A resistor divider is not going to protect the BBB. if you want true protection you will need to feed the BBB ADC from a 1.8v op amp that way the BBB input cannot go over the rails of the op amp. OR see attached jpg for another method A zener doide will also not be 100% protective as the zener may not be fast enough to react to a high voltage
On 10/30/2015 9:00 AM, Przemek Klosowski wrote: > You can't feed more than 1.8V to ADC without damaging it. You can, > however, scale it with a simple resistor divider (resistor R1 > connected between the ground and second resistor R2, which is then > connected to your signal), and hook the ADC to the middle of the > divider where it will be scaled down by the ratio R1/(R1+R2). How > quickly do you want the result? If it's miliseconds, Linux is > perfectly capable of that; if microseconds, then PRUs can do it; > otherwise, you'd have to come with an analog multiplier circuit. > > On Fri, Oct 30, 2015 at 7:23 AM, John <[email protected] > <mailto:[email protected]>> wrote: > > > I'm a hobbyist with a recent BBB and I want to use a couple of ADC > channels in real time (alternate). As nearly as I can tell, this > is not supported by the two risk units. > Have I missed something? > > BBB and Linux are new to me. One of the things I would like to do > is compute a ratio between two voltages, each of which might > exceed 1.8 VDC. One solution might be to use DACs to sent > feedback voltages to operational amplifiers that are supplied by > 1.8 VDC. The goal is to determine the ratio as quickly as > possible and without waiting for Linux to get around to it > (waiting for the ADC to happen). > > John > > > > > -- > 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] > <mailto:beagleboard%[email protected]>. > 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] > <mailto:[email protected]>. > 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]. For more options, visit https://groups.google.com/d/optout.
