I am outputting a 40kHz square wave from arduino and passing it through an RC circuit in order to get a clean 40kHz sinusoid out. However, the output wave I am getting is noisy.(see picture) Any advice on how to get rid of noise?enter image description here

  • \$\begingroup\$ Show how/where you measured it. \$\endgroup\$ Mar 27, 2018 at 22:04
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    \$\begingroup\$ How/where have you earthed the scope probe? Those spikes are almost certainly the edges from the square wave, getting into your measurement somehow. \$\endgroup\$
    – user16324
    Mar 27, 2018 at 22:06
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    \$\begingroup\$ Move the ground probe to the filter part of your circuit. You are getting logic noise into your probes. \$\endgroup\$
    – user105652
    Mar 27, 2018 at 22:07
  • \$\begingroup\$ Did you choose the wrong parts and layout? \$\endgroup\$ Mar 27, 2018 at 22:09
  • \$\begingroup\$ You're probably utilizing the Arduino's Digital GND pin, which truthfully, is not the best common to use. \$\endgroup\$
    – user103380
    Mar 27, 2018 at 22:30

1 Answer 1


Radiated or Conducted?
True error or measurement error?

Ground shift ? probing error**? induction loop current , capacitive coupling?

Also avoid long grounds on scope probe gnd loop near switched inductive sources.

For a 10:1 probe** ground lead , 10cm is too long. Best Test Eng practise is by removing gnd clip and probe tip and use twin test points to tip pin and barrel. If not avail make them with resistor wire leads by cut and solder as test points.

Or get the accessory for the probe or make one. enter image description here

Use twisted pair for all sources of interference and use low ESR caps on Supply. Use braided or heavy ground conductors.
Keep wiring short and neat.

Show schematics and photo of possible source and of interference.

  • \$\begingroup\$ Thanks for the replies, that mat be a grounding issue. I guess I first need to make sure the square wave is clean, I'll give it a try \$\endgroup\$ Mar 27, 2018 at 22:35
  • \$\begingroup\$ it's not the square wave but the rather the ground and radiated induced transients with high impedance. Probe close to output for signal and Analog ground or directly across cap in the case of a passive filter with pins 1cm apart using exposed probe tip. \$\endgroup\$ Mar 27, 2018 at 22:41

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