old solar heater controller

[johnny78]

hi Guys
i was asked to fix this device for some friends but i couldnt understand how it works of find any information about it
the MCU is P87LPC764FN which i downloaded the datasheet & there is no analog input
the sensor reads the water level 4 steps & the temp of water using 4 wires & im not familiar with this kind of connection
the four wires enters 74hc04 hex inverter which i will draw the input schematic
the sensor has 4 wires which i cant find what is it for

https://www.aliexpress.com/i/1005001734767504.html
here is the controller

any help will be great
Johnny

--- Updated Sep 3, 2024 ---

hi Guys
i was asked to fix this device for some friends but i couldnt understand how it works of find any information about it
the MCU is P87LPC764FN which i downloaded the datasheet & there is no analog input
the sensor reads the water level 4 steps & the temp of water using 4 wires & im not familiar with this kind of connection
the four wires enters 74hc04 hex inverter which i will draw the input schematic
the sensor has 4 wires which i cant find what is it for

https://www.aliexpress.com/i/1005001734767504.html
here is the controller

any help will be great
Johnny

here is the sensor
https://www.aliexpress.com/item/1005003752897979.html

 

[barry]

Hi,


No.

Your "variable resistor" is marked with "VR", which means "voltage dependent resistor" and is the overvoltage protection to the sensor input at the PCB.
And these VRx devices have nothing to do with the function at all, it is just protection. You may ignore them. These are the blue disks in the picture.

I guess you misinterpreted the VRs (protection devices) as the sensor.
But the sensor is off PCB (thus not drawn into the schematic) ... connected with wires.

So it is:
R2 goes from the output of U1D ... through the blue wire to the sensor, and back via the red wire to the PCB as input to R1 - R2 to U1D_input.


As the OP wrote in post#1:

Since the sensor is "wired" it is not "on PCB" thus not drawn into the PCB schematic.
But the wire connector (pad) is drawn ... and marked with the wire colors.

Klaus

I guess i didn’t make the leap to assuming the sensor is a resistor connected between the two terminals. nothing presented here would indictate that, as opposed to it being a capacitive sensor, or anything else.

 

[KlausST]

Hi,

2 wires are 10k NTC

this - to me - sounds like a resistive temperature sensor.

Klaus