Amazing already explained in previous post sounds like original poster has no knowledge that modern processor are powered at 3.3 volts or less and never bothered to read schematics. I applaud the willingness to walk through the examples
Sent from Yahoo Mail on Android On Sat, Dec 17, 2016 at 6:45 PM, Dennis Lee Bieber<[email protected]> wrote: On Sat, 17 Dec 2016 15:29:07 -0800 (PST), Chris Fink <[email protected]> declaimed the following: >Thanks for the replies, everybody. I am confused about the voltage >requirements of the BBB...it accepts a 5V power supply (in the slot next to >the ethernet cable input), and yet it is a 3.3V device? In addition, the >demo prescribes that the PIR be powered by pin P9_5, which is a 5V supply. >So if you could further explain how/why the BBB is a 3.3V device, I would >appreciate it. > The first chip (U2 I believe) near the 5V power connector is a voltage regulator which drops the voltage to 3.3V to power all the rest of the chips. The 5V is passed through to the connectors. Signal pins to the main processor are only safe with 3.3V (and the analog inputs are even more critical -- they only handle 1.8V)... Open collector devices (those that /need/ a pull-up resistor) are designed such that they do not "push" a voltage to the line, they only drive the line down to ground. When not pulling down to ground the line floats -- the pull-up resistor is what lifts the line to a stable "high", so a pull-up to 3.3V would be valid. Even if the device is using a 5V power supply, it doesn't push 5V out the signal line. USB is also 5V (and possibly up to 500mA IF the source is not split via a hub to multiple devices [this is USB 2.0; 3.0 has different capabilities]. >demo, it continually oscillated between detecting motion and not detecting >motion--even though there was nothing moving in front of it! The LED light >turned on and off pretty regularly, with a period of about 5 seconds. >Perhaps this is somehow due to the PIR not being supplied the full 5V? > Sounds almost like an RC timer circuit... Again, if yours has that retrigger jumper, how does it behave in the other position? -- Wulfraed Dennis Lee Bieber AF6VN [email protected] HTTP://wlfraed.home.netcom.com/ -- For more options, visit http://beagleboard.org/discuss --- You received this message because you are subscribed to the Google Groups "BeagleBoard" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To view this discussion on the web visit https://groups.google.com/d/msgid/beagleboard/05mb5cpk2lrfpakujb3dbjkfjgq2cuvle2%404ax.com. For more options, visit https://groups.google.com/d/optout. -- For more options, visit http://beagleboard.org/discuss --- You received this message because you are subscribed to the Google Groups "BeagleBoard" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To view this discussion on the web visit https://groups.google.com/d/msgid/beagleboard/848790812.7360649.1482033511296%40mail.yahoo.com. For more options, visit https://groups.google.com/d/optout.
