Newbie accelerometer wiring question

[sonictext]

Hi everyone,

I have an adxl193 analog accelerometer (http://www.sparkfun.com/products/9332) that I am trying to interface with a phidget i/o board (http://www.phidgets.com/documentation/Phidgets/1011_0_Product_Manual.pdf).

I am having trouble calibrating the signal because the acceleration is (zero-g_reference_signal - signal)/sensitivity and the zero-g reference signal is VCC/2. However, VCC is not constant - I assume since it is powered by USB.

I would like to now use an external 5v power supply. I can see the signal on the oscilloscope when I connect the power supply. Unfortunately, the phidget is not detecting the sensor. I am completely wiring ignorant ---

VCC and GND on the accelerometer are connected to +5v and grn on the power supply while OUT on the accelerometer is connected only to A1 on the phidget ----- VCC and GND on the phidget are not connected to anything.

Does anyone have any advice? I am electronics ignorant.

Thank you.

 

[vk6kro]

It looks like, from the first diagram, that the power is obtained from the USB port of a computer. This gives a 5 volt and ground supply.

So, you would have to find the power supply points on the circuit board and run new wires to these from an external power supply.

As there is a strong possibility of wrecking the circuit if you use a variable power supply, I would feed the input via a 5 volt regulator, so that there is less chance of getting more than 5 volts on the circuit.

If you are unfamiliar with wiring circuits, you should probably just use it as it was intended or you may do damage to the Phidget or the computer.