+ User Manual
Analogue inputs
The AM335x processor has an integrated Analog to Digital Converter that can be used as touch
screen controller and as general purpose ADC. This converter is called the TSCADC hereafter.
Because of erratic behaviour of this converter
with the 3.2 kernel, the original BeBoPr had
the option to mount an extra ADC for more accurate results. With the BeagleBone black and
the 3.8 kernel performance even got got worse, so the the extra 12 bit converter is now
standard on the + boards, until a software solution is found. This converter is called
the ADS1015.
Both ADCs operate in parallel on the same signals and either one can be used for the
application.
Signal Conditioning
Some signal conditioning is done before feeding the analogue signal to the ADCs. For a proper
understanding of the transfer function, the input circuit of the first thermistor is shown
drawn in illustration 7. The same circuit is available on all analogue inputs. VCLAMP and
PWR_THRM0 are low impedance sources. VCLAMP is 3.4 Volts and PWR_THRM0 is twice the
reference voltage of the AM335X ADC.
† Some driver problems have been identified but there's probably also a hardware problem. The original
BeagleBone had a lot of noise on the conversion results, with the BeagleBone Black the situation became
worse. Conversion results seem to suffer from large delays, irregular failure and some kind of cross-talk.
version 1.4.9 (09/04/14)
page 25
Illustration 7 - Analogue Input