiver. The receiver system was
connected to a weather station and a computer to collect the changes in intensity of the light flashes under different weather conditions. It has the potential for a 30+ mile range. I
have also used this system to conduct cloud bounce experiments.
CMOS SCHMITT TRIGGER IC MAKES VCO
By changing the supply voltage fed to a classic 4584 Schmitt trigger type oscillator, the oscillator frequency can be changed over a range of 50:1. A 74HCU04 inverter is used at
the output of the 4584 to maintain a constant TTL logic level signal.
Light to Frequency Converter
This circuit uses a CMOS version of the classic 555 timer, to form a light intensity to frequency converter. A small PIN photo diode is used as the light detector. The pulses
produced are short, so in some applications you may want to stretch them or feed them through a flip/flop to produce a square wave signal. Although the circuit shown is designed
for a 5v supply, it could operate from almost any voltage from 3v to 15v.
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 my Handbook of Optical Through the Air Communications.
Wide Band Zero Cross Detector
This circuit was designed to convert a low amplitude 40KHz signal into a clean square wave signal. It will work with inputs as small as 5mv peak-to-peak or as large as 3 volts peak
to peak. The input frequency can range from a few kilohertz to about 150KHz.
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