Electronic – TIP-Barrel test of oscilloscope

groundoscilloscope

I am trying to measure the noise at the output of my buck regulator. I am getting some ripples. I feel that the ground loop caused by my oscilloscope GND ref might have a small impact here.

I was thinking of approaching this via the tip-barrel approach. Now, I wanted to know if I need specialised probes for the TIP-Barrel approach.

Now, the probe has a met section shown in the image above. Is that GND?
If yes, in the tip-barrel approach, is it ok if I just connect a wire from here to my GND reference in the PCB?

This is shown in the image below. Will just a piece of wire from here to my PCB act as a GND?

Best Answer

Yes, that metal section of your probe is ground, and yes, minimizing loop area when probing fast signals is good.

If you're probe didn't come with one of those nice little ground springs as shown in the second picture, yes, you can build a makeshift one with a small piece of wire. Keep the wire as short as possible, and keep the distance between the point you are probing and ground as close as possible i.e. ground the probe to the closest ground on the board.

Edit:

I went hunting for ground springs, since I realized that I actually had no idea if you could buy them. The most common term is "ground spring", or sometimes "short ground clip", and individual replacements can typically be found by searching " ground spring" or similar. For instance, Digikey has the following (among others):

BK Precision 5mm ground clip, set of 4 3.6USD, but they're not in stock.
Teledyne Lecroy ground pin 8USD for one, but they're in stock.

Related Solutions

Electronic – Cannot get a digital square wave on oscilloscope from the GPIO of the Raspberry Pi

There are a couple of issues with your code that can be easily fixed. First, you are calling wiringPiSetup which means you will need to refer to the pins by their WiringPi designation which can be found on this page:

https://projects.drogon.net/raspberry-pi/wiringpi/pins/

You are then setting pin 7 (wiringPi designation) to be an output which is actually GPIO 4 (physical pin 7) and not the CE1 pin as you mentioned. CE1 would actually be wiringPi pin 11.

The next problem is in the while loop. You are doing a digitalWrite on wiringPi pin 4 (not 7 as you configured) and are always setting it low so it would never toggle high even if configured correctly. The following code should be what you are looking for but is not tested. This assumes you want to use CE1 which is normally used for SPI but should work with WiringPi as an general I/O pin:

  if (wiringPiSetup () == -1)
    exit (1) ;

  pinMode(11, OUTPUT);

  while(1) {
    digitalWrite(11, 0);
    digitalWrite(11, 1);
  }

Why does the GND of the Arduino oscillating as well

I don't think your ground rail is oscillating. You may be able to test whether it's oscillating relative to the voltage rail by connecting the ground clamp to ground and the probe to the 5v or 3v rail for your Arduino.
Voltage isn't like current: you can't measure it at a point, it's almost always the difference between two points in the circuit. When you remove the ground what exactly you're measuring becomes somewhat ambiguous. What you're most likely to see is the distorted AC component of the signal at the probe mixed with a weak 60Hz (or 50Hz in some places) distorted sine wave from the mains power in the building and any other AC signals near the probe.

Best Answer

Related Solutions

Electronic – Cannot get a digital square wave on oscilloscope from the GPIO of the Raspberry Pi

Why does the GND of the Arduino oscillating as well

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