From: Paul Hannah <[email protected]> Reply-To: "[email protected]" <[email protected]> Date: Tuesday, December 16, 2014 at 9:27 PM To: "[email protected]" <[email protected]> Subject: Re: [beagleboard] Sensing flowmeter / protecting analog input
> 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. BTW, what is the flowmeter part number. Perhaps there is a much simpler way to interface this to the BBB. Regards, John > > 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 won¹t work. Look at fig 4 in >> this document for the zener voltage characteristics DDZ9678: >> >> http://www.diodes.com/datasheets/ds30410.pdf >> <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 >>> <http://www.packtpub.com/building-a-home-security-system-with-beaglebone/boo >>> k> >>> >>> >>> From: [email protected] [mailto:[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] >>> <mailto:[email protected]> . >>> For more options, visit https://groups.google.com/d/optout >>> <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] >>> <mailto:[email protected]> . >>> For more options, visit https://groups.google.com/d/optout >>> <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 >> <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. 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