From jlundgre@deltanet.com Tue Jun  4 13:58:30 1996
Date: Sat, 1 Jun 1996 12:04:39 -0700 (PDT)
From: John Lundgren <jlundgre@deltanet.com>

 
               Critter Ridder - Ultrasonic Sound Generator
              A Schematic - see Hands On Electronics Oct 88
           Must be viewed with monospaced font such as Courier.
 
    Legend:  ) = No Connection
             + = Connection
           All capacitors are 16V or more.
 
 
 
                 R2 same as R1              R1 1K to 10K             
       +------------/\/\/\------------------+-----/\/\/\------+      
       |                                    |                 |      
       |     C1  .0015 uF                   |                 |      
       |        ||                          |                 |      
       +--------||-------------+            |                 |      
       |        ||             |            |                 |      
       |                       |            |                 |      
       |       +---+-----------+            +-------+         |      
       |       |   |           |            |       |         |      
       |       |   |           |            |       |         |      
       |       |   \           |            \       |         |      
       |       +-> /  R8       |       R4   /       |         |      
       |           \  25K      |       10K  \       |         |      
       |           /           |            /       |         |      
       |           |           |            |       |         |      
       |           |           |            |       \         |      
       |           V        --------------------    /  R5     |      
       |    +---/\/\/\---+   \ 2  -     +  3  /     \  10K    |      
       |    |            |    \              /      /         |      
       |    |   R9 50K   |     \   7 4 1    /       |         |      
       +----)------------)------\4   op   7/--------)---------+      
       |    |            |       \  amp   /         |         |      
       |    |  D4   D3 -----      \      /          |         |      
       |  =====  1N    \   /       \    /           |         |      
       |   / \   914    \ /         \  /            |         |      
       |  /   \   or   =====          |             |         |      
       |  ----- 1N4148   |            |             |         |      
       |    |  see note  |            |             |         |      
       |    |            |            |             |         |      
       |    +------------+------------+------+------+         |      
       |                                     |                |      
       |                  D1  1N914   D2     |                |      
       |                    or 1N4148        |                |      
       |   R6  1K       |  / |     |  / |    |                |      
       +---/\/\/\----+--|<   |-----|<   |----+                |      
       |             |  |  \ |     |  \ |                     |      
       |             |                                        |      
       |             |    Q1                                  |      
       |             |    2N2222 or                           |      
       |          ------- 2N3904             R7  100 ohm      |      
       |         E/     \                                     |      
       +--------/         \----------+------/\/\/\------------+      
       |                             |                        |      
       |                             |                        |      
       |           --------          |                        |      
       +-----------|      |----------+                        |      
       |           ========                                   |      
       |           /      \                                   |      
       |         /----------\                                 |      
       |             SPKR1                                    |      
       |        piezo tweeter                                 |      
       |                                                      |      
       | -                                        9 - 12VDC + |      
                                    
 
Parts List
 
C1      .0015Uf ceramic is ok.  This cap determines frequency.
C2      .1 uF 50 V ceramic bypass
C3      100 uF 16V or more
C4      .1 uF 50V or more
D1      1N914 or 1N4148 Diode
D2      1N914 or 1N4148 Diode
D3      1N914 or 1N4148 Diode
D4      1N914 or 1N4148 Diode
Q1      2N3904 or 2N2222 or PN2222 NPN audio gen'l purp transistor
R1      1K to 10K 5% 1/4W  Just about any value will do, as long as
                           R1 and R2 are the same.
R2      same as R1
R3      1K 5% 1/4W
R4      10K 5% 1/4W
R5      10K 5% 1/4W
R6      1K 5% 1/4W
R7      100 ohm 5% 1/2W
R8      25K potentiometer
R9      50K potentiometer - trimmer is Ok if it is to
                            remain set at a fixed value.
 
 
Note:  The diodes D1 and D2 are to drop enough voltage so that the 741's
output voltage, which cannot go clear to ground, will still turn off Q1.
The frequency is controlled by R8 the 25K pot.  The R9, 50K pot controls
the pulse width of the square wave.  So this schematic illustrates how
to control frequency and pulse width independently.  R5 adds positive
feedback.                                 {J.L.}