Tank level sensor - trigger switched outputs - thoughts?

[sailorbenji]

Hi all,

Something I've been meaning to do for the longest time is fit float switches to our forward water tank, for our water maker. This would allow us to leave it on maintenance mode, where it would use water to flush itself through, and then refill the tank.

The items provided to do this are two physical float switches that I would need to fit to the side of the tank, top and bottom. Access to the tank is a nightmare, in fact I can't see how I could drill the appropriate holes without dismantling most of the saloon, and this got me wondering......

With cheap boards like Arduinos and Pis being so prevalent, would it be feasible for such a device to read the resistance level from our existing analogue level gauge, then for it to create voltage free switch contacts when it detects the resistance levels are at full and empty?

I know there are a few amateur electronics gurus around these parts, and keen to get thoughts before I embark on the path further (I'm far from a programmer!).

Thanks, Ben

 

[Moodysailor]

Yes, this is possible. You only need to tell the program at what value to turn on.

Actually doing it is outside of my knowledge base, but there a bunch of people on here (and i'm sure on YouTube) who know ?

Edit to add - if it's a European sender the values are 0 ohm when empty and 190 ohm when full. I advise measuring the actual resistance value on your sender when empty and full as there can be dead spots or air gaps that prevent full range readings, then apply a margin or error (+/- 3% or so) in the programming

 

[andsarkit]

Resistance isn't measured directly. You need to pass a known current through it and measure the voltage drop or apply a known voltage and measure the current. An add on system will have to tap into this with a high impedance so it does not alter the existing readings. It is all perfectly possible and the easiest way might be a voltage controlled relay such as this 6~80V Voltage Detection Charging Discharge Monitor Relay Switch Controller U7X4 | eBay . First you need to get a multimeter and see what sort of voltages you get on your existing meter for full and empty.

 

[vas]

main problem would be to keep the existing analogue gauge showing water level AND use the same sender via an arduino / raspberry to get the level of the water tank...

 

[sailorbenji]

main problem would be to keep the existing analogue gauge showing water level AND use the same sender via an arduino / raspberry to get the level of the water tank...

Any clue how to avoid affecting the original analogue gauge?

 

[DavidTocher]

Most level gauges use a fixed supply voltage feeding the display/meter via the variable resistance of the sender. The voltage at the junction of the sensor and meter is what needs to be read. An arduino can measure this voltage and because it has a very high impedance it won't affect the display. The problem is that the max voltage an arduino analog pin will accept is 5 volts but the usual supply on a boat is a nominal 12 volts. A simple voltage divider can solve that problem but other, better, solutions are possible. Once the arduino has read the sensor then you are home and dry.

 

[andsarkit]

Any clue how to avoid affecting the original analogue gauge?

If the sender is 190 ohms then putting a resistance 100 times greater across it will only alter the reading by 1%. Most electronics will have an input impedance of greater than 1M ohm so will not affect the reading.

 

[William_H]

As said it is unlikely any voltage detecting device will affect the existing reading. Simplest solution for those electronically minded is to set up one or 2 voltage comparators.
This is a simple Op amp device which has a set reference voltage on one input (from a zener diode) and the voltage to be sensed fed tot he other input via an adjustable resistor.
When the sensed voltage exceeds the reference voltage it changes output from near battery voltage to zero. This can drive a relay (perhaps via a power transistor) . Set up any number of these comparators to get operation at any voltage.
Or as shown above Ebay have all sorts of relay boards set up to activate at a specific adjustable voltage. (using copmparators) ol'will

 

[Alex_Blackwood]

Hi all,

Something I've been meaning to do for the longest time is fit float switches to our forward water tank, for our water maker. This would allow us to leave it on maintenance mode, where it would use water to flush itself through, and then refill the tank.

The items provided to do this are two physical float switches that I would need to fit to the side of the tank, top and bottom. Access to the tank is a nightmare, in fact I can't see how I could drill the appropriate holes without dismantling most of the saloon, and this got me wondering......

With cheap boards like Arduinos and Pis being so prevalent, would it be feasible for such a device to read the resistance level from our existing analogue level gauge, then for it to create voltage free switch contacts when it detects the resistance levels are at full and empty?

I know there are a few amateur electronics gurus around these parts, and keen to get thoughts before I embark on the path further (I'm far from a programmer!).

Thanks, Ben

Can you not fit a vertical switch from the tank top? Do GOOGLE search for "Vertical Float switch" RS have one from about £35. Saves messing about with home made electronics!