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1. 

   Fullback
   Member

   Hello everybody

   I have got many maple mini rev3 boards as logic units for a wireless sensor network. I have got a problem with the ADC; even if I use a stabilezed voltage source, the maple board is not able to properly sample it. I provide 2.7 V, and i have tried to sample it with different maple mini boards and with all the analog input pin, but I have got different reading for every sampling.

   The configuration is has follows: a maple mini connected via USB to my laptop ( I have used both a mac and win XP pc ), a stabilezd and constant voltage connected on one of the ain pin of the board.

   The code is has follows:

   const int sensorPin =7;
     int  reading;
   
     void setup() {
           pinMode(sensorPin, INPUT_ANALOG);
   }
   
   void loop(){
           reading=analogRead(sensorPin);
           SerialUSB.println(reading;)
   }

   I have used this simple code in order to understand whats wrong..

   additional info:
   I have measured the voltage across ground pin and sensor pin, with a kehitley potentiometer (it is a precision instrument) and i have got the right reading.

   maple IDE v 0.0.12

   Any suggestions?

   Thanks

   Posted 1 year ago #
2. 

   gbulmer
   Moderator

   Fullback - is this exactly the code that you are using?

   If so, it contains a syntax error, and does not compile.

   This line has the ';' in an incorrect place:
   SerialUSB.println(reading;)
   the ';' should be after the ')'
   SerialUSB.println(reading);

   Posted 1 year ago #
3. 

   manitou
   Member

   common ground?

   Posted 1 year ago #
4. 

   gbulmer
   Moderator

   Ah, good point manitou.

   Fullback:
   Have you connected the stabilised power supply to the Ain pin and AV- (analogue ground)?
   Could you measure from a battery source (to the analogue pin and analogue ground), to avoid any other ground influence?

   When you say "even if I use a stabilezed voltage source, the maple board is not able to properly sample it"
   What values do you get?

   Posted 1 year ago #
5. 

   Fullback
   Member

   @ gbulmer: "SerialUSB.println(reading;)" it is a typing error sorry.

   I do not connect the analog ground, to the ground of the stabilized voltage source, in order to avoid ground loop. But i just tried and it works. THANKS

   Posted 1 year ago #
6. 

   okie
   Administrator

   To avoid the problems caused by ground loops, which is having induced voltages across and currents through a conductor that is suppose to be equipotential, make good, solid connections between grounds or any conductors that are suppose to be equipotential. A good connection can mean many connections so that there's lower resistance in some situations, while in others, it's better if connections are made in a hierarchical way so that there are little islands of non-interacting peace. If there's fairly low resistance connection between EITHER the GND net or the 3.3V net on the Maple and one of the potentials involved in the the voltage measurement you would like to make, then you probably won't get what you like. For me, the most enlightening resource on ground planes, return currents, impedance lines, high-speed or high-power and/or low-noise PCB layout, and more, was and is a book called Electromagnetic Compatibility Engineering by Henry Ott.

   Posted 1 year ago #

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