title: Beaglebone Black sampling rate too slow and gives false voltage libpruio
body: <p>I'm pretty much a noob when it comes to this kind of thing, so if you guys could either help me or direct me to a place to learn what I need to know, I would greatly appreciate it.</p>
  
  <p>Basically my problem is that I am using the libpruio library to continuously sample analog values from the board. 2 things are going wrong here. </p>
  
  <p>The first is that whenever the BB is sampling the voltages, the voltage of the wire that is hooked up to the AIN pin goes up. I've observed this through hooking up an oscilloscope to the same wire the pin is sampling. What I see is that whenever the BB starts sampling, the entire signal (just a sound wave from an amplified mic) is shifted up .8-.9 volts. This is also reflected in the values that I get from the BB, which are around 30,000 (when they should be 0). Hooking the pin up to ground gets me 0, which is correct, and hooking it up to 1.8 volts gets me something like 65520, which is also correct. So maybe it has something to do with the signal being weak?</p>
  
  <p>The second issue is that even though I am receiving values at a rate of like 500khz-900khz, the actual rate seems to be around 11khz. What I mean by this is I only get a new value every 88us, and the rest of the values I get are stay the same as the new value until the next 88us passes, when I get a new value. These times correspond to the voltage shift up, which I mentioned in the previous paragraph. So actually what I see on the oscilloscope is that whenever I sample with the BB, there is a saw wave, with the frequency at the 11khz I was mentioning earlier. </p>
  
  <p>In conclusion, whenever the BB samples, it first increases the voltage at the pin by .9volts, takes a sample of that voltage, and the voltage dies down for the next 88us, all the while the BB spits back the sample it took at the beginning of the period. I do not want this. I want it to not affect the voltage significantly, and take new samples every time the code runs.</p>
  
  <p>As for the code I'm using, it's basically a slightly modified version of the IO_Input example in the libpruio library, with the values being stored in an array for later use instead of being printed immediately.</p>
  
  <p>If you guys need any more information, I will gladly post it here, but for now I'm wondering if it is something super obvious that I'm missing.</p>