I think I understand now. So: 1. If you're really intending to measure a signal as high as 30A, the output voltage will be around 4.5V, which exceeds the range the ADC is willing to accept (0-3.3V). 2. Unless the sensor has a built-in amplifier, it is likely that it has a fairly high output impedance. 3. To address both of the above problems, I recommend conditioning the signal using one of more opamp stages, so that it has about 1.5V bias and about 1.5V amplitude @ 30A (or 50mV/A). 4. The IOIO samples at 1kHz. There should be no problem sampling of a 60Hz signal. Moreover, since you know it is a sine wave, all you really need is measure the peak-to-peak voltage which you can then trivially convert to RMS. I suggest that you look at the buffered version of AnalogInput, so that you don't miss or depend on your application thread loop frequency.
On Wed, Jul 15, 2015 at 7:15 AM, Julio Castellanos <[email protected]> wrote: > Hi Ytai, thank you for your help. The signal is the output of an A.C. > current sensor, the frequency is the same as the network, 60 hz, and the > sensor can measure up to 30 A with a sensitivity of 66 mV/A. The signal has > always a D.C. value of 2.5 V so if i measure 1 A the signal will have a max > of 2.566 V and a min of 2.434 V. The absolute maximum with 30 A is 4.48 V > and absolute minimum of 0.52 V, so the signal is always in the range of the > analog input of the ioio. I want to know the value rms of the current in my > smartphone, and i tried obtaining the rms of the voltage by calculating the > max value of a buffer of 1000 values and the multiplying it by 0.707. I get > the value rms of the current with an accuracy of +-0.1 A, but i need it to > be less than that, that's why i though it would be better to compute the > rms value of the signal in hardware so i dont have to send the whole buffer > of the signals. > > El martes, 14 de julio de 2015, 18:44:30 (UTC-5), Ytai escribió: >> >> Before we begin, can you please specify the signal you're trying to >> measure better? >> Specifically, its min and max (instantaneous) voltage, and its bandwidth >> would be important. >> Based on that I can recommend a way of measuring it. >> >> On Tue, Jul 14, 2015 at 3:06 PM, Julio Castellanos <[email protected]> >> wrote: >> >>> Hello, i'm currently working with the IOIO analog input with a sensor >>> signal that comes out as an A.C. signal in the range of 2,5 V as mean >>> value. I've tried to get the voltage through the analog input and get the >>> rms value in software, but the value changes to much because of the >>> bandwith limit of the IOIO:Android communication. I'm now looking to get >>> the RMS directly in hardware and just send that value to the software but i >>> gave a look at the hardware code for adc.c and i don't understand almost >>> nothing, can someone point out to me a source where i can learn how does >>> this code works? >>> >>> -- >>> 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. > -- 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.
