John, Digital input, hadn't thought of that but it makes sense, but I'm even less sure of myself in that arena...
I have to admit first my electronics knowledge is very rusty... Maybe I can use a voltage divider after the diode/s to halve that 1.8v+ down to a safe 1.0v-ish. My first thought here is to use a zener diode as in here http://www.electronics-tutorials.ws/diode/diode42.gif) with a voltage divider after. Is the reverse voltage low enough to be safe with the BBB? If not, what if I set up something like this, but make D_Z1 a normal diode so that the reverse current is completely stopped? Again, not interested at all in the quality of the signal as long as I can determine the number of cycles. Sorry for the electronics 101 questions, appreciate all your time. Cheers, Paul. On Wed Dec 17 2014 at 14:55:09 John Syn <[email protected]> wrote: > > 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 won't 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 1N4007's 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] > <[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 > 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 > 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. > -- 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.
