On 1/19/15, 9:41 PM, "maxmike" <[email protected]> wrote:
>On Monday, January 19, 2015 at 6:23:49 PM UTC-8, john3909 wrote: >> From: maxmike <[email protected]> >> Reply-To: "[email protected]" <[email protected]> >> Date: Monday, January 19, 2015 at 5:10 PM >> To: "[email protected]" <[email protected]> >> Subject: [beagleboard] Same wire going to adc and comparator kills >>interrupts >> >> >> >> I have the output of an op amp go directly to the BBB adc and the >>values are read correctly. >> But, the same wire is going to a comparator to generate interrupts. >> It looks like the comparator is not firing all the way to ground >>because of the adc drag. >> I thought of placing a 1K resistor from the adc input to ground but >>that does nothing. >> Anything higher is going to bother the adc. I'm stumped. >> Well, it depends on the opamp. Some opamps are not able to drive all >>the way to 0V, but as long as it goes below the logic low for your I/O >>input, it shouldn¹t matter. If you really want an opamp that goes to >>zero, choose one that is capable to operating rail to rail. Also, the >>opamp feedback circuit is important because you are going to want some >>hysteresis or your GPIO input might see some noise close to the trigger >>point. >> >> >> Regards, >> 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]. >> >> For more options, visit https://groups.google.com/d/optout. > >The lmv762 comparatorworks 100% if I sever its input from the adc - it's >only when the adc is tied to it that it does't go to ground at the output. Well, the datasheet shows VO has a worse case voltage range from 250mv to VCC-0.35v. Is this consistent with your measurements? Regards, 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]. >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.
