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need help -is it possible?

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hazic

New Member
I have a simple device with a small LCD that according to a sensor connected to it displays a number between 000 to 999. i have something i'm trying to do and to do it i need somehow to interface to that number on th LCD and get it into a MCU.
Do you think it is possible to interface this little circuit and get this number?
if you need a better photo i can try picture it again.****edit new photos

back side

front
 
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hazic

New Member
I've changed the photos in the first post...

What i'm trying to do is to compare that number with a value i choose and according to the result close or open a relay. for example lets say the value is 50. so if the result on the LCD is greater than 50 the relay is closed and if it is below 50 the relay is open.

SW1 is power on/off
SW2 is switching between sensor 1 and sensor 2. (sensors are connected to the connector above with the 8 wires. white and red to sensor 1. blue and white to sensor 2. i'm only interested in one of the sensors.)

BTW this device is testing tap water quality in TDS units.
 
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Dotnet

Member
Hi Hazic,

I'm not giving an answer here (because I don't know) I'm just posting how I would 'think' about the problem given the info you supplied.

Looking at the number of via's under display on the bottom of the boards I'm guessing it is not a serial display device (but the possibilty can't be dismissed). The IC under the black splodge might be identifiable because they have chosen to hide it - research needed (by careful scrapping/filing)

One way would probably find out what sensor they are using to feed the board (voltage/current etc) and take off from connector soldered to the board. The problem is making sure that there is no loading on this CCT to affect the reading.

Probably the easiest way is to research the display connections and consequently take connections off from the via's (if you have access to all of them!!) and not forgetting buffering - probably high impedance (FET)
Do some research on LCD displays try to find one which matches the physical dimensions spec etc of this one - at least you can narrow down what those via's might be connected to. (RS Components)

Don't forget this probably uses some form of multiplexing to control the relevant digit on the display so timings are going to be your problem - oscilloscope needed

Hope this helps
Matt
 

Sceadwian

Banned
It's definitely not serial, not for a 7 segment display. And the blob isn't hiding the IC, the blob IS the IC. They bond the raw silicon chip directly to the PC board and throw the blob on to protect it, no carrier package expense that way, many cheap asics do that.

Why do you need to read the LCD itself? Why can't you just tap the incoming signal lines and read what you what directly and get rid of the pesky board in the first place? A decent general purpose IC is going to be pretty much garunteed to be able to perform whatever function that cheap dot is doing.
 

Dotnet

Member
"And the blob isn't hiding the IC, the blob IS the IC. They bond the raw silicon chip directly to the PC board and throw the blob on to protect it, no carrier package expense that way, many cheap asics do that"

I stand corrected - thanks for that

Matt
 

microtexan

New Member
I've changed the photos in the first post...

Much much better, thanks.:D
 
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hazic

New Member
Thank you all for your answers

Why do you need to read the LCD itself? Why can't you just tap the incoming signal lines and read what you what directly and get rid of the pesky board in the first place? A decent general purpose IC is going to be pretty much garunteed to be able to perform whatever function that cheap dot is doing.

because i thought that reading the LCD will be easier than building the whole circuit myself...

BTW the sensor is measuring the waters conductivity. it has 2 pins on the water side and 4 wires to the circuit. i will add a photo later...
 
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Sceadwian

Banned
hazi, reading the LCD itself is going to be harder than replicating the entire circuit, depending on what it does. Post some details about the sensors you're using and a few more photo's wouldn't hurt, I love looking at projects rather than just reading text.
 
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hazic

New Member
I don't know how the sensors work, any idea?
i try to meause the wire for resistance or voltage changes with no success.
I thought maybe if i can out a comparator parallel to the sensor's connection to the circuit and adjust it to the value i want maybe it can do the jub...
 

lasielle

New Member
Hi hazic,

Far easier to duplicate what the circuit and sensors are doing yourself, then you can do what you want with the signal.

I have seen someone interface to the connections on an LCD display, but it took a long time to do, and they had no choice.

Just looking at the board, it can't be complex. TDS will be total dissolved solids, so it is looking for dissolved salts and will be measuring conductivity. If you look around the web, you'll find some resources for dissolved salt measurement. A few devices I've seen use carbon electrodes.

It's going to be far easier to reproduce what your circuit is doing, then put your own analogue signal into your own microprocessor system - far easier. That way, you'll only have to reverse engineer the relatively simple analogue measurement system. I suggest that you try a varied of resistors, or a resistor substitution box on the electrodes t get an idea of the calibration curve it uses.

Hope that helps.

Cheers, Colin
 

dougy83

Well-Known Member
You probably can. The sensor will need to be in the water though...

There is 4 wires going to the sensor, so my guess is that the sensor is wired in a similar fashion to other 4-wire sensors: 1 pair used to pass a regulated current through the water, while the other pair are used to monitor the voltage across the electrodes.
 
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hazic

New Member
I checked for changes in voltage and resistance on the electrodes while changing the measured value(outside the water "000" in the water i get "780") and i didn't see any noticeable chage...
 
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hazic

New Member
I checked for changes in voltage and resistance on the electrodes while changing the measured value(outside the water "000" in the water i get "780") and i didn't see any noticeable chage...
 
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