The ADC (analog to digital converter) works by first briefly charging a small internal capacitor to the pin voltage, then disconnecting it from the pin and measuring its voltage. With high impedance on the input, the internal cap might not fully charge and also any leakage current would significantly offset the measured value. Our options are either to use smaller resistors, resulting in increased current consumption or to use a capacitor, which decreases the AC impedance without changing the DC impedance, or in other words, would absorb any small current draws with no significant change in voltage. As a side effect, the RC network will act s a lowpass filter, rejecting any ripples i the signal, which is generally a desirable thing. With resistor values in the 10kOhm's range the constant current draw will be in the 10uA's range, which is insignificant compared to the PIC's draw. The IOIO software doesn't utilize any sort of low-power sleep. So any attempt to reduce the current draw will not make a noticeable difference.
On Fri, May 22, 2015 at 4:15 PM, Andrew Robinson <[email protected]> wrote: > Could I ask what is the purpose of the capacitor in this setup. I've read > elsewhere in similar setups to use a transistor with a voltage divider as > to not waste battery by having the circuit off while not measuring, but not > sure about the capacitor. Thanks for any help. > > -- > You received this message because you are subscribed to the Google Groups > "ioio-users" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to [email protected]. > To post to this group, send email to [email protected]. > Visit this group at http://groups.google.com/group/ioio-users. > For more options, visit https://groups.google.com/d/optout. > -- You received this message because you are subscribed to the Google Groups "ioio-users" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To post to this group, send email to [email protected]. Visit this group at http://groups.google.com/group/ioio-users. For more options, visit https://groups.google.com/d/optout.
