Remote connection to Memsic 2125

drm

Hello,

I've attached a Memsic 2125 to a programmable microcontroller. And, I'm able to obtain the expected data when the accelerometer is attached via 6 inches of wire. But for this particular project, the sensor needs to reside 3 feet from the microcontroller.

I soldered connectors to 3 feet of CAT 5 cable and reconnected the Memsic. But, with the 3-foot run of cable, the readings suddenly slow down. (Periodically, they'll speed up to my original setting of 4 readings per second; but, for the most part the readings are extremely slow (> 1 second per reading).)

If the readings were consistently slow, I'd assume that the cable run had introduced problematic resistance. But, because the readings are periodically normal, I'm baffled/puzzled by the behavior.

I wondered if anyone on the forum had suggestions as to how I might trouble-shoot and resolve the issue?

Thanks!

kwinn

The output signal from the Memsic is a pulse whose duration is proportional to the acceleration, and the currents involved are so small that the resistance of 3 feet of wire is insignificant. I don't really see how the wiring can affect the rate of the readings since the Memsic will output a pulse every 2.5 or 10 milliseconds depending on the factory programming. I would be more suspicious of the software, but to be certain the wiring is not the problem I would suggest the following:

1- Connect power and ground to the Memsic using one twisted pair of the cat5.
2- Connect each signal using a twisted pair, with the ground connected only at the Memsic or Microcontroller end, not both ends.
3- Make sure all the connections are good.
4- Check the power supply for the correct voltage and no ripple or other noise.

Use a scope to check power and signals if you have one available.

Phil Pilgrim (PhiPi)

I would also terminate the signal lines with maybe 4.7K (or smaller if the Memsic can drive a stiffer load) to ground at the microcontroller end.

-Phil