Laser Transmitter Circuit

  
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Two circuits for laser transmitters. The first uses a simple laser pointer module. Any of the normal 3 or 5mW devices will function well. Imports from the USA or Hong Kong are frequently a higher power than the UK approved units. The modules normally contain 2 or 3 1. 5 Volt mercury cells. The external modulated supply should duplicate the
Laser Transmitter Circuit - schematic

voltage used in your particular module. The electronics contained in the module will include the semiconductor laser diode and a constant current source. The ability of the constant current source to be switched on and off at audio frequency will change between manufacturers, but below 1kHz, this is not normally a problem. However, there are applications where the supply can be switched at 20 to 200kHz and voice or high speed data can be modulated onto this sub-carrier. For these high speed applications the circuit should be tested carefully with an oscilloscope. If unsuitable, the constant current source can be modified or replaced with a circuit that has a faster response. This circuit uses a crystal and a 4060 oscillator / divider to produce a square wave output in the audio range. In this case a 4MHz crystal giving 488Hz on pin 2. The 5Vp-p square wave is buffered by 3 transistors which includes a totem pole driver. I`ve used two diodesto reduce the voltage by 1. 2V which then supplies the laser module. One switch is attached to the reset pin of the 4060. This is used to select CW ( constant laser output) or Modulated CW. Another switch wired between the key input and ground allows the laser to be keyed via a phono socket or it can be switched permanently on. This is very useful when aligning the beam onto a distant receiver. Some circuits have been published using 555 timers but I felt that a crystal source would give...



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