Answered: Accelerometer Wiring Question

I just got the accelerometer yesterday in the mail. I started to wire it up; put the analog inputs with the other analogs on the Vex (1 - Gyro, 2-4 - Line, 5-7 Accelerometer).

The silk screen on the chip shows the ‘B’ or ground near the edge of the unit and the wiki says the ground is indeed is near the ‘B’ side. That sounds right. However, the picture shows the ground (Black wire) on the other side. Hmm.

If I wire like it says on the web page then no code can be downloaded; it appears the serial port becomes inop. If it wired like the picture, then the code can download, but the values don’t change.

I’m using RobotC 1.54beta and using SensorValue[accel_x] to read the accelerometer.

Could use some assistance and clarification on the wiring. Is the silk screen wrong or is the picture wrong?


The WiKi is correct, the black wire goes on the side where the “B” is silkscreened on the Accelerometer and it should be connected to an Analog Input. You should then be able to read the values on the Analog Input.

Well, that leaves the other half of the question then. When I connect the PWM cable (straight thru) from the Accelerometer to an Analong Input the Vex refuses to communicate with the PC and the VEX gets rather warm rather quickly. (Black wire toward the B and black wire to the exterior side of the VEX)

Also, this photo clearly shows the cables in backwards:

I’m kind of stuck on this one, not knowing if my Accelerometer is bad or the Vex is bad.


**If you can read High on the Analog Port with nothing connected to it and read a Low with a Vex Jumper installed on that Port, then the VEX Microcontroller is Ok and you we need to call us (903-453-0802) for a RMA for the return of the Accelerometer.

Also, we have updated the picture.**

Just want to make sure I did this test correctly.

Using the Device debugger I observed the following. I used the same pwm extension wires that I used with Accelerometer in the same ports.

Port 5, 6 and 7 - Reads zero w/out the jumper and -510 w/ jumper.


What value you actually see will vary depending on the code you are using. The fact that you see a large different between having a Jumper and No Jumper is a good indication that the port is working correctly. Using the easyC On-Line Code, a typical reading on the Analog Port is over 900 with no Jumper and 0 with a Jumper installed.

Seems to be about right. I’m using RobotC for this project. It certainly seemed like they were reasonable values. Now, I’ve never really needed to use the jumpers so I’m not sure if there is a polarity to them; the negative number was a little suprising, but I suspect that it’s an artifact.

The odd thing about connecting the Accelerometer is that it completely shuts communication down through the serial port, you can see the timers, debugger, etc. just halt when it’s plugged in and continue when it’s removed.

I think I’m going to take this one to the phones from here on out. We can probably close up this thread unless you think it needs to stay open.


The VEX Jumpers connect the 2 outer pins together, thus the Signal line is connected to Ground on the VEX Microcontroller.