I've had a bit of a dig on element14, this seems to fit the bill ( http://au.element14.com/texas-instruments/sn74lvc1g14dbvr/ic-schmitt-trigger-inverter-smd/dp/1470878) but it's not suitable for a breadboard prototype. You don't know where I should be looking for a suitable prototyping product by any chance?
Thanks, Paul. On Wed Dec 17 2014 at 17:58:21 John Syn <[email protected]> wrote: > From: Paul Hannah <[email protected]> > Reply-To: "[email protected]" <[email protected]> > Date: Tuesday, December 16, 2014 at 10:50 PM > > To: "[email protected]" <[email protected]> > Subject: Re: [beagleboard] Sensing flowmeter / protecting analog input > > Yes, that sounds exactly like the device. > > Awesome, didn't even know such a beast existed. Will do my reading tonight. > > http://www.ti.com/lit/an/scea046/scea046.pdf > > Page 4 explains the concept. > > Regards, > John > > > > Thanks again, > Paul. > > On Wed Dec 17 2014 at 17:47:20 John Syn <[email protected]> wrote: > >> 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 couldn't 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 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:beagleboard@ >>>> googlegroups.com <[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. >>> >>> -- >>> 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. > > -- > 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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