Frequency Response Sweep Oscillator
50 Hz - 100 kHz range using the Parallax SX28 micro
Published in issue 376, April 2008
This project found its origins in a need to see and measure the frequency response of audio filters, tone controls and amplifiers in real time. An SX28 microcontroller module from Parallax turned out to be a really good means of implementing the circuit. The author developed this circuit as a means of displaying the frequency response of a circuit on a standard oscilloscope. The firmware for the microcontroller core of the test instrument is written in assembly language.
Resistors
R1 = 1k
R2-R6,R9,R11,R12,R13,R15,R17,R19,R20-R23,R27,R29 = 10k 1%
R7,R8,R10,R14,R16,R18,R24,R28,R30 = 20k 1%
R25 = 1M
R26 = 110
P1 = 5k preset
Capacitors
C1 = 10µF 40V radial
C2 = 100µF 40V radial
C3-C6 = 100nF
C7 = 100µF 25V radial
Semiconductors
D1 = LED, 3mm, low current
IC1 = 7805
IC2 = SX28AC/DP (Parallax), programmed, Elektor Shop # 070951-41
IC3 = AD822AN
Miscellaneous
S1-S5 = pushbutton, 1 make contact
S6,S7 = on/off switch, 1 contact
S8 = switch, 1 changeover contact
K2-K6 = BNC socket
K7 = 4-way SIL pinheader
X1 = 50MHz ceramic resonator
SX28 source and hex files, free download # 070951-11.zip
PCB, ref. # 070951-I from www.thepcbshop.com
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Click below to download a PDF copy of this article from Elektor magazine. Please note. In view of the complexity of international markets, Elektor cannot guarantee the availability of components for this project.
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