2004 20x4 I2C Serial LCD Module (HCMODU0010)

[Jānis]

See missing pins

[andrew]

I think its best to give a little explanation of why this is an issue on Arduino boards even though it is a little off topic for this thread. The I2C interface, like the SPI interface is a common 'gotcha' on Arduino boards because they appear in different places on different versions of board. This is because different Arduino boards use different versions of microcontrollers which in turn have different hardware configurations including the location for the I2C interface. As a result the I2C interface appears in different places on different Arduino boards even though they have a standardised connector configuration and pinout. In Arduino's latest reference design update (revision 3) they attempted to address this issue by adding additional pins to the standardised connector layout including the SDA and SCL pins which you show in your picture. These additional pins did not exist in previous versions of Arduino boards and any shields designed before this latest update will not include them. At this current moment in time it is likely you will get this issue with most shields not specifically desinged for R3 Arduino boards. As with the MOSI interface it is something that should be considered when choosing shields not specifically designed for the version of Arduino board you wish to use it with. Your point about making this clear for the V4.0 shield is very valid and we will update the description for it.If you have not modified your shield would like to return it for a refund you can contact sales at hobby components dot com.

[Jānis]

Thank you for confirmation. I am not deep in Arduino world, - my conclusions might be wrong.
I agree regarding off topic, but this is a good a reason to make chapter in forum for SS V4, which is missing...
As it is my fault (not dug in details) I am not going to send it back (but I just ordered UNO, which is compatible... - to use this set for another project)
I also would be fine to provide references to architecture documents - in any case plate, module... is developed by smbdy and then cloned by a lot of manufacturers. For example, sensor shield has number of LEDs, but i still are unable to find description about them. The same was about jumpers- I discovered difference by looking on photos and then started to think about meaning of them...

[andrew]

We don't currently have a thread for the V4 sensor shield but it is on the list. The shop listing is due for an update with more information but unfortunately the manufacturer of this shield doesn't supply a schematic. We will try contacting them again and see if we can push for one. If so it will be made available in the Arduino shields section of the forum.

[AndyBTW]

Hi Andrew - thanks for your patience dealing with all these 20x4 serial LCD issues - I was able to sort our my problems in just a few minutes when I found this forum. I just wanted you to know that your effort is REALLY appreciated. I also learned about the two new SCL and SDA pins on the latest Arduino Uno.

Warm greetings from the Western Cape in South Africa.
AndyBTW

[andrew]

Welcome to our forum and glad to hear that it was able to help you. We are trying to dump as much knowladge and information as we can on here but its a slow process. Btw, we do get lots of customers from your part of the world

[daniel1111]

To hopefully save someone else some grief - I've just purchased one of these modules from the hobby components ebay store, and found that the I2C address was set to 0x3F, not 0x27 as per the examples I've seen (identified using an I2C scanner Arduino sketch). I was in the fortune position of replacing a failing display (first two lines worked, the second two mostly no longer did), so was fairly confident the code/connections were good.

[andrew]

Thanks for the heads up on this. I've just pulled one from our latest batch and it seems that there is an update to the I2C adaptor board on the back. The update adds 3 address selector pads which in turn effect the lower 3 bits of the I2C address. Where boards from older batches had these pins grounded giving a default address of 0x27, the new update leaves them pulled high giving a default address of 0x3F.

I will update the first post to reflect this.

[Langster1980]

Having problems with an 20x4 I2C display I bought recently. It doesn't respond at all. I have checked the example with both addresses. The screen itself powers up and the backlight comes on when prompted but no characters are displayed on screen. I then tried another I2C device (An RTC) with the same wiring and the arduino I2C scanner:

http://playground.arduino.cc/Main/I2cScanner

That worked perfectly and gave a sensible response so I know it's not my wiring or the code, which suggests I have a faulty module. Has anyone else had any problems recently?

[andrew]

Are you using it with an Arduino? If so the first thing to check is the library. It's important that you use the correct version of library for the display you have. Did you buy it from us? If so then are you using the library in the first post of this thread? If you bought it from elsewhere you'll need to make sure that you have the appropriate version of library.

The next thing to check is the potentiometer on the back of the display. It sets the contrast and will need to be adjusted when you first receive it otherwise you won't see any text like your reporting.