Can you post a HD photo of the bottom side of that relay module?
If you're up to the task can you assemble the circuit I posted on a perf board and integrate into the relay module?

 

View attachment 287773Try this arrangement.
When the tank is full both sensor outputs are low and so is the output from the 555. When the water level drops below the bottom sensor both sensor outputs will be high triggering the 555 output high.
D1 and R1 form a latch function to keep the output on the 555 high as the water level rises and the bottom sensor goes low again.
When the water level rises to the top sensor the low output will reset the 555.

Will try that, thank you.
In this case it will be probably easier to get the IC and build it from scratch then rework the old controller.
In this configuration it should work with my sensors direct?

 

Can you post a HD photo of the bottom side of that relay module?
If you're up to the task can you assemble the circuit I posted on a perf board and integrate into the relay module?

No components on the back side
Yes, that would be easier for sure then rework the board. I will have to order the components.

 

Will try that
In this configuration it should work with my sensors direct?

It should. What is the supply voltage for the sensors?

 

It should. What is the supply voltage for the sensors?

5V, same as the controller.
Found desoldered 555 in my scrap pile, will try it out now.
The design is so simple it's almost unbelievable

 

What relay will you be using?
May need a transistor also.

 

What relay will you be using?
May need a transistor also.

mini relay 5V/35mA
Got it all set, should I power it on without the transistor?

 

35 ma is fine, should not need transistor.

 

35 ma is fine

Hm, no go, nothing happening, will test some voltages to see what's going on.
Instead of 4.7k resistor I used 2x 2.2K in series, is this crucial?

 

Hm, no go, nothing happening, will test some voltages to see what's going on.
Instead of 4.7k resistor I used 2x 2.2K in series, is this crucial?

No

 

With no sensors connected the relay should activate immediately.

 

With no sensors connected the relay should activate immediately.

It doesn't, also there is steady 0V on those sensor inputs.

 

The sensors must have internal pullup resistors, but the relay should have activated with out the sensors connected. Are you sure the 555 is good?

 

The sensors must have internal pullup resistors, but the relay should have activated with out the sensors connected. Are you sure the 555 is good?

Don't know if it's good or not, will order couple new.
Postec pic of my nasty wiring above
only positive voltage is 3.5V on pin5 and power on 8
0V on the relay

 

I'll update the schematic here shortly.

 

I'll update the schematic here shortly.

Thank you!

 

If you just need to reverse the sense of the output of the sensor then this can be done with a single transistor and resistor. as below.


Les.

 

If you just need to reverse the sense of the output of the sensor then this can be done with a single transistor and resistor. as below.
View attachment 287776

Les.

Thank you, will try that tonight.
I did this before but I used 10K resistor and it did not work for me.

 

Re post #38. It should work just as well with a 10K pull up resistor. Did you measure how low the output of the sensor went ?
The sensor may have an internal pull up resistor that did not allow it's output to go low enough to turn off the added transistor.

Les.

 

Updated schematic if sensor has pullup resistor.

Without pullup resistors. Looking at the image in post #2, don't see a pullup resistor.