Re: XO-1.5 audio input DC mode
Excerpts from Sascha Silbe's message of Wed Nov 17 19:38:20 +0100 2010: I'm trying to use the XO-1.5 as an oscilloscope, using xoscope (*) [1]. [...] Thanks to everybody who replied and helped me figure this out. I still haven't succeeded using the XO-1.5 as an oscilloscope, but made some progress: 1. The totally strange values I see in xoscope are a software issue. If I run it using alsa-oss (instead of relying on the kernel-level OSS compatibility layer), the values are sane. However it now keeps hanging for long periods of time (many seconds). 2. The voltage I see with bias off is probably generated internally by the codec chip. I don't think the chip designers envisioned it to be used without a decoupling capacitor. I've been told the (non-public) data sheet is rather sparse on details about the analog part of the chip, so this is a good an understanding as we're going to get. Unless someone finds a magic way to disable this from the digital side of the chip (which I doubt), we'll have to cope with it. This means that we need an external buffer circuit in order to prevent the XO-1.5 from feeding voltage back into the measured circuit. 3. I have managed to build osqoop [3,4] and fix the most obvious bug that prevents its usage on high-resolution displays. Like xoscope, it still uses OSS (instead of ALSA), but apparently in a different enough way not to trigger the same bugs (or cope better with whatever OSS does differently than xoscope expects). The sampling rate and resolution is fixed to 16bit @ 44.1kHz (the hardware claims to do up to 24bit @ 192kHz). Like Measure, there is no support for calibration. The UI is based entirely on voltage levels, so you'll get fake voltages that have no relationship to the input voltage. 4. The problem with the right channel probably was a bad cable. I'll check this once I got osqoop running well enough. The schematic of the analog audio circuitry on the XO-1.5 is now available on the wiki [1,2]. Sascha [1] http://wiki.laptop.org/go/Hardware_specification_1.5#Integrated_peripherals [2] http://wiki.laptop.org/go/File:Ext_audio_1.5.png [3] http://www.eig.ch/fr/laboratoires/systemes-numeriques/projets/osqoop-l-oscilloscope-libre/index.html [4] http://gitorious.org/osqoop/pages/Home -- http://sascha.silbe.org/ http://www.infra-silbe.de/ signature.asc Description: PGP signature ___ Devel mailing list Devel@lists.laptop.org http://lists.laptop.org/listinfo/devel
Re: XO-1.5 audio input DC mode
On 11/24/2010 06:52 AM, Sascha Silbe wrote: 2. The voltage I see with bias off is probably generated internally by the codec chip. I don't think the chip designers envisioned it to be used without a decoupling capacitor. I've been told the (non-public) data sheet is rather sparse on details about the analog part of the chip, so this is a good an understanding as we're going to get. The datasheet is sparse yes but we have technical contacts at conexant who can answer your questions. The DC input mode was part of our early discussions with them and its supposed to work at least as good as the last chip did. I specifically remember asking them about this and telling them it was something to test in our early reviews of the hardware. It should work. If not then we need to know why so we can prevent it from happening on the 1.75. If you will frame up your questions with good detailed descriptions on how to duplicate the problems you are having I'll see that it makes it to conexant for testing and feedback and make sure they have the proper hardware to test it on. -- Richard A. Smith rich...@laptop.org One Laptop per Child ___ Devel mailing list Devel@lists.laptop.org http://lists.laptop.org/listinfo/devel
Re: XO-1.5 audio input DC mode
On Wed, Nov 24, 2010 at 6:52 AM, Sascha Silbe sascha-ml-reply-to-201...@silbe.org wrote: 2. The voltage I see with bias off is probably generated internally by the codec chip. [...] Unless someone finds a magic way to disable this from the digital side of the chip (which I doubt), we'll have to cope with it. This means that we need an external buffer circuit in order to prevent the XO-1.5 from feeding voltage back into the measured circuit. What is the impedance of your input? What's the capacitance? I can see getting some leakage current into a high-impedance high-capacitance circuit, but for most purposes this shouldn't really be a problem. --scott -- ( http://cscott.net/ ) ___ Devel mailing list Devel@lists.laptop.org http://lists.laptop.org/listinfo/devel
Re: Re: XO-1.5 audio input DC mode
This sounds like the problem with TurtleArt The bias is present in voltage mode. The version for sensors on the xo1.5 is http://bugs.sugarlabs.org/attachment/ticket/2506/TurtleArt-104.xo The bias is not leakage and capacitance, 15k ohms at the socket halves the bias voltage at the socket. It is not necessarily the same issue though, could be in the turtleart code, amixer code or hardware. Tony On Wed, Nov 24, 2010 at 6:52 AM, Sascha Silbe sascha-ml-reply-to-201...@silbe.org wrote: 2. The voltage I see with bias off is probably generated internally by � the codec chip. [...] � Unless someone finds a magic way to disable this from the digital � side of the chip (which I doubt), we'll have to cope with it. This � means that we need an external buffer circuit in order to prevent the � XO-1.5 from feeding voltage back into the measured circuit. What is the impedance of your input? What's the capacitance? I can see getting some leakage current into a high-impedance high-capacitance circuit, but for most purposes this shouldn't really be a problem. --scott -- � � � � � � � � � � � �� ( http://cscott.net/ ) ___ Devel mailing list Devel@lists.laptop.org http://lists.laptop.org/listinfo/devel _ This mail has been virus scanned by Australia On Line see http://www.australiaonline.net.au/mailscanning ___ Devel mailing list Devel@lists.laptop.org http://lists.laptop.org/listinfo/devel
Re: XO-1.5 audio input DC mode
I see a problem recording sound in the Distance activity, but I don't know if it is related. You can see more information in OLPC #10122 http://dev.laptop.org/ticket/10122 The sound was recorded with the internal mic, at the start there are a negative max and a curve before you can get values to process (http://dev.laptop.org/attachment/ticket/10122/Screenshot.png) Gonzalo On Wed, Nov 24, 2010 at 11:41 AM, Richard A. Smith rich...@laptop.org wrote: On 11/24/2010 06:52 AM, Sascha Silbe wrote: 2. The voltage I see with bias off is probably generated internally by the codec chip. I don't think the chip designers envisioned it to be used without a decoupling capacitor. I've been told the (non-public) data sheet is rather sparse on details about the analog part of the chip, so this is a good an understanding as we're going to get. The datasheet is sparse yes but we have technical contacts at conexant who can answer your questions. The DC input mode was part of our early discussions with them and its supposed to work at least as good as the last chip did. I specifically remember asking them about this and telling them it was something to test in our early reviews of the hardware. It should work. If not then we need to know why so we can prevent it from happening on the 1.75. If you will frame up your questions with good detailed descriptions on how to duplicate the problems you are having I'll see that it makes it to conexant for testing and feedback and make sure they have the proper hardware to test it on. -- Richard A. Smith rich...@laptop.org One Laptop per Child ___ Devel mailing list Devel@lists.laptop.org http://lists.laptop.org/listinfo/devel ___ Devel mailing list Devel@lists.laptop.org http://lists.laptop.org/listinfo/devel
Re: XO-1.5 audio input DC mode
On Thu, Nov 25, 2010 at 02:54:33AM -0300, Gonzalo Odiard wrote: The sound was recorded with the internal mic, at the start there are a negative max and a curve before you can get values to process (http://dev.laptop.org/attachment/ticket/10122/Screenshot.png) Vague memory this is privacy related; so that the microphone is not immediately active without the LED showing some indication for enough time for the operator to see it. XO-1 too. -- James Cameron http://quozl.linux.org.au/ ___ Devel mailing list Devel@lists.laptop.org http://lists.laptop.org/listinfo/devel
XO-1.5 audio input DC mode
Hi! I'm trying to use the XO-1.5 as an oscilloscope, using xoscope (*) [1]. I thought that should be easy to do given that the audio input seems to be specifically designed to do something like this. However my experiences so far are strange at best... For a start there always is a bias voltage. I can reduce its impedance from ~ 15kΩ to ~ 5kΩ and increase it from ~1.75V to ~2.5V, but never turn it off. I also don't understand the values I am seeing: It's always oscillating with half the sampling rate. The Capture level seems to affect both the base line and a partitioning into several value ranges. E.g. for level 39 (-43dB), I get a waveform growing downward from 100 and apparently proportional to the input voltage for 0-1.65V, a jump to an waveform that starts at 100, but gets smaller as I further increase the voltage and at about 1.9V it grows downward again (from 100) until at about 3.3V it reaches a maximum (values 103 and -104). This is for the left channel (hooked up to a 5kΩ potentiometer acting as a voltage divider for 5V from a PC power supply) - the right one behaves even more strangely. Maybe it's been left floating (no pun intended)? It would be nice if somebody could explain how the XO-1.5 audio input is wired up exactly. A simplified schematic would be awesome (AIUI Quanta has the IP rights for the schematic, but a simplified version should be fine I think). Sascha (*) X11 OscilloSCOPE. No relationship with the hardware. :) [1] http://xoscope.sourceforge.net/ -- http://sascha.silbe.org/ http://www.infra-silbe.de/ signature.asc Description: PGP signature ___ Devel mailing list Devel@lists.laptop.org http://lists.laptop.org/listinfo/devel
Re: XO-1.5 audio input DC mode
On Wed, Nov 17, 2010 at 1:38 PM, Sascha Silbe sascha-ml-reply-to-201...@silbe.org wrote: Hi! I'm trying to use the XO-1.5 as an oscilloscope, using xoscope (*) [1]. I thought that should be easy to do given that the audio input seems to be specifically designed to do something like this. However my experiences so far are strange at best... For a start there always is a bias voltage. I can reduce its impedance from ~ 15kΩ to ~ 5kΩ and increase it from ~1.75V to ~2.5V, but never turn it off. I also don't understand the values I am seeing: It's always oscillating with half the sampling rate. The Capture level seems to affect both the base line and a partitioning into several value ranges. E.g. for level 39 (-43dB), I get a waveform growing downward from 100 and apparently proportional to the input voltage for 0-1.65V, a jump to an waveform that starts at 100, but gets smaller as I further increase the voltage and at about 1.9V it grows downward again (from 100) until at about 3.3V it reaches a maximum (values 103 and -104). This is for the left channel (hooked up to a 5kΩ potentiometer acting as a voltage divider for 5V from a PC power supply) - the right one behaves even more strangely. Maybe it's been left floating (no pun intended)? It would be nice if somebody could explain how the XO-1.5 audio input is wired up exactly. A simplified schematic would be awesome (AIUI Quanta has the IP rights for the schematic, but a simplified version should be fine I think). Sascha (*) X11 OscilloSCOPE. No relationship with the hardware. :) [1] http://xoscope.sourceforge.net/ -- http://sascha.silbe.org/ http://www.infra-silbe.de/ ___ Devel mailing list Devel@lists.laptop.org http://lists.laptop.org/listinfo/devel With whatever you learn, maybe you can help me sort out the remaining issues with the Sugar Oscilloscpe (Measure) activity (http://activities.sugarlabs.org/en-US/sugar/addon/4197). Meanwhile, this thread may be of interest: http://lists.laptop.org/pipermail/devel/2010-November/030326.html -walter -- Walter Bender Sugar Labs http://www.sugarlabs.org ___ Devel mailing list Devel@lists.laptop.org http://lists.laptop.org/listinfo/devel
Re: XO-1.5 audio input DC mode
As a wild stab at a first guess, it sounds like a software problem to me -- seems like xoscope is not successfully turning off either the bias voltage or the decoupling capacitor (high pass filter). Perhaps a silent failure of some sort? --scott -- ( http://cscott.net/ ) ___ Devel mailing list Devel@lists.laptop.org http://lists.laptop.org/listinfo/devel
Re: XO-1.5 audio input DC mode
On Wed, Nov 17, 2010 at 2:46 PM, C. Scott Ananian csc...@laptop.org wrote: As a wild stab at a first guess, it sounds like a software problem to me -- seems like xoscope is not successfully turning off either the bias voltage or the decoupling capacitor (high pass filter). Perhaps a silent failure of some sort? If you've got access to a signal generator (or another machine with a sound card), feeding in a 1kHz square wave with an offset (say 0 off, 1V on) is probably a better diagnostic than using your potentiometer. If my wild guess is correct, then you should see a characteristically rounded square wave with no offset. Then you could poke at the software until (a) the rounding goes away, and (b) you see the offset you expect, which would indicate that the decoupling capacitor has successfully been switched out of the circuit. --scott -- ( http://cscott.net/ ) ___ Devel mailing list Devel@lists.laptop.org http://lists.laptop.org/listinfo/devel
Re: XO-1.5 audio input DC mode
Sascha This matches what Walter and I are observing with TurtleArt 103. TA uses commands issued to amixer, amixer seems to be behaving inconsistently. Biases of 5k and 15k have been observed but unpredictably. The amixer commands that should switch the bias off just change the gain. With 0dB gain, bias off commands, the output is +26000 0V, 0, 1.7V, -26000 3.4V. Try to switch off the bias and the gain changes to +-14000. I am using the tip of a stereo plug which I thought was the right channel? Tony Hi! I'm trying to use the XO-1.5 as an oscilloscope, using xoscope (*) [1]. I thought that should be easy to do given that the audio input seems to be specifically designed to do something like this. However my experiences so far are strange at best... For a start there always is a bias voltage. I can reduce its impedance from ~ 15kΩ to ~ 5kΩ and increase it from ~1.75V to ~2.5V, but never turn it off. I also don't understand the values I am seeing: It's always oscillating with half the sampling rate. The Capture level seems to affect both the base line and a partitioning into several value ranges. E.g. for level 39 (-43dB), I get a waveform growing downward from 100 and apparently proportional to the input voltage for 0-1.65V, a jump to an waveform that starts at 100, but gets smaller as I further increase the voltage and at about 1.9V it grows downward again (from 100) until at about 3.3V it reaches a maximum (values 103 and -104). This is for the left channel (hooked up to a 5kΩ potentiometer acting as a voltage divider for 5V from a PC power supply) - the right one behaves even more strangely. Maybe it's been left floating (no pun intended)? It would be nice if somebody could explain how the XO-1.5 audio input is wired up exactly. A simplified schematic would be awesome (AIUI Quanta has the IP rights for the schematic, but a simplified version should be fine I think). Sascha (*) X11 OscilloSCOPE. No relationship with the hardware. :) [1] http://xoscope.sourceforge.net/ -- http://sascha.silbe.org/ http://www.infra-silbe.de/ ___ Devel mailing list Devel@lists.laptop.org http://lists.laptop.org/listinfo/devel _ This mail has been virus scanned by Australia On Line see http://www.australiaonline.net.au/mailscanning ___ Devel mailing list Devel@lists.laptop.org http://lists.laptop.org/listinfo/devel
