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USB based oscilloscope GND connection problem

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USB based oscilloscope GND connection problem

Postby nehallem » Tue Jun 14, 2016 8:19 pm

Hi, I have the 2204A picoscope, is working very well but I need to view some signals on the raspberry pi, the problem is that when I connect the ground of the picoscope to the raspberry then the USB communication between the oscilloscope and the desktop computer is lost, right after is reconnect but again right after the connection is lost again and I have this ping pong until I disconnect the picoscope GND from the raspberry. What can I do to solve this issue in order to do not burn my piscoscope, raspberry or the USB port.
Thanks in advance!
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Re: USB based oscilloscope GND connection problem

Postby Hitesh » Tue Jun 21, 2016 9:15 am

Hi nehallem,

The PicoScope is grounded via the connection to the PC. You may have a ground loop somewhere if the Raspberry Pi or something connected to the Pi is at a different ground potential.

What signals are you trying to view on the Raspberry Pi? A circuit diagram showing the connections might be helpful.

Regards,
Hitesh

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Re: USB based oscilloscope GND connection problem

Postby nehallem » Tue Jun 21, 2016 6:43 pm

Hitesh wrote:Hi nehallem,

The PicoScope is grounded via the connection to the PC. You may have a ground loop somewhere if the Raspberry Pi or something connected to the Pi is at a different ground potential.

What signals are you trying to view on the Raspberry Pi? A circuit diagram showing the connections might be helpful.

Regards,


Hi, I solved the problem with the ground, the problem was from the RPI power supply, the power supply was not isolated, now the PS is isolated by cutting the earth ground wire and it looks everything fine. Regarding to the measurement is still persist the problem, I want to decode SPI comunication but when I send something I cannot see any kind of changes even if I want to watch the SS line, or MOSI, I added a wire between MISO and MOSI to create a loopback and I receive what I send but on the picoscope there's no any reaction. If I connect the picoscope to a microcontroller SPI interface than the decode is successfully done. I used an isolated PS from manufacturing and I'm still not able to view the signals (SPI). So in my opinion I can say that the problem with the PS is solved. The SPI is configured to run at 4MHz.
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Re: USB based oscilloscope GND connection problem

Postby Hitesh » Wed Jun 22, 2016 4:14 pm

Hi nehallem,

Could you please post a circuit diagram or photo to show your setup as it could be a connection issue somewhere in your setup.

Regards,
Hitesh

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Re: USB based oscilloscope GND connection problem

Postby nehallem » Sun Jun 26, 2016 10:32 am

Hi I don't have a picture with the setup but I have just the GND from the pico connected to pin #9 and the signal wire is connected to pin #19 (MOSI) or #23 (SCLK) and there is nothing measured with the pico, if I put a wire beetwen MOSI and MISO than I receive what I send but on the pico is nothing measured.
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Re: USB based oscilloscope GND connection problem

Postby Hitesh » Mon Jun 27, 2016 11:19 am

Hi nehallem,

A circuit diagram would be helpful, including where you are connecting the probes from the PicoScope.

What settings are you using for voltage range etc.?

Regards,
Hitesh

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Re: USB based oscilloscope GND connection problem

Postby nehallem » Mon Jun 27, 2016 4:35 pm

Hitesh wrote:Hi nehallem,

A circuit diagram would be helpful, including where you are connecting the probes from the PicoScope.

What settings are you using for voltage range etc.?

Regards,

Hi, it's doesn't need a circuit diagram because the probes are connected directly to pin number 9 which is GND and the signal probes from the picoscope are connected to MOSI and CLK. That's it, there's no schematic for the moment it's just the GND crocodile from the probe connected to pin number 9 from the RPI which is GND, and the signal line from the probe is connected to MISO from RPI. al I can see on the picoscope is just noise and the V range is 5V
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Re: USB based oscilloscope GND connection problem

Postby Hitesh » Tue Jun 28, 2016 9:33 am

Hi nehallem,

Would it be possible to post a PicoScope 6 psdata file of an attempted capture so that we can see your settings and try them here?

Thanks,
Hitesh

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