The published XO-1.5 spec is very conservative. But unfortunately, layout concerns prevented me from providing too much protection. The parts used (1/16W) should protect up to 9V continuously, and up to higher voltages for shorter periods of time. With excessive voltage, the protective resistor should blow out isolating the over-voltage diodes and codec from the input jack and preventing hard-to-repair damage.
Regards, wad On Nov 15, 2010, at 3:33 PM, Ed McNierney wrote: > From the XO-1.5 hardware spec at > http://wiki.laptop.org/images/f/f0/CL1B_Hdwe_Design_Spec.pdf > > "2.7.4 External Microphone Input > > A stereo jack is provided on the laptop for connecting an external > microphone, switch, or other sensor. This jack is connected to the audio > codec’s microphone input, with provides a programmable gain preamplifier, > with a gain of 0, 10, 20, or 30 dB. The input impedance is 10 KΩ. > > A DC blocking capacitor may be inserted into the input signal path, under > software control. This is used when the input is an audio signal. When used, > the frequency response of the input is flat down to 10 Hz. > > A bias voltage (1.5 or 2.5V, with a 3 KΩ source impedance) may also be driven > onto this external microphone input, under software control > > This may be used to power external electret condenser microphones, or used to > sense whether an external switch is open or closed. Due to the high impedance > of the bias source, this input may safely be shorted to ground. > > An external voltage applied to this input is limited to between 0 and 3.5 V. > Inputs exceeding this range may cause excessive current to flow through a > protective diode. > > When the external microphone jack is in use, the internal microphone is > disconnected, and the indicator light indicating microphone use is disabled. > The state of this jack may be queried by software." > > - Ed > > On Nov 15, 2010, at 3:28 PM, fors...@ozonline.com.au wrote: > >>> >>> This was done starting with the XO-1.5, and will also be >>> done on the 1.75. >> thanks >> what is the allowable input voltage, i dont think its on the wiki? >> _______________________________________________ >> 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
