Please any advice for connecting shield for my project ?

[rdpdo]

Hello everyone,

I have a project consisting of making an ADC main board with a raspeberry PI4B which will allow me to measure differential voltages from a MEMS sensor on remote micro-boards.

These boards are connected to my main ADC board with 4-wire AWG32 cables + shield. The wires transport differentials analog outputs from MEMS IC.

I wonder how to connect the shield on the side of the ADC card and on the side of my MEMS micro-cards.

Could you give me your opinion please?

Thank you !​

[Roehrenonkel]

Salut rdpdo,
 
just on one side, if on the ADC-side or the sensor-side you have to work out by yourself.
With (differential) audio-applications i connect the shield just at the input (not the source)
but with active sensors it might differ.
 
Good luck

[Terry Bites]

The shield should tie to agnd. Don't connect to the shield to ground at the remote sensor end. You don't want any power supply currents flowing in the shield.

[rdpdo]

Thanks you very much for your help !

[rdpdo]

Last question... does the order in the connector is correct ? Vcc-Vh-Vl-GND where Vh and Vl are the differential voltage ? Does it matter ? Thanks !

[coppercone2]

https://www.amazon.com/Viking-Sword-Shield-Fighting-Beginners/dp/3981162722

I assume you are looking to armor your lower body effectively?

[rdpdo]

 

[Terry Bites]

Keep your signal pair together and try and put groubd between then any an other lines.
To be honest, unless you're operating at very high frequencies and high driving impedances, crosstalk isn't usually and issue.
A few pf of stray in the connector isnt going to couple much current into your signal lines.

[rdpdo]

Good morning,

I slowly continue my reflections on my project... Even if I am an amateur I would like to make a device as clean as possible. After some readings I have made on EMI/EMC, could you give me your opinion on these ideas:

I specify that in my main card I will have 20MHz for the CLK of the SPI bus. I only have WiFI and FM/AM radio signals in my home. My sensor only sends a few 10ene of mV on the differential signals. The currents are of the order of 0.1mA.

- I plan to use an onboard battery (1.8V) in my sensors to power them rather than deporting the power supply from the main board. This way there would only be the differential signals to be transmitted which I could do on a 1 pair twisted shielded cable.

- I also plan to put my sensors in a metal shield and use an EMC metal gland to connect the cable to the shield. I plan to connect the mass of the battery of the sensor to the shield of the cable and also to the shield of the box.

- I also plan to use a battery for my main board so as not to pollute with the 50 Hz and the DC/DC choppers.

- I plan to connect the ground of the battery of my main board to the shield of the cable from the sensors but only with a capacitor so that there is no low frequency connection (and therefore avoid the ground loop) but an HF connection.

What do you think ?

[rdpdo]

My sensor is to sense acceleration.

My ADC have differential inputs so my idea is this but I dont know if it is correct ?

It multiply the number of GND and so perhaps it is a bad idea ? (I have 32 sensors)

Also, is it a problem that differential signals are not referenced by the GND in the main board ?



Else I can do that wich is less expensive by taking power from main board. In this case there is only one GND so perhaps it is better ?