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Author Topic: ph-logger from cheap ph meter from DX  (Read 26639 times)
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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 http://dx.com/p/0-6-lcd-ph-test-pen-set-3-ag13-42734
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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 smiley what do you guys think? if this would work i could build a weary cheap ph logger





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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
« Last Edit: August 01, 2013, 07:27:17 am by esmi83 » Logged

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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:
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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}
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oh , sounds like one big job to figure this out, is there any logic way to do it?
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Bump!
Anyone?
I would really wanna know how to do this...

Quote
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
  
« Last Edit: August 14, 2013, 01:12:08 pm by Samba » Logged

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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...

« Last Edit: August 18, 2013, 05:04:55 pm by Simpson_Jr » Logged

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Did OP lose interest?
If so I guess I'll spend the big $$$ and get one to try to get it "hacked"...
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Is there any text on the chip? You need to find datasheet so you know what each pin does...
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Do you still have the LCD ?  smiley-lol

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....

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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
« Last Edit: August 26, 2013, 10:46:28 am by Samba » Logged

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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.
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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: http://www.sparkyswidgets.com/product/leophi/
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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: http://www.sparkyswidgets.com/product/leophi/
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...
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