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Topic: ph-logger from cheap ph meter from DX (Read 30464 times) previous topic - next topic

esmi83

of course if i could do that i could make several monitoring stations, the problem however is that i have limited knowledge of electronics, so i i'm somewhat dependent on a little help on the way, i really do not hawe any good tools either, like Oscilloscope etc, i only hawe multimeters.....

esmi83

http://www.sparkyswidgets.com/product/leophi/
is the microcontrollers the same?

Simpson_Jr

#17
Aug 28, 2013, 04:41 pm Last Edit: Aug 28, 2013, 04:55 pm by Simpson_Jr Reason: 1

http://www.sparkyswidgets.com/product/leophi/
is the microcontrollers the same?


:D

It probably is a microcontroller, but it is very unlikely it's an atmega32u4 as used in the link mentioned. The arduino-PH-meter-controller uses the same exterior as the chip in your meter, but internally it may differ a lot.

Looking only at their microcontrollers,  and only those using this so called tqfp-44 exterior, Atmel (producer of "arduino" chips) sells about 85 different ones and for sure isn't the only one company on the market.

Quite often texts on chips are  small /poorly readable, but with a good light and magnifying-glass it's often possible to find out what chip it is. Knowing which one it is may help you/us one step further.
The same is true for the LCD. Could you give us any info you can find on both ?

It's a pity the back is covered with glue. It wouldn't surprise me the rectangular block houses an opamp.

Samba


http://www.sparkyswidgets.com/product/leophi/
is the microcontrollers the same?
They sure look the same.
First of, I'm a total n00b!
To ease talking about the pins I made a pic where I numbered them, no idea if this is a smart way of doing it.



I think all you need is a multimeter to figure this out.
[font=Verdana]DO NOT TRY THIS UNTIL SOMEONE WITH MORE KNOWLEDGE SAYS IT'S OK, YOU MIGHT DESTROY THE pH METER [/font]
Do I remember correctly that the meter gives randon mesurment(numbers jumping everywhere on LCD) when it NOT submerged in anything? If so:
Try measuring  the pins (might be easiest at IC end) against ground, while its NOT submerged but ON.
If you get a voltage on almost all pins(we are not looking for a constant voltage, just quick pulses, as the numbers on the LCD randomly change), that would mean the LCD has common ground. Note/post the voltage. Note/post what pin/pins are 0V at ALL time, that would be ground.
If not(or only at 1 or 2 pins) it would have ground at the pins and voltage as common. Shit, I cant imagine this helping you a bit, but... I'll go one...

Lets say you get 3.3v at almost all pins, so we have com ground.
Now turn of the pH meter and take 2 of the 1,5V battery's and connect BAT- to lcd ground pin. Then connect BAT+ to 1k resistor and to LCD pins(one by one) that gave you a voltage when testing before. The 1k Ohm might be to big and the LCD segments dont light up, then you would need to change the resistor to a smaller one. Actually, I'm not even sure if you need a resistor. Oh god, this is not going to end well...
If you get the LCD segmets(you should see just one light up at a time), take note what segment lights up and what pin at that time you are applying voltage to. 
Now we would know what combination of pins for example are on/high when the LCD is displaying 1.1. This way I think you could connect the LCD pins to digital input pins(or piso) and get the reading in to your arduino.

I'm totally guessing here, I DO NOT KNOW WHAT I'M TALKING ABOUT so please, help out. 

Samba

#19
Aug 28, 2013, 05:10 pm Last Edit: Aug 28, 2013, 05:52 pm by Samba Reason: 1
Quote

It's a pity the back is covered with glue.



Back side:



Front without microcontroller:


esmi83

actually it is written something on the chip, but only kelilong's logo and "www.kelilong.com"

Simpson_Jr

#21
Sep 04, 2013, 09:57 pm Last Edit: Sep 04, 2013, 10:17 pm by Simpson_Jr Reason: 1
Seems a bit strange that a company selling mostly sensors would design its own microcontrollers. But with such numbers of meters/chips sold, printing the name may just have been part of a contract with the  chip factory. It's a pity, but that's all it is.

If you have a multimeter, you can check which voltage the chip uses to send data to the lcd. You won't harm the PH-meter by doing that.

The drawings of Samba can be very helpful.

Check 1, I do guess Black/Red wire (battery) will be gnd and positive voltage, but you've got to be sure.

Second part, check what voltage there may be between black and yellow lines.

Keep in mind there may be no difference in voltage on some yellow lines. Should one of the last two numbers displayed for example be 1, only 2 out of 7 segments will be turned on. To see all lines/segments activated one would need an impossible PH of 18.8.

Any way, once you know which voltage the LCD/segments needs, easiest will probably be to start experimenting with the LCD to check which line triggers which segment.

This is still a bit risky since I still don't know which exact LCD-display was used. I did search on 2.5 displays in the last days though and haven't found one that doesn't use a common pin and a pin per segment yet. The number of IO-lines would also perfectly fit.

Samba, if you still have your LCD, could you test it for this project ?
Looking at the board (&datasheets of other LCDs) you won't need a resistor. If you feel safer using one, each segment draws only a few microAmperes, you probably will be able to trigger a segment using a resistor of 10k or higher.
Once we know which line triggers which segment we can almost start programming.

By the way, one thing that came to mind after seeing the meter without chip is that you may... still be able to read the meter. The PH-sensor itself gives a very small voltage, the opamp translates it to a higher voltage after which it is read by an ADC in the microcontroller and printed on lcd. What we've tried so far is looking at the output of a microcontroller, but you can try to read its input as well.
Arduino has an adc as well. If you can find the right pin, it may be possible to analogread it with your arduino.

Samba

#22
Sep 05, 2013, 04:10 pm Last Edit: Sep 05, 2013, 04:13 pm by Samba Reason: 1

Samba, if you still have your LCD, could you test it for this project ?


Unfortunately I don't have it no more. But one is in the mail from China, so I'll have a new fully working one "soon".


By the way, one thing that came to mind after seeing the meter without chip is that you may... still be able to read the meter. The PH-sensor itself gives a very small voltage, the opamp translates it to a higher voltage after which it is read by an ADC in the microcontroller and printed on lcd. What we've tried so far is looking at the output of a microcontroller, but you can try to read its input as well.
Arduino has an adc as well. If you can find the right pin, it may be possible to analogread it with your arduino.


The sensor part is removed as well, so I'll just have to wait.

What about OP!
Are you still around?

Edit:
I should learn to use kicad or something and make some "proper" drawing of the circuit

esmi83

yes i am here, but i hawe also broke apart the sensor... i have the lcd though but i do not know how to test it..... I have no tools, only a multimeter.


Samba

I got mine in the mail, but been busy. Ill try to chop it up soon...


femur

i have just ordered one of these
http://www.dfrobot.com/index.php?route=product/product&product_id=1025

seems easier than ripping a meter apart! (although not as fun)

:)

Femur

esmi83


AndrewR

An easier alternative....

A pH meter is simple a voltmeter with a very high input impedance. The output of a pH probe is around -27mV per pH unit.
An easier way to do this would be a High input impedance amplifier with some gain and offset to suit the 0-5v analog input on the arduinos....

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