From: William Pretty Security <[email protected]> Reply-To: "[email protected]" <[email protected]> Date: Tuesday, December 16, 2014 at 7:00 PM To: "[email protected]" <[email protected]> Subject: RE: [beagleboard] Sensing flowmeter / protecting analog input
> Hmm > > Maybe a 1.8v zener ? I see this recommendation all the time, but it won¹t work. Look at fig 4 in this document for the zener voltage characteristics DDZ9678: http://www.diodes.com/datasheets/ds30410.pdf You will see that the zener voltage is at 1.8v when the current is at 80uA, but at 100uA, the voltage exceeds the maximum allowed on the ADC input. The only way to deal with this situation is to use a proper signal conditioner. First start with the voltage range of the input and then scale that down with an op-amp. You can also offset the reference to deal with negative voltage inputs. To the OP, you are only using this for counting, why use ADC. Why not scale/condition the output of the hall-effect flowmeter and use a digital input? Regards, John > Or 1N4007¹s in series = 1.4V > > "No one could make a greater mistake than he who did nothing because he could > do only a little." > "All that is necessary for the triumph of evil is that good men do nothing" > Edmond Burke (1729 - 1797) > http://www.packtpub.com/building-a-home-security-system-with-beaglebone/book > > > From: [email protected] [mailto:[email protected]] On > Behalf Of Paul Hannah > Sent: Tuesday, December 16, 2014 9:09 PM > To: [email protected] > Subject: [beagleboard] Sensing flowmeter / protecting analog input > > Hi, > > > > I'm looking to build a system to sense 'steps' of a hall-effect flowmeter. > > > > My first throught is to use a voltage divider and rectifier circuit to get > down to the 0-1.8v I need. > > > > The problem I have is that every install may potentially have a different > input voltage. > > > > I'm wondering if there's a simpler way to do this. I really only need to clip > the voltage between 0-1.8v, it doesn't matter if it spends 90% of it's time > clipped and throws away the negative half of the signal completely as I'm only > interested in a count. > > > > The current draw will be in the millivolt-range used by the adc input, so it > shouldn't need anything too heavy. > > > > My first thought is a simple voltage regulator set to 1.8v, but I don't know > enough about them to know whether it's a viable option or which to choose. > > > > Any suggestions? > -- > 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. > > > No virus found in this message. > Checked by AVG - www.avg.com <http://www.avg.com> > Version: 2015.0.5577 / Virus Database: 4253/8748 - Release Date: 12/16/14 > > > No virus found in this message. > Checked by AVG - www.avg.com <http://www.avg.com> > Version: 2015.0.5577 / Virus Database: 4235/8735 - Release Date: 12/14/14 > -- > 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.
