On 5/6/2014 3:28 PM, Mark Ruys wrote: > On two different BBB's (latest revision) I've noticed strange behavior of > AIN4. I have a TMP36 (analog temperature sensor) running on 3V3. Vout > measures 712 mV ((712 - 500) / 10 C = 21 degree C). If I attach Vout to any > AIN* except AIN4, I can use the BB and read out 712. So the ADC is working, > as is the TMP36 sensor. > > As soon as I connect Vout to AIN4, the voltage drops from 712 to 673 mV and > slowly decreasing. Why is this? Is another part of the BBB already using > AIN4 and is it reserved? > > No other capes or anything else connected to P8/P9.
Make sure you have the touch-screen (ADC) driver configured properly. There are internal FETs that drive voltage onto various AIN lines in order to sense resistive touch screens with no other external components. If the driver is turning any of these FETs on, they could be working against your external temperature sensor, which may be slowly decreasing it's output voltage as the output drive transistors heat up. See the Technical Reference Manual for details on the drive FETs hooked to the AIN pins.. -- Charles Steinkuehler [email protected] -- 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.
