I bought an old used analog oscilloscope last week. Our home has no ground, so my oscilloscope is not grounded and shows my high-frequency (example 16 MHz of XTAL) wave superimposed on a 50 Hz sinusoidal.

I think this happens because my scope is not grounded. How can I ground my scope when there is no ground in the home? Are there alternatives for electrical grounding?

In fact, I connect the scope's ground and signal to 2 pins of 16 MHz Arduino XTAL. I saw 16 MHz very noisy sinusoidal wave on scope, I played with trigger level so much to decrease the noise but not effected, and when I changed the time division to ms range, I saw 16 MHz sine wave ride on 50 HZ sine wave . Is it possible my scope was faulty or damaged?

  • 3
    \$\begingroup\$ Do you know for a fact your home is not grounded? Or are you guessing from your scope reading? I really doubt your home is not grounded even if in a developing country, though I could be wrong. Is your ground clip actually working? What happens if you just try and measure the voltage across a battery in auto-run mode? Or what happens if you just clip your probe and ground clip together? \$\endgroup\$
    – DKNguyen
    Sep 14, 2022 at 18:55
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    \$\begingroup\$ I'd be more concerned about a lack of ground on your home wiring before trying to get the scope reading correctly. \$\endgroup\$
    – Andy aka
    Sep 14, 2022 at 19:42
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    \$\begingroup\$ People have been known to float their scopes on purpose. A dangerous practice, especially when the scope ground is connected to a hot mains. The scope should work fine, show us exactly how you connected it. \$\endgroup\$
    – Mattman944
    Sep 14, 2022 at 20:17
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    \$\begingroup\$ Yes I'm sure that our home was not grounded, in new buildings about from 10 years ago the grounding became obligatory. Maybe 80% of homes not grounded. I connect the ground of scope to ground of the circuit. Is it possible my scope was faulty or damaged? \$\endgroup\$
    – hadi
    Sep 15, 2022 at 11:00
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    \$\begingroup\$ I estimate that hundreds of thousands of Swedish homes are not grounded, and Sweden is hardly a backwards low-tech nation. However, that doesn't mean my scopes display junk. I can't test with my PM3295 though, since its PSU is broken. \$\endgroup\$
    – pipe
    Sep 15, 2022 at 11:26

1 Answer 1


You should not connect scope ground and signal to the two crystal pins.

Scope ground should be connected to MCU ground pin so you can probe one crystal pin with one probe.

  • \$\begingroup\$ I went to test it \$\endgroup\$
    – hadi
    Sep 15, 2022 at 11:37
  • \$\begingroup\$ I tested it and it worked. Of course, I should have put the probe in 10X mode before testing the 16 MHz frequency, right? \$\endgroup\$
    – hadi
    Sep 15, 2022 at 12:55
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    \$\begingroup\$ Yes. As a rule of thumb, use 10x mode by default, unless you know you need/want/must use the 1x mode. \$\endgroup\$
    – Justme
    Sep 15, 2022 at 13:00

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