Hi I am wondering if anyone has experienced the same phenomena as we have or could provide an explanation.
We are testing the ADC of the TelosB platform using a signal generator connected directly to the TelosB ADC ports( we are using channel ADC1). We generated a 1kHz ramp signal sweeping from 50mV to 100mV which we then capture with the Telosb mote. For reference voltage we used Vref and Vss in the ADC configuration interface. We are also using the ADC conversion formula found on page 347 of the MSP 430xx1 user's guide (section 17.2.1 12-bit ADC Core). After receiving the ADC integer value at the mote we convert it back to voltage BUT we noticed that for every run we always see twice the amount of voltage that was supplied. For instance if we supplied a ramp signal from 50mV to 100mV, we see on the mote (after conversion) 100mV to 200mV ramp signal. We have double checked the conversion is correct AND we have tried both the 2.5v and 1.5v reference voltages and seen the same phenomena on both settings. Has anyone else seen this or can explain why the voltage seen at the mote is multiplied by a factor of 2? Does the Telosb have a built in operational amplifier? Ernest McCracken Research Assistant Networking Research Laboratory http://netlab.cs.memphis.edu Computer Science Department University of Memphis
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