7" LCD with Pi3, using images from SD Card


#1

Exactly as title - I currently use a PIC32 and SSD1963 to display 800x480 24 bit images which take around 5secs to load due SPI limitations. Can the Pi do a whole lot better?
I’d like to know before committing time to other aspects of moving to Pi. Any useful links?
GrahamB.


#2

I suspect the Pi can do considerably better, I haven’t driven anything quite as big as 800x480 with 24bit images, however. You’d need something on the order of a 10Mhz bus speed to get 1fps if my maths isn’t totally wonky. The Pi is capable of this ( some people use higher speeds to refresh APA102 pixels via the SPI bus ), I imagine it’s something you’d want to implement in C: https://www.raspberrypi.org/documentation/hardware/raspberrypi/spi/README.md

Is there a specific reason for your display/controller/bus choice? The Pi would run rings around it outputting to an HDMI display or the official 7" Touchscreen.


#3

Hi Gadgetoid
Thanks so much for the instant response. I have been using VGA to date,
transitioning from 320x240 to 800x480 with SSD1963 and the boss says too
slow. Newhaven display clocks at 50KHz max.
I have the official 7" Pi Touchscreen and assumed it too was VGA : what
is it?
Thanks for the link. I will start from there to find the full API for
the display.
I’ll check out HDMI displays too.
Thanks again, Graham.


#4

The official Pi Touchscreen is connected via the DSI connector on the Pi itself. The signal from the Pi to the display board is DSI ( Display Serial ) and then converted on the display board to DPI ( Display Parallel ) so it’s a fast, crisp and completely digital signal path. The display is 7" ( as the name suggests! ) and 800x480, 24bit and 60fps.

You would need a B+, Pi 2 or Pi 3 to get hassle-free interaction with the display, but setup is as simple as plugging in the ribbon cable and the Pi does the rest.

Once set up, there will be a dozen different ways you could display anything from still images to full video.

The big downside is the cost, although displays of any type aren’t particularly cheap so I don’t think it would be a huge step up.

There’s also the 5" HDMI display. You will get similar performance, the same resolution and a smaller screen size ( and no touch input ) from this display, which I’m a big fan of- https://shop.pimoroni.com/products/hdmi-5-display-backpack-without-touch

You will need a USB power cable ( full-sized USB to microUSB ) and an HDMI to HDMI cable to go with it, but all-in I think it would be cheaper per unit than the official display. It’s a balance of cost/features I guess!

Either way you go, I’ve probably got some useful tips, tricks or code, so keep me posted!


#5

Thanks for your guidance. Graham


#6

Thank you for cluing me in: I have been way overfocused on my current
design approach.
RPi3B will suit perfectly for new front end on one of our instruments
and may well subsume most of the computation from the main PCB processor.

Can you help me with a power connection question?
I want to take the whole GPIO connector to my main board with a 40 pin
ribbon cable (I only need UART and a couple of TTLs), but the display is
currently powered from jumpers on this header. I hate to have multiple
connectors to a single header: asks for assembly trouble.
Is it OK to supply 5.25v to both microUSBs rather than feed-through?
Lacking schematics, I am not sure.

Again thanks for your help.
Graham.


#7

We sell this, which may be exactly what you need: https://shop.pimoroni.com/products/split-microb-usb-power-cable

Alternatively, I’ve had success powering from two separate AC adapters, but that gets a bit messy. A split connector and a good supply is the tidiest solution, and the one I use most of the time.


#8

Neat! it’s on the way. Have a great weekend. Graham.