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• 40KHz Light Detector with Sunlight Immunity  NEW
  The circuit below was designed to turn on an external 12v relay, whenever it detects light from a nearby LED light source, modulated at 40KHz to 50KHz.  This circuit was originally designed to operate from a fast moving vehicle. The light transmitter was positioned at a stationary position, while the matching receiver was mounted on the vehicle.  The circuit has high ambient light immunity and in most cases, can operate in direct sunlight.

• 40KHZ LIGHT RECEIVER AMP
  This circuit is similar to 30KHZ LIGHT RECEIVER AMP but provides more gain and operates up to 40KHz.  However it draws more power supply current.

• 40KHz LIGHT RECEIVER IS IMMUNE TO AMBIENT LIGHT
  If you want even more sensitivity than the above circuit, try this design. When used with a one centimeter square photodiode, you can achieve a range of several hundred feet with a standard TV or VCR remote control module.

• 40KHz MODULATED LIGHT DETECTOR
  This circuit uses a unique cascode amplifier circuit to convert the current from a PIN photo diode to a current without any feedback network. It is very stable and very sensitive. The circuit shown has the potential for a conversion factor of 10 volts per microwatt at 900nm. I included a simple JFET post-amplifier with a gain of about 20.

• 40KHz TV-VCR LIGHT SOURCE REPEATER
  This circuit is designed to be placed directly in front of a standard TV or VCR remote. The exiting light pulses produced by the circuit match the pulses from the remote but are about 10 times more powerful. Using the device, the remote can operate a TV or VCR over three times the normal distance.

• 1uS LIGHT PULSE RECEIVER PLUS POST AMP
  This circuit is designed to detect very weak light pulses lasting 1uS. It uses a tuned LC feedback network to provide high sensitivity while giving high ambient light immunity. A post voltage amplifier is included with a gain of about X20. The circuit is described in more detail in the receiver section of Dave Johnson's Handbook of Optical Through the Air Communications. (this link is off-site)