I have made strain gauge sensor with 1 strain gauge. Thet gauge is in "bottom" part of Wheatstone brigde (one strain gauge terminal is signal, second is connected to ground).
I'm using Sommer CICADA SO-D14 200-0451 cable. It's shield drain wre is connected to GND in the same spot at PCB as strain gauge wire.
Right now I'm not using any connector, but I'd like to make sensor instalation easier.
Now it looks like that:
Dark green - PCB with yellow solder points
Grey - sensor - it's just a piece of aluminium with strain gauge bonded to it. Shield drain wire is not connected to it.
Red - one strain gauge terminal (signal)
Blue - second strain gauge terminal (GND)
Green - Shield drain wire.
As I'd like to use connector I found 2 options:
- Use 2-pin connector, shield drain wire connected to gnd terminal of strain gauge at sensor side of connector, but on pcb side of connector it will be connected only to gnd at pcb. I'll use that connector close to pcb - then It will be similar situation to one which is right now.
- Use of 3 pin connector with one pin just for shield drain wire.
Will 2nd way a lot better than 1?
Connecting shield drain wire to GND at sensor side of connector is not possible (only ground point is at pcb).
Maybe there are other options?
if the shield wire is connected to the sensor ground and the Arduino ground, it is not longer a "shield", but is not a conductor. To really be a shield, do not connect it to the sensor. Then the shield will always be at the same potential as the Arduino board and really be a "shield" for the wires.
Paul
So You say I should use other ground point at PCB to connect shield drain wire?
What with situation when I'd like to use connector?
Kamool:
So You say I should use other ground point at PCB to connect shield drain wire?
What with situation when I'd like to use connector?
I am trying to say "connect the shield drain wire at ONE end only", then it will be a shield and not a conductor like the other two wires.
Paul
As I said in #1 post it's only connected at PCB side.
On drawings what I mean by green wire going into sensor body is: Sheld drain wire is going into sensor body, but is not coonnected to anything at that side.
Still...There is question about connector, how should i put that?
Kamool:
As I said in #1 post it's only connected at PCB side.
On drawings what I mean by green wire going into sensor body is: Sheld drain wire is going into sensor body, but is not coonnected to anything at that side.
Still...There is question about connector, how should i put that?
Did you check the sensor board ground and the drain wire to be sure there is no connection between the two?
IF the shield drain wire is ONLY connected to the Arduino ground and NOT to the sensor ground, then it is indeed a shielded wire. You really need a 3 pin connector if you want the shield to be effective all the way from the Arduino to the sensor.
If you break the shield at the connector, then the shield is only working from the Arduino to the connector. You can use the shield on the sensor side of the connector if you now connect the drain wire to the sensor board ground, but you have lost much of the effectiveness of the shield.
If you connect the ground wire and the shield wire at the connector, you have no reason to have a shielded wire.
Paul
Paul_KD7HB:
Did you check the sensor board ground and the drain wire to be sure there is no connection between the two?
There is connection betwee them at board.
Now it looks like that (maybe that will show it better:
R20_1 pad is for signal wire of bridge (middle part),
Top GND pad is for GND wire of strain gauge and shield drain wire
Bottom GND pad is where wire connected to vehicle battery "-" is connected.
Blue around them is copper connected to both GND pads (ground plane).
Should I add one more pad only for shield wire? How I should use ground plane in that situation? Strain gauge ground pad connected only with small trace?
