Hardware Design and Development

[Penri]

Spliced in a 900mm length of multi-core cable between the display module and RPi to see whether there would be any degradation of the displayed image.

As far as I could tell the image was unchanged, which is good news.

[TerryJC]

It certainly is! Does your version of the hardware have the pull-ups on the Veroboard?

Obviously the inability to drive more than three screens has nothing to do with the length of the SPI Bus.

[Penri]

No pull-ups fitted for my trial, although I did use a vero board to make the joints at the display module end just in case I needed to add some.

[TerryJC]

Here is the board that I've used. Upper Side:

Tiny_TV_Screen_Upperside.jpg (84.15 KiB) Viewed 705 times

and Lower Side.

Tiny_TV_Screen_Underside.jpg (134.65 KiB) Viewed 705 times

That board can be made smaller if need be.

[Penri]

Just picked this up this post.

The TinyTV chassis would not be able to accommodate the pull up board in the orientation shown. In order to achieve something like scale everything needs to be more or less within the height and width profile of the display module itself; depth behind the screen is not an issue, some 30mm of void is available.

[TerryJC]

OK. I'll look into that.

[TerryJC]

Penri,

There are two easy solutions to this. The first is to simply flip the Veroboard over so that the component side is upwards. I would need to fit extended Pins to enable the base of the board to clear the underside of the Screen PCB, but that shouldn't be too difficult

The second solution to this is even easier; dispense with the terminating resistors completely. You appear to have shown that they're not needed, so unless we were planning to put the screens a huge distance from the boards, I doubt they would have any benefit anyway.

What do you think?

[Penri]

Terry

Dispense with them I'd say.

Provided my observations with the Pi I have are borne out with an installed set-up, I think we'e on to a winner!


Penri

[TerryJC]

In preparation for the build which will recommence this weekend (viewtopic.php?f=39&t=288), I have updated the Circuit Diagram and Layout Drawing to remove the fourth Screen connector. See attached.

[TerryJC]

I've just discovered an error in the design of my Tiny-TV Interface Board which may account for the inability to drive the fourth Screen. When I allocated the GPIO Pins to the Screen Select lines, I inadvertently allocated the Screen 4 Select to the same pin as the OLED_RST. This reset never seemed to work, even when I wasn't trying to drive more than one Screen, but it is still toggled inside the OLED_Driver code.

I am in the process of redesigning the Board to use a different GPIO Pin for Screen 4 and re-instate the OLED_RST pin on each screen. I will then update the software and see if the fourth Screen comes to life.

I should still be able to complete the build by the end of the month as agreed. If not, there should be enough Interfaces working to make a start on the population of the shops.

I'll post here when I know the outcome of the changes.