Argghhhhh.....left out the one megohm feeding the sender which becomes part
of its network.

So B+-----1MΩ------sender wire+top bolt---/\/\/\/(black box)----next
bolt----/\/\/\/---third bolt----/\/\/\/----B-

Yrs,
d

On Mon, Sep 3, 2018 at 8:44 PM, David Beierl <dbeierl@attglobal.net> wrote:

> I've been playing with arduino off and on for a while and this seems like
>> an application for that.  it could probably be configured to read the
>> water
>> contacts such that there would be more leeway as far as all the
>> connections
>> being perfect and variations in water source.
>
>
> The resistor network that the panel compares against is:
>
> B+ --------150K---100K---R---100K---Y---100k---G---150K--------- B-
>
> That makes the green light at 25% of B+ or less, yellow from 25-42%, red
> from 42-58%, and no LED above 58%.**
>
> The network for the sender is similar:
>
> B+ is fed through one megohm to the green sender wire at the top bolt, and
> the bottom bolt is grounded.
>
> So B+-----sender wire+top bolt---/\/\/\/(black box)----next
> bolt----/\/\/\/---third bolt----/\/\/\/----B-
>
> As the water rises it first touches only the ground bolt, for no LED.
> Then it successively shorts the bottom bolt for red, middle for yellow, and
> top for green through the water to the ground bolt.  I don't have a magic
> box to measure the values, but they have to be such that the resulting
> voltage divider with the tank water in parallel with the bottom n segments
> will cause the output voltage to be between the thresholds.
>
> Since both networks are connected to B+ the absolute voltage doesn't
> matter -- it's the proportion that counts.
>
> The voltage lights behave similarly except they compare against a network
> fed by a 5.1v zener diode.
>
>   And then you could also set
>> the voltage level lights to switch at specific voltages.
>
>
> You need proportions rather than absolute voltages unless you supply a
> regulated voltage to the sender.
>
> The existing board is simple and works well, sometimes with a tweak
> resistor added to the comparison network.
>
> The later float wand of course gets rid of the uncertainty of water
> resistance at the expense of mechanical fragility/leak susceptibility and
> losing the lowest (no LED) level indication.**
>
>
> **Note that the '80-81 panels with four water LEDs G Y R R and no flame
> detector will light the bottom red in this case, rather than showing no
> LED.   They will also shut off the water pump at that time.
>
> Yrs,
> d
>