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From: sasrer@unx.sas.com (Rodney Radford)
Subject: A very STABLE 40khz generator (was IR receivers)
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Date: Mon, 10 Jan 1994 14:56:51 GMT
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>>Why, oh, why are people still using this 70's component?
>I noticed you didn't suggest a substitute. I did have a good suggestion
>to use schmidt inverter with a resistor from front to back and a cap to...

    [ ... info on methods to generate 40khz signal ... ]

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).


--
---
Rodney Radford          || Computer Graphics/Imaging
sasrer@unx.sas.com      || SAS Institute, Inc.
(919) 677-8000 x7703    || Cary, NC  27513

