Pages: [1]   Go Down
Author Topic: Accelerometer attached to 1m cable  (Read 703 times)
0 Members and 1 Guest are viewing this topic.
0
Offline Offline
Newbie
*
Karma: 0
Posts: 5
Arduino rocks
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

Hello folks!

I'm trying to read values from an accelerometer that is attached to a 1m (unshielded) cable. The Serial Monitor shows values that go up and down like crazy. Is it possible to read values from a cable that is that long or is there simply too much noise on that distance?

Regards,
Tschiggi
Logged

Massachusetts, USA
Offline Offline
Tesla Member
***
Karma: 212
Posts: 8966
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

Not all accelerometers are the same.  What signals are passing through the wire?
Logged

Send Bitcoin tips to: 1L3CTDoTgrXNA5WyF77uWqt4gUdye9mezN
Send Litecoin tips to : LVtpaq6JgJAZwvnVq3ftVeHafWkcpmuR1e

Anaheim CA.
Offline Offline
Faraday Member
**
Karma: 47
Posts: 2925
...
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

and do you have Vcc well bypassed at the device as well? a serious but frequently by-passed idea, perhaps in haste? I do hope with an external PSU and not the umbilical...

Doc
Logged

--> WA7EMS <--
“The solution of every problem is another problem.” -Johann Wolfgang von Goethe
I do answer technical questions PM'd to me with whatever is in my clipboard

Offline Offline
Edison Member
*
Karma: 9
Posts: 1016
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

A digital signal (I2C, SPI) could be a problem.
You could use an accelerometer with analog outputs. A few meters of cable would only introduce noise to the analog signal, but would not disturb any digital communication.
Logged

0
Offline Offline
Shannon Member
****
Karma: 215
Posts: 12455
Arduino rocks
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

Definitely too long for standard fast logic like SPI, for an open-collector bus (like I2C) you can try decreasing the value of the pull-up resistors to 2k2 (no smaller) which might help.  Also adding 100 ohm resistors _in series_ with the SDA and SCL lines at either end should reduce ringing.

For long wires like this carrying logic signals you _must_ use either shielded cable or (better) twisted pairs (each pair one signal wire and one ground wire).  (This increases the chance of getting it to work and more importantly stops you running an illegal radio transmitter!)

Considering shortening the wires to 30cm where things are likely to just work.

And yes you _must_ have decoupling directly at the accelerometer (probably already on the breakout board though).

For analog signal you might want to add 1nF capacitors to ground at the receiving side to reduce RF and noise pickup (and longer wires less of an issue).
Logged

[ I won't respond to messages, use the forum please ]

Pages: [1]   Go Up
Jump to: