Address:  P. O. Box 1457, Los Gatos, CA 95031
 TEL:      800-323-3956/408-356-4186
 FAX:      408-358-3799
 Mobile:   408-858-4528
 URL:      www.dsmith.org
 Email:    doug@dsmith.org

This page contains the schematic and circuit board pictures of an oscillator that can be built out of common parts for just a few dollars. It has a good square wave output from a few MHz to about 60 MHz using an HC240 chip as the oscillator. The design only uses half the 8 buffers on the chip, so you could actually build a dual oscillator from a single chip. The HC240 chip can be purchased for about 50-80 cents from many sources. If you are having trouble finding any of the parts, send me an email. One source that should have all of the parts is  Mouser Electronics.

When building the oscillator, the main parameter to watch is lead length (read that "inductance"). Note in the bottom view of the circuit board, the direct, point-to-point wiring. The loop consisting of the potentiometer, switched capacitors, the 100 Ohm resistor, and pins 2 and 18 has its area minimized by layout of the components.

Let me know if this design is useful to you. I have been using it for almost 10 years in my seminars. If you have been to one of my seminars, you have seen this oscillator driving the experiments.

Thanks to Abe Riazi <ariazi@anigma.com>, who contributed a bill of materials (BOM) generated from the schematic below. It is included at the bottom of this page with some modifications and additions.
 
 
 

        Oscillator Schematic
 
 
 

          Top View of Circuit Board
 
 
 

          Bottom View of Circuit Board
 
 

 Item  Quantity  Reference             Part
____________________________________________________________

   1       1        C1       22 pF, 50 V, Ceramic Disc
   2       1        C2       680 pF, 50 V, Ceramic Disc
   3       1        C3       470 pF, 50 V, Ceramic Disc
   4       1        C4       220 pF, 50 V, Ceramic Disc
   5       1        C5       100 pF, 50 V, Ceramic Disc
   6       1        C6       47pF, 50 V, Ceramic Disc
   7       1        C7       22 uF, 35 V, Axial Electrolytic
   8       2      C8, C9     0.33 uF, 35 V, Tantalum
   9       1        D1       1N4001 Rectifier Diode
  10       2      J1, J2     BNC, chassis mount, female
  11       1        R1       100 Ohm, 5% , 1/4 W
  12       1        R2       Potentiometer, 500 Ohm cermet,
                             single turn
  13       2      R3, R6     47 Ohm, 5% , 1/4 W
  14       2        R4       3.3 K, 5% , 1/4 W
  15       1        R5       150 Ohm, 5% , 1/4 W
  16       1       LED       LED Indicator
  17       1                 LED Socket
  18       1        U1       HC240
  19       1                 20 pin DIP Socket
  20       1                 Circit Board (2.75" x 3.75"),
                             Archer part no. 276-158A
  21       1       SW1       DIP Switch, 4 positions

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