From: Paul Hannah <[email protected]> Reply-To: "[email protected]" <[email protected]> Date: Tuesday, December 16, 2014 at 10:26 PM To: "[email protected]" <[email protected]> Subject: Re: [beagleboard] Sensing flowmeter / protecting analog input
> John, > > Cheers, it's a Gicar 9.0.95.05g -- sits in a cafe-style coffee machine, though > this'll only be the first install and the others may be different (but > presumably similar) parts. OK, I couldn¹t find a data sheet, but I think this is a three pin device, GND, POWER (4.5 - 20V) and PULSE. If this is correct, then all you need is a resistor divider as you suggested and a schmitt trigger to clean up the signal and then feed this directly into one of the GPIO pins. The schmitt trigger should be powered from VDD_3V3B and enabled with SYS_RESETn. Regards, John > > On Wed Dec 17 2014 at 17:02:30 John Syn <[email protected]> wrote: >> >> 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/bo >>>>> ok >>>>> <http://www.packtpub.com/building-a-home-security-system-with-beaglebone/b >>>>> ook> >>>>> >>>>> >>>>> 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. >> 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.
