old solar heater controller

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johnny78

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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 ---

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

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barry said:
Maybe it's a serial device? No way to tell from a crappy Ali express picture and nothing more.
Click to expand...
yes i know but this i the only informations i got
I WAS WONDERING IF ANYONE KNOWS ANYTHING ABOUT IT

here is more information i have now
this is the input section of the 4 wires sensor

& here is a screenshot of the inputs description in the datasheet

 
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What heats the water? Painting the tank a dark color and mounting it in the sun? (Or unused power from hydro or wind generator?) I think purpose of 4 water level sensors tells controller whether storage tank has any water and how much. If you have heating elements then it decides which to turn on and how hot.

Or multiple water storage tanks. Requiring more than one sensor?

It's possible to apply analog signals to invert-gates and make them function as decision makers. It's hard to be sure if the capacitors are intended to perform a timing function or else to establish a 1/2 supply_V DC level at the inputs.
 
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hi Brad

im not interested of heating water im just looking to know how to read this sensor & how it works
i hope someone knows this information to help me
would you please guide me to understand this use of hex inverter ?

thanks
Johnny
 

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KlausST said:
it is a "temperaure-to-frequency-converter".
Very poorly designed. It relies on the precise voltage thresholds of a HC04 logic device.

Klaus
Click to expand...
hi Klaus
i've found the Senosr connections
2 wires are 10k NTC & t2 wires for 3 steps level display
but i cant see how it uses analog signal to detect water level when the mcu has no ADC input

thanks
 

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ok i see but how the hc04 helps to convert the analog read to frequency ?
give me a technique name to search for

thanks
Johnny

KlausST said:
Hi,

Then it additionally is a "waterlevel-to-frequency-converter"


"Frequency" is no analog signal ... it needs no ADC to be read

Klaus
Click to expand...
 
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KlausST said:
it is a "temperaure-to-frequency-converter".
Very poorly designed. It relies on the precise voltage thresholds of a HC04 logic device.

Klaus
Click to expand...
I don't see how this generates any frequency. In order for it to oscillate, you need an odd number of inversions in the forward path; that's not the case here.
 

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Hi,

you speak in riddles. What exactly do you see? Describe it. The parts are numbered, for a good reason.

Let´s take the upper converter, using U1: D
* It is only one (1 = odd) inverter
* and the "negative feedback" goes via R2
* I can only guess you mean the positive feedback via U1:E and C1 ... which is the timing capacitor that is used to generate the hysteresis.

Klaus
 
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johnny78 said:
hi Brad

im not interested of heating water im just looking to know how to read this sensor & how it works
i hope someone knows this information to help me

would you please guide me to understand this use of hex inverter ?

thanks
Johnny
Click to expand...
Six invert-gates on a chip. It's an easy device for designers to reach for considering it has six devices in one package (small real estate) and all six can be powered by one supply (economical). The pinout is easy to remember. By putting resistors in the input wires, they can perform a pullup-or-pulldown function, so can be used (like an Opamp or comparator) as a decision-making switch. Here's an oscillator circuit using 2 inverters. It might need adjusting to avoid start-up problems.

 

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R2 doesn’t provide any kind of feedback. The only feedback path I see is C1 around U1D and U1E, which is positive, as you noted. Are we looking at the same schematic?
 

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Hi,

barry said:
R2 goes from the output of U1D, through a variable resistor to ground. How is that feedback?
Click to expand...
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:
johnny78 said:
the sensor reads the water level 4 steps & the temp of water using 4 wires
Click to expand...
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
 

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C1 and C2 are the feedback capacitors, they set the frequency in conjunction with the fixed resistors and the temperature dependent resistors.
The MCU can determine the temperature by measuring the frequency and after the final inverters it will be a digital waveform. I agree, it will never be accurate because of wide component tolerances, especially the capacitors and to a lesser degree the thresholds of the inverter inputs.

I prefer the PWM and comparator method, far more accurate for the same number of components.

Brian.
 

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barry said:
R2 goes from the output of U1D, through a variable resistor to ground. How is that feedback?
Click to expand...
there is no variable resistor its a 18v varistor

im not intersted anymore with this ancient technique
it was the sensor i wanted to know how its wired & my guess was right

white - green is the 10k ntc
red - blue is the water level read via 3 varied resistors
now i can read this sensor with any analog input of another MCU

thanks
Johnny
--- Updated ---

KlausST said:
it is a "temperaure-to-frequency-converter".
Very poorly designed. It relies on the precise voltage thresholds of a HC04 logic device.

Klaus
Click to expand...
unfortunately there is millions of this very poorly design sold here

johnny78 said:
there is no variable resisotr its a varistor
Click to expand...
 
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