this is a design for a water level probe that i have now on my work bench and try to get some improved working

it was pretty sensitive (relais chattering) before i put the capasitors in but i am afraid that if i make the probe cables longer they still pick up noise and don't work properly

is shielded cable a solution??

or is there another solution?

please advice

Thanks
Robert-Jan

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TMP1.JPG (199.7 KB, 38 views)

 

hi Robert-Jan

A simple resistor/capacitor filter on the inputs from the rods, would remove most low levels noise

__________________
Eric
"Good enough is Perfect"

PIC tutorials:
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Bill's: www.blueroomelectronics.com/

 

anny sugestions about the value

the resistance of the water between the propes is measured over the farest probe litle under the 2 M ohm would that be suficient if i would put a normal capacitor on 10 n between the probe and comon probe???

Robert-Jan

 

Try moving the relays into the collector leads.
Mike.

 

hi,
Use good quality low leakage capacitors, so as not to load the 10M0.

Is that 40106 OK.? with the 47uFs directly on the output pins.

I would also follow Mike's suggestion regarding the relays in collector.

__________________
Eric
"Good enough is Perfect"

PIC tutorials:
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Bill's: www.blueroomelectronics.com/

 

the relais are already changed from position the capacitors is wat i have laying around and localy bought (that means ???? for the quality thing)

will experiment a bit more

Thanks for the sugestions

Robert-Jan

 

Hi,
Quality, I mean capacitors that have a low leakage current.

__________________
Eric
"Good enough is Perfect"

PIC tutorials:
Gramo's: www.digital-diy.net/
Bill's: www.blueroomelectronics.com/

 

probably i have the good one than because the circuit is working perfecly now

put between the probes end the comon probe 47 n Farat

did change the location of the relais and i could remove the 47 uF it works as good without as with them

Thanks

jump now to another part of my project

Robert-Jan

 

Hi,
Another problem area, is mains 'hum' pick up on the high impedance CMOS inputs which are tied to +V via a 10M0.

__________________
Eric
"Good enough is Perfect"

PIC tutorials:
Gramo's: www.digital-diy.net/
Bill's: www.blueroomelectronics.com/

 

The inputs need 1M series resistors to help prevent destruction of the IC from static electricity.

__________________
Uncle $crooge

 

Thanks for all the sugestions
as shown in the shematic this is as i have build it now and it seems to work fine on my work bench

put the extra inverters in to the circuit to get a better efficiency as the purpose is that the Water tank should be full so that means the relais are now in the new schematic only activated when the level drops

for a sump it would be other way around

still another question
about the hum in the suply (as eric mentioned)

the suply comes from the 7812 and accompanied with the usual capacitors
is it still advisable to use shielded cable??

its my intention to put the the whole circuitry as close to the probes as posible (3 meters Max) and that only the relais switch contacs will be wired to the main control panel so that is already a different circuit

Robert-Jan

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TMP5.JPG (173.3 KB, 11 views)

 

a water level meter w/ leds, no noisy relays
http://www.electronic-circuits-diagr...armsckt6.shtml
fewer parts to say the least

 

hi Robert-Jan

I would recommend adding decoupling capacitors on the supply rails.
Also increase the base current into the relay transistors.

Added the 40106 inversion 'circles'

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untitled.jpg (59.0 KB, 7 views)

__________________
Eric
"Good enough is Perfect"

PIC tutorials:
Gramo's: www.digital-diy.net/
Bill's: www.blueroomelectronics.com/

 

that's nice for indication but i have to switch the control contactors that switch the pumps so relais would be the best/economical solution

the relais are the small print relais and they are located in a pump room so there is no way you will notice the sound of the relay withe all the sounds that the pumps are making

Eric thanks again for your advise, consider it done

the decoupling capacitor (100nF) i always put next to any Cmos IC but often forget to draw it in a schematic during the "designing phase" and put it in the drawing when everything is finished

Robert-Jan

 

instead of the leds use 5v relays or triac opticouplers might be better.
the use of the opticouplers would isolate the 110 from the rest of the circuit in a safe manner..
MOC2023 come to mind.