ph-logger from cheap ph meter from DX

hello
i wonder if you guys think it is possible to log the results from a cheap ph meter using arduino? if i open one of these for example Professional 0.7" LCD Pen-type US Conductivity Meter - Blue - Free shipping - DealExtreme

here are some really bad pictures of the opened tester, my thougt vas that if i could solder some connections somewere i could hoock it up to the arduino logger, but i hawe newer done something like this before :slight_smile: what do you guys think? if this would work i could build a weary cheap ph logger

here is from under the display

http://home.zonnet.nl/rsetteur/aquarium/karel/ph/ph_images/lf444.gif

maby if i vould find "ph out" (see picture in link) in my dx pen i could log that result....

http://damien.douxchamps.net/elec/ph_meter/

another good page

I actually got one a year ago, cut it up thinking I could reverse engineer it, but the project never got of the ground.
Still got the board, without microcontroller. If you need pic without, I can post one.

If I understand it right, it has a pin for every "line" on the 8 display, if you connect them to your arduino you could get a reading like that.
Sorry for my English

Hope this helps:

Samba:
I actually got one a year ago, cut it up thinking I could reverse engineer it, but the project never got of the ground.
Still got the board, without microcontroller. If you need pic without, I can post one.

If I understand it right, it has a pin for every "line" on the 8 display, if you connect them to your arduino you could get a reading like that.
Sorry for my English

Hope this helps:

Stupid example:
if (A && B && C && D && G)
{pH =3}

oh , sounds like one big job to figure this out, is there any logic way to do it?

Bump!
Anyone?
I would really wanna know how to do this...

oh , sounds like one big job to figure this out, is there any logic way to do it?

Most likely the pins are in a logical layout on the board. I would guess A=1,B=2,C=3 or A=10,B=11,C=12 or something like that.
One thought is to try to connect a voltage to the display and see what light up, and that way "reverse engineer" the pin layout.

Do you still have the display intact/working?

Does it have common cathode or anode, NO IDEA.
I would guess its 5v, but PLZ don't trust me, I really have no idea about this stuff. There is no resistors between microcontroller and display, do all mircocontrollers output 5V or 3.3V? Dont know that either...

I would love to know what microcontroller is used on this board, but I think that's impossible to find out...

PLZ people with the knowledge, come help out!
EDIT: It runs on 3 x AG13

EDIT:
I have the same pH meter without the IC
Don't know if this helps:
http://www.pictureshack.us/view_50227_pH.jpg


For some reason I dont seem to be able to post pics...
There's one "line" with 2 dots, that's the only one connected to 2 pins for the display, so I could and would guess that that's the common cathode or anode...
Or it might be the 1x.x

EDIT:

So it a 18.8 display, you cant display 28.8 on it, the first number is only 1 or off. I guess you could say its a 0.0-19.9 display

Officially it's called a 2.5 numerical LCD module/display. For some reason the 1 is seen as .5
A 3.5 module like wise will display a number up to 1999.

Looking at datasheets of numerical lcd modules, quite a number have a common pin (often gnd)
and a pin per segment.

2 x 7 segments + dot + "1" + common in that case results in minimum of 17 pins.

Since 2 lcd-lines on the picture apparently are the same (black line) and the footprint is 18 pins big, it might as simple as checking all 16 lines and reconstructing the PH-value depending on which lines are high/low.

If I'm right, it should be possible to use the LCD itself, check which segments are shown when you
apply a voltage to specific pins. (I'd start low in case it's 3.3 volt display and check whether the common pin is actually connected to gnd or a positive voltage first)

You should of course google any info you can find on the LCD first and keep in mind I may be totally
wrong...

Did OP lose interest?
If so I guess I'll spend the big $$$ and get one to try to get it "hacked"...

Is there any text on the chip? You need to find datasheet so you know what each pin does...

Do you still have the LCD ? XD

I do wonder how many different PH-meters are built using the famous red and yellow exterior. I know they're sold by brands like hanna, but they're also sold by truckloads with no brand-name. Since they have been on the market for at least 25 years, you may as well find a black blob on the pcb if you buy one.

I'm interested as well and have got a brandless tomato-red one. But I probably have to sleep on the couch by now, should I need to buy a backup, we're low on finances. If only they had used screws instead of welded plastic....

I think OP gave up on his hack....
~~I'll place a order for one today.~~I just ordered one from ebay.
I was thinking, if pins for tens (the first (1) one, 1x.x) would by the LCD text on the PCB, might I be able to get 0.0-9.9 from the lower pins?
I might be able to get a 16bit PISO shift register on it. I would have to bend some of its legs leads up and use some wire to get some of the pads and pins leads connected, but it might be possible to connect the pH meter to just 1 digital pin on my Arduino, or would it?

Edit:


If I could just find a wider IC

If (!) the lcd uses a segment per pin, you could indeed read it with a 16 bit piso-shiftregister.
A shift register usually uses 3 lines btw.

I wouldn't solder one on the LCD-pads of the PCB yet in case I'm incorrect.
Even if... it uses a pin per segment, you should be sure you're lucky the input lines of the register match the pin-out of the LCD. Soldering the extra wires to power and command the chip also seems quite difficult.

I'd probably try to solder thin wires to each LCD-pad and use an arduino to check further first.
If it works I'd use a big blob of hot glue to keep the wires in place/assure there's no tension and consider the PH-meter a prototype.

If... it uses a pin per segment you could use a shift register, but using an Atmega8 (oldest arduino, $1.20-chip) may be interesting as well.

It has enough pins to read the meter and gives you the possibility to create an intelligent PH-meter readable by rs-232, rs485, I2C, SPI (shiftregister) or other protocol. If it would keep a pin high for PH-value x milliseconds every 15 milliseconds, you could even read it with one pin.

Oh i had nearly given up, the PH meter is made by a chinese firm (kelilong), the component looks like the one they hawe used in this board: LeoPhi - Sparky's Widgets

esmi83:
Oh i had nearly given up, the PH meter is made by a chinese firm (kelilong), the component looks like the one they hawe used in this board: LeoPhi - Sparky's Widgets

That looks sexy, but 30$ + you have to get a probe, but still, SEXY!
Are you still up to hacking your meter? Mine will arrive in about 3 weeks or so...

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.....

is the microcontrollers the same?

esmi83:
LeoPhi - Sparky's Widgets
is the microcontrollers the same?

:smiley:

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.

esmi83:
LeoPhi - Sparky's Widgets
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.
DO NOT TRY THIS UNTIL SOMEONE WITH MORE KNOWLEDGE SAYS IT'S OK, YOU MIGHT DESTROY THE pH METER
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.

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

Back side:

Front without microcontroller: