• 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 my Handbook of Optical Through the Air Communications.  Note: The LF357 op amp is no longer available, this circuit is for reference only.

• 30KHZ LIGHT RECEIVER AMP
  This circuit uses NPN darlington transistor to amplify the signal produced from short light flashes, as detected by a PIN photo diode.  The circuit draws only about 330uA from a 6v battery.

• 40KHz LASER BURST DETECTOR
  This circuit was originally designed to detect weak flashed of laser light bounced off of a fabric video projection screen. It was used as part of a firearm training system. It generates a 100mS output pulse whenever it detects a 3ms to 5ms-laser burst, modulated at 40KHz. It is very sensitive and could be modified for long-range laser communications.

• 40KHz Light Detector with High Ambient Light Immunity
  This circuit is designed for detecting infrared light modulated at around 40KHz.  It’s feedback scheme cancels much of the DC component from ambient light.  It’s conversion factor is about 100 millivolts per microwatt of 900nm light.

• 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.

Dave's Light Detector Circuits:   Page 1, Page 2, Page 3, Page 4