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CA 95031
TEL:
800-323-3956/408-356-4186
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408-358-3799
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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
50 MHz OSCILLATOR
Bill Of Materials July 30, 1999
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