• on Test & Measurement
  • Published in issue 4/2008 on page 56
About the article

Frequency Response Sweep Oscillator

50 Hz - 100 kHz range using the Parallax SX28 micro

Frequency Response Sweep Oscillator
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.
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Gerber file

CAM/CAD data for the PCB referred to in this article is available as a Gerber file. Elektor Members can exclusively download these files for free as part of their Membership. Gerber files allow a PCB to be produced on an appropriate device available locally, or through an online PCB manufacturing service. Elektor recommends its business partner Eurocircuits as the company of choice for its own prototypes and volume production in selected cases.

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
C1 = 10µF 40V radial
C2 = 100µF 40V radial
C3-C6 = 100nF
C7 = 100µF 25V radial
D1 = LED, 3mm, low current
IC1 = 7805
IC2 = SX28AC/DP (Parallax), programmed, Elektor Shop # 070951-41
IC3 = AD822AN
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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