Manufacturing ...

[BigWumpus]

Hello,

I have a problem:

Our controller V3 works great (maybe 3000 parts in the market) with our display V3. They communicate via I2C (16F876 - 16F872). The producer has soldert a lot of 2,7k pullups and at last 4,7k pullups (poland...).
They work great!

Now, we have our display V4 (+PWM for LCD +RGB-backlight) and it works great with controller V3.
Our controller V4 (18F4585) works great with both displays.

The software is nearly the same...

Yesterday we have a problem:
The I2C-communication is bad. A display V4 works on controller V3 but not really on a controller V4. (MSSP receives no bytes)
Sometimes I put my hand over the display - it works, or I touch the display - it works - or not...

Yesterday night i checked out the software. I set down the speed of the I2C to maybe 60kHz - it works. Back to 100kHz - it works. Up to 300kHz - it works. ???

Today I checked again...
A few days ago we have changed the pullups from 4,7k to 3,3k - that may be the problem. But all people tell, the lower the pullups, the better the signal. (signal form is ok). Inserting 10k pullups - it works. And why does the 2,7k pullup worked so well ?

Where is my problem ?
Pullups to low ?

[Melanie]

I find 4K7 pull-up's good from one device on the I2C Bus, right up to about 8 devices on the I2C Bus. Have you put a scope on the Clock and Data lines to see how clean and square the pulses are?

If you are putting your hand over the product and it affects how it works, looks like a decoupling/noise problem. Your I2CBus is pretty resilient and should not be affected. You may need at add some 100nF's around your Vdd and perhaps improve the grounding. It is possible the problem is not with your display, but with your controller. The 18F's are a lot more intollerant of noise. Another thing to look at is if you are using a crystal, if it's being used in weak XT mode instead of HS mode (higher level of drive), your hand approaching it may just add enough extra capacitance to stop it from working.

PS... message me off-list, I'd like to know who you use to manufacture in Poland, what they're build quality is like, and how cost effective they are to use. Obviously the labour is cheaper than Germany, but how much cheaper? Always looking for good intelligence on where to get things made cheaper...

[sayzer]

...Always looking for good intelligence on where to get things made cheaper...

Goto Here!


Here:
Where I am.




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[Melanie]

Soon... but not yet Sayzer... Turkey is not in EC yet, which means shipping parts to and from a non-EU country is prohibitive on Customs paperwork and this negates the savings made in lower-cost labour.

[sayzer]

Please allow me to provide the following information.

On 31 December 1995 the customs union between Turkey and the European Union came into effect. Goods can travel between the two entities without any customs restrictions.


http://en.wikipedia.org/wiki/EU-Turkey_Customs_Union
http://www.gumruk.gov.tr/english/con...3&cId=b_origin

and also pls visit http://www.deltur.cec.eu.int/english/ei-gumruk.html


Lets negotiate Melanie! :-)



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[Melanie]

I will send you details to quote by PM... gimme a couple of days to organise the specification and get some pictures taken so you know what's involved...