Matrix Orbital Corp

I have an old (new in box) VK204-25 VFD that is revision 1.23.

I am having issues getting the VFD to do anything via i2c, everything works fine with the built in RS232 connector.
I have tried every manner of getting some kind of command to work over i2c, but nothing. I cannot even see the device with an i2c scanner.

I noticed the newer revisions of the boards have jumpers to select between rs232 / i2c, but the only thing my board has seems to set both the Baud rate as well as the i2c address with no mention of choosing one or the other.

Am I missing something here, I have spent quite a few hours with no results.

The manual doesn't specify that I can see, but is any pullup needed on the data and clock lines?
I read somewhere, maybe a newer revision manual that 1k - 10k pullup can be used, but I don't see anything of the sort for my display.

Hi Phantax,

Yes, a pullup will be needed on both the data and clock lines.
Also the 4 pin header is for I2C only.

I am currently working to replicate the issue you are having to further trouble shoot as well.

If you have any other questions or concerns please feel free to ask.
Thank you,
Martino

I have tried both the internal pullups of an Arduino Uno as well as external 1k pullups on 5v and have no luck either way so I don't think it is that.

Hi Phantax,

I have replicated the issue you were having with the VK204-25 Rev 1.23 and got it working with the setting I previously given you.

When using Arduino the I2C is set to a 7 bit address instead of a 8 bit.

Attached to my post is a Working I2C Scan. Please note that it is set to look for our full range of addresses listed in you manual.

If you have any other questions or concerns please do not hesitate to ask.
Thank you,
Martino

Hi Tino,

Can you confirm your jumper settings, I have J1 and J2 on which is the default.
The address should be 0x5C (8 Bit) -> 0x2E (7 Bit), 19200 Baud
Are you using the internal pull ups on the Arduino?

It seems like whenever I have the display attached it blocks execution on the Arduino
If I start the scan it hangs here:

***
Scanning I2C bus:
40

As soon as I unplug the clock and data lines, execution continues

41
42
43
44
45
46

Sometimes I will need to reset the Arduino to make execution continue.
Are the i2c headers exposed anywhere else on the board? Is there an in line resistor somewhere I can check on the i2c lines maybe?
The reason I ask is the problem can be duplicated by shorting the clock and data lines on the Arduino when the scanner runs with no display attached

Hi Phantax,

My jumpers are also on J1 and J2. Also I am using Internal pull ups on the LK204-25 itself.

I am using a Arduino UNO Rev 3. My SDA and SCL lines are connected to the Analog 4 and 5.
SCL line is connected in A5 and SDA to A4.

I've attached a photo of my Arduino to show how I have my display connected and a photo of where the pull ups are located on the display.

Where the pullups are on the display is where you may be receiving your short.

If you have any other questions or concerns please don't hesitate to ask.
Thank you
Martino

My board seems to be populated with quite a few different components than yours.
Also, the solder pads next to the J0 - J3 jumpers on yours are bridged, mine are open.

Hi Phantax,

Yes My display is populated slightly different than yours. Reason being is i am using the LCD model and you are using the VFD model. So the components that are on my display are for powering and controlling the back light.

Did you find any shorts on your display?

if you have any other questions or concerns please feel free to ask
Thank you
Martino

I am still looking for shorts, but I will admit it is a little hard to check everything as the two boards can't be separated without desoldering and it appears that at least some of what I would be interested in is sandwiched in the middle.

Could you check the resistance between the clock and data lines and tell me what your display reads?

Hey Phantax,

The reading I have for my resistance between my clock and data lines is 4.4k. I have 2.2k on my pullups, which are in series.

You shouldn't have to separate the PCB from the screen.

If you have any other question please feel free to ask
Thank you
Martino

Hi Tino,

Any other suggestions to check? Do you have a VFD version of this board you could compare to my photos?

As you can see there are no pullups on my board where they are on yours. The screen works fine over a serial port, I assume if there was a short on the i2c bus, then the screen wouldn't work at all, but I may be wrong. Does the serial port connection use the i2c bus internally?

Seems to me its definitely a hardware / setup issue of some type, I cant even see anything happening on a logic analyzer, both lines just stay low. I have tried a few other i2c devices and have no issue communicating with them at all.

Hi Phantax,

The reason you are receiving a low signal from your I2C lines is because there are no pull ups on your board.
You will need to populate the pull ups in order to use I2C, please do so. Let me know if it works after you do so.

The serial port and I2C use separate lines. The I2C goes directly to the controller.

If you have any other questions please feel free to ask.
Thank you
Martino

While I cannot find anything in reference to resistors in the manual for revision 1.23, I see in revision 3 the following:

. Connect the Breadboard Cable to the Communication/Power Header on your LVK204-25 and
plug the four leads into your breadboard. The red lead will require power, while the black
should be connected to ground, and the green and yellow should be connected to your
controller clock and data lines respectively.
b. Pull up the clock and data lines to five volts using a resistance between one and ten kilohms on
your breadboard.

I have tried external pullups all the way from 1K to 10K and also tried populating the board in the spaces where yours is populated, still no luck.
I think it is time to call it a day on this one unfortunately.

Hi Phantax,

I'm sorry to hear that after using the pull-ups your I2C still did not to work.

This could be because there is damage to the display. But i can't say this without further analysis.
With that being said, considering the age of your display it would most likely be cheaper for you to purchase a new display rather than sending it in for repair.

If you have any other questions please feel free to ask.
Thank you,
Martino