Folks, I've just had a discussion with my colleague, and we realized that the reason that I'm trying to connect all the grounds together, is because the 5V and 12V power 2`1335467i['\ are not co-grounded, and I'm forcing them to have the same ground level to transfer the signal (I've measured the voltage difference between the two grounds, and it's at least 300mV! And it's not stable), so that there might be a large current (aka ground loop) through the BB because of the ground difference between the two power sources, since the ground of them are 'floating'. If I use a single power source with double outputs, like this <http://www.digikey.com/product-detail/en/VGD-30-D512/102-2527-ND/2941852?WT.mc_id=IQ_7595_G_pla2941852&wt.srch=1&wt.medium=cpc&WT.srch=1>, maybe I can literally eliminate the red line on the schematic, and still have the same ground through all the boards.
How does this sound? Maybe this is the ultimate solution! Henry On Thursday, October 29, 2015 at 8:36:30 PM UTC-4, Dennis Lee Bieber wrote: > > On Thu, 29 Oct 2015 09:49:39 -0400, Yongfan Men > <[email protected] <javascript:>> declaimed the following: > > >This DAC has a flexable input voltage option. So if I'm inputing a 3.3V > >voltage to it, by controlling via I2C, I can get a 0~3.3V linear voltage > >output. That 5V power source is just for powering the relay and the BBB & > >touch screen. So I don't think I'm driving a 5V circuit with BBB. On the > >other hand, I think the BBB can also output 5V, so I can as well give the > >DAC a 5V directly from BBB, right? > > > NO... The BBB only handles 3.3V digital (and the analog input is > only > 1.8V as I recall). > > You should be using a level shifter between the BBB 3.3V and the > 5V > target chip. > > You should probably also be using some sort of block for back-EMF > on > the relay (when you shut off the coil, the dropping voltage will feed back > out on the control leads). > -- > Wulfraed Dennis Lee Bieber AF6VN > [email protected] <javascript:> 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]. For more options, visit https://groups.google.com/d/optout.
