tc1121cpa

[Bostjan Sagadin]

Hey guys.

I finally finished my PCB (laser printer diy method) and got it almost perfect. I went to the store and got all parts except for the IC2.

I tried surfing the web and all the online stores have unreasonable shipping cost to my country (Slovenia in Europe)...I really don't think, 40€ for shipping this little IC is a good price :(

Is someone out there so kind, that can buy this part for me and send it over snail mail?

I can pay in advance with paypal or money transfer.

Please.

Thank you

Best regards

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Boštjan Sagadin

[Carlos Neves]

The IC TC1121 can be replaced by the ICL7660, ICL7660A, or ICL7660S. The ICL7660S is a direct replacement for the industry standard ICL7660 offering an extended operating supply voltage range up to 12V, with lower supply current. But, you need left the low voltage LV pin (pin 6) not connected. Just rise it or cut it.

TC1121 from Microchip

http://www.microchip.com/wwwproducts/Devices.aspx?dDocName=en010559

ICL7660S from Intersil

http://www.intersil.com/products/deviceinfo.asp?pn=ICL7660S

ICL7660 / ICL7660A from Intersil

http://www.intersil.com/products/deviceinfo.asp?pn=ICL7660

Carlos A. Neves

2011/1/14 Bostjan Sagadin <bostjan...@gmail.com>

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[Bostjan Sagadin]

Thank you very much.

My dealer have ICL7660.

Best regards

Bostjan 

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Boštjan Sagadin

[Bostjan Sagadin]

Hey Carlos.

I have now the ICL7660 at home. As I understand, it is a direct replacment for TC1121CPA ? Or do I have to modify circuit?

Thank you in advance

Bostjan

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Boštjan Sagadin

[Carlos Neves]

You need left the low voltage LV pin (pin 6) not connected. Just rise it or cut it off.

Best.
Carlos A. Neves

2011/1/18 Bostjan Sagadin <bostjan...@gmail.com>

[Bostjan Sagadin]

Thank you.

Will report soon.

Bostjan

[Bostjan Sagadin]

Hello. I'm back with a new problem.

I uploaded the software to duino, attached the pH probe.

Now it reads:

25,0°C     pH:14.42

-439mV   AD:849

Any ideas what could be wrong? I tried to play with botr trimpots, buth itout any change. I also checked my pH probe in my old pHmeter, and it works fine.

Thank you very much for your help

Best regards

Bostjan

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Boštjan Sagadin

[Carlos Neves]

Hi Bostjan,

A suggestion to test the pHmeter is mount a dummy pH electrode using a trimpot (maybe 10k ohms) powed with a symmetric voltage (from the shield) and sensing the central terminal (connected to the input sensor). In this case, the ground is the reference.

With this dummy electrode, you can apply any voltage between -500mV to +500mV. Adjust it to zero, using a multimeter, and make the adjusts.

Carlos A. Neves

2011/1/19 Bostjan Sagadin <bostjan...@gmail.com>

[Bostjan Sagadin]

Hi Carlos.

Maybe I'm a little bit closer to a solution. I found out now, that my LED 2 is not on, so there is no -5V on, as I read in your manual. Any thoughts about this?

About your previous suggestions: I don't quit understand, how to make a dummy probe. Can you please explain it in more details (maybe a drawing)?

Thank you so much

Bostjan

[Carlos Neves]

2011/1/22 Bostjan Sagadin <bostjan...@gmail.com>

Hi Carlos.

Maybe I'm a little bit closer to a solution. I found out now, that my LED 2 is not on, so there is no -5V on, as I read in your manual. Any thoughts about this?

In this case, your negative charge pump is not working. May you should make a test with it using a breadboard.
 

About your previous suggestions: I don't quit understand, how to make a dummy probe. Can you please explain it in more details (maybe a drawing)?

Let's suppose a trimpot. It is a adjustable resistor.

1/2W Rectangular Cermet Potentiometers
http://www.futurlec.com/Potentiometers/CERMR10K.shtml

If you power it with a symmetric power at the ends (-5V to the terminal 1 and +5V to the terminal 3), when you set it at the middle, you will have 0V at the terminal 2. Connect it to the pHmeter input using a male BNC connector. You can use the symmetric power directly from the pHduino shield.

http://www.futurlec.com/ConnBNC.shtml

The pH sensor generates a voltage  referenced to a internal chemical electrode. For a normal pH sensor, you will have something -350mV to +350mV to pH from 0 to 14. You can simulate it using this potentiometer powered with a symmetric potential.
 

Thank you so much

Bostjan

You are welcome.
Carlos A. Neves

 

[Bostjan Sagadin]

Hey Carlos,

thank you very much for your help so far.

I managed to get it working...but must admit I had a bit of luck.

I figured out, that it is working, if I turn the gain trimpot (R2) almost all the way down. There I have about a turn and a half to configure it... You can imagine, how hard it is. I don't know, why is it so?

Also, if I measure with voltmeter, it reads form 2,07V to 4,08V.

All of the parts in my board are as listed, except for the R9, which is 39 ohms in my case. Could this be the problem?

Thank you for any ideas

Bostjan

[Carlos Neves]

2011/3/16 Bostjan Sagadin <bostjan...@gmail.com>

Hey Carlos,

thank you very much for your help so far.

I managed to get it working...but must admit I had a bit of luck.

I figured out, that it is working, if I turn the gain trimpot (R2) almost all the way down. There I have about a turn and a half to configure it... You can imagine, how hard it is. I don't know, why is it so?

R2 determines the gain of the signal. It is the slope of the line. R3 is the intercept of the line. I wrote a procedure to calibrates the pHmeter using a pH glass electrode. If you don't have one, mount a dummy electrode. I described it some emails before. Did you mount a dummy electrode?

http://code.google.com/p/phduino/wiki/OperationManual
 

Also, if I measure with voltmeter, it reads form 2,07V to 4,08V.

Did you check if you have -5V at the terminal of the operational amplifier?

Did you connected something at the input sensor? In case of the dummy cell, what is the electric potential that you are applying? You should be able to adjust the trimpot from negative values to positive values. Use a multimeter to test it. In case of a pH glass sensor, you need prepare buffer solutions.
 

All of the parts in my board are as listed, except for the R9, which is 39 ohms in my case. Could this be the problem?

No. The voltage divider defined by R9 and R10 is to generates a voltage reference near of 2V. The firmware reads the reference voltage. The pH range from 0 to 14 will fit from 0 to 4V. For a neutral solution, pH 7, the output will be about 2V.

Thank you for any ideas

Bostjan

Regards.
Carlos A. Neves
SMILES: CN1C=NC2=C1C(=O)N(C(=O)N2C)C
 

[Bostjan Sagadin]

Did you check if you have -5V at the terminal of the operational amplifier?

Yes, I did. I checked in on the same connector, as I then connected the dummy trimpot and there is -4,88V and +4,67V, so this should be OK, right?

 

Did you connected something at the input sensor? In case of the dummy cell, what is the electric potential that you are applying? You should be able to adjust the trimpot from negative values to positive values. Use a multimeter to test it. In case of a pH glass sensor, you need prepare buffer solutions.

 

I connected the dummy probe, as you can check on my picture. I then measured the voltage on analog pin0 and GND. If I set the dummy probe to 0V - pH7 - I can adjust the voltage from 2,07V to 4,08V. If I set the dummy probe to -1V, I can adjust voltage from 2.33V to +4.08V... Its allways from around 2V to 4V. I also measured the voltage on analog pin 1 - vref...and it is allways 1V.

Any clues?

Thanks

[Bostjan Sagadin]

The picture of my wiring 

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Boštjan Sagadin