my water meter needs a better voltage divider

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hi James,
The wiper of the potentiometer is assumed to be adjustable from 0 to 100% of the pots value, so .49 means the pot has been adjusted to 49% of its value.
 
Ok. CA3240 and the LM339A (which I think is quad) should be what I need.

For the caps, just regular ceramic? I always never know which type cap to use in what situations?

So, I should be able to just the two pots to control the "high" and "low" thresholds for the pulse output?

thanks,

-jr
 
hi James.
Confirm your input voltages and range and I will re run the sim with your values.
 
KISS -- I like that idea! I'm all for using a single chip where possible.

Eric - thanks! My input values are basically 1.99V to 2.19V or about 200mv amplitude. It's similar to the original posters values. The values will really depend on how it is positioned on the water meter. So I need some flexibility in tuning it. That is what the LED is for. I'm thinking as designed with wipers @ 50% I should have enough to play with.

thanks,

-jr
 
KISS --

So, if I understand the data sheet correctly on the chip you mention, it adapts to the peak of the pulse? So nothing else I really need to do with it? Will this work with 5V logic? Seems like it says it will, but the typical Vcc is 10V? any other chips I might consider?

-jr
 
KeepItSimpleStupid said:
Why don't you use one of these: Variable Reluctance Sensor: https://www.electro-tech-online.com/custompdfs/2012/04/snosbu8e-1.pdf
Click to expand...


So, I've read this data sheet and it seems like it would be perfect for my application..

My question is what my signal is ~ 2V with a 200mv sinusodial pulse. So, it ranges from 1.99v to 2.19v. So, it technically never crosses zero? Wouldn't you need to come up with a circuit which will re-base this right at zero so that it would go -10mV and +10mV?

thanks!

-jr
 
Eric --

were you able to re-run the sim withe 1.99 to 2.19v? Hopefully we can achieve that with just some value changes on the pots?

thanks,

-jr
 
Jamesr219 said:
Eric --

were you able to re-run the sim withe 1.99 to 2.19v? Hopefully we can achieve that with just some value changes on the pots?

thanks,

-jr
Click to expand...

hi James,
This is a rerun with your signal, I have removed the pre filter in order to speed up the simulation.

Note the new values in series with the two pots
 
ericgibbs said:
hi James,
This is a rerun with your signal, I have removed the pre filter in order to speed up the simulation.

Note the new values in series with the two pots
Click to expand...

Eric -- thank you so much for re-running this. The values will really depend on the sensor placement. They may be +/- 50mV or so. Looks like I should have plenty of flexibility with the 10k pots in there. I plan to do the filter on the front end to make it as robust as possible.

- For all the caps, should I just use ceramic caps or different type? I never know which type of use in which situations.
- R10 is that 3.3k or 3k or 33k?

Thanks again. So glad I found this forum.
-jr
 

hi,
The 220uF [ or a 470uF] will be electrolytic, say 16V or 25V working voltage.

You could use ceramic for C2,3 and 4, make them all 470nF

E.
 
Thanks Eric. I will use C2 as 220uF (or 470uF) and then C1, C3, C4 as 470nF ceramic. (I think you typo'd C2 saying 470nF..).

What about label on R10? it indicates 3k3?

Edit -- Also, what about C5, C6 for the filter? Putting together digikey order for these parts.

-jr
 
Last edited:

hi,
3k3 aka 3.3k aka 3300R... in Euro Techno speak the K replaces the 'decimal point'

E
 
ahh.. That is kind of what I thought. 3.3k Got it.

For the caps in the filter section -- C4, C5? are those ceramic or electrolytic?

What is impact on tweaking some of these resistor values to common values? Really just the 1.62k will be 1.6k and 19.1k will likely go to 18k or 20k. I assume that these are all close to the 5% tolerance so it will be fine?

Thanks,

-jr
 
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