Hi! Am Donnerstag, 18. Dezember 2014 18:44:14 UTC+1 schrieb [email protected]: > > I am trying use the Beaglebone Black to monitor a smoke detector > activation. I have two wires coming from the smoke detector, ground and > positive lead. The voltage on the wires will go to 0.6v when the detector > is activated. I have the ground connected to the P9 header GNDA_ADC and the > positive wire from the detector going to AIN6. When monitoring the base > values of AIN6 without the detector being activated I get a wide range of > values. Example output below... >
Post more information about the sensor if you want a concrete answer. > pin AIN6 value is 2 > pin AIN6 value is 105 > pin AIN6 value is 0 > pin AIN6 value is 0 > pin AIN6 value is 687 > pin AIN6 value is 195 > pin AIN6 value is 29 > pin AIN6 value is 1799 > pin AIN6 value is 182 > pin AIN6 value is 0 > Where does these values come from and how are they scaled (ADC digits or mV)? > When the detector is activated the AIN6 value will just be above 1000. > However the random base values frequently exceed 1000 as well resulting in > a lot of false positive activations. > > My questions.. > > 1. Why is there so much variance in the base AIN values when no voltage is > being applied? Should it not be near or at zero? > 1. An open ADC input has high impedance, meaning any input will rise the signal, even with low current. The connectors and cables act like an antenna, you're receiving "Radio Erivan". -> Connect a resistor (~100 k) between the AIN-6 pin and AGND to force the signal down. (You can use the example oszi <http://users.freebasic-portal.de/tjf/Projekte/libpruio/doc/html/_cha_examples.html#SubSecExaOszi> in the package libpruio <http://beagleboard.org/project/libpruio/> to study the behaviors of the ADC subsystem.) 2. What can I do to remedy this so I can get consistently low baseline AIN > values so I do not generate false positive activations? > 2. Send a circuit diagram to get concrete answers. -- For more options, visit http://beagleboard.org/discuss --- You received this message because you are subscribed to the Google Groups "BeagleBoard" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. For more options, visit https://groups.google.com/d/optout.
