A very STABLE 40khz generator

(Circuits -> InfraRed)
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(From Rodney Radford)

A circuit that I have used before is based on the CD4060 (14stage binary counter) and a 640Khz ceramic resonator. The CD4060 is basically an oscillator and a ripple counter to divide the 640khz down to something more usable.

Here is the pinout of the CD4060 (frequencies are assuming a 640khz input signal into pins 10/11/12 - circuit shown below):

               +-\/-+
      160hz  1 |    | 16  Vcc
       80hz  2 |    | 15  625hz
       40hz  3 |    | 14  2.5khz
      10khz  4 |    | 13  125hz
      20khz  5 |    | 12  \
       5khz  6 |    | 11   >---- see sub-circuit below
      40khz  7 |    | 10  /
        GND  8 |    |  9  NC
               +----+

Sub-circuit for a 640khz ceramic resonator:

      12 >----------------------+
                         740pf  |    (you may be able to obtain
      11 >-------+----+---|(----+     a resonator with builtin
                 |    |         |     capacitors and three leads)
        640khz  ---   \         |
         res.    O    / 1Mohm   |
                ---   \         |
                 |    |         |
      10 >-------+----+---|(----+
                         740pf  |
     GND >----------------------+

A nice part about this circuit is that it delivers a STABLE 40khz signal, as well as delivering several other frequencies that can be used to modulate the 40khz carrier. For example, the person that designed this circuit (Ken Boone, member of Triangle Amateur Robotics) used it to build several beacons in his yard to serve as navigation points for a robotic lawnmower. By diode-OR'ing the results of the 40khz carrier and one of the lower frequencies (such as the 125Hz) line to drive a ring of IR-LEDs, he could locate the beacon and tell which, of several, beacons he had found.

This circuit has proven to be VERY stable, and is fairly inexpensive (about $1.50 for the CD4060 and 640Khz ceramic resonator).


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