1 of 1 people found this helpful
Purely looking at the photo of the product I can deduce:
- It connects via HDMI for visuals
- It powers up the Raspberry Pi via the GPIO pins from the controller board of the touch screen
Going from the datasheet I can deduce:
- Touch controls are either via USB or via i2c on the GPIO
- It may include a USB power cable from the controller board of the touch screen to the Raspberry Pi
Thus, you power the Raspberry Pi either from the controller board, or you can power the Raspberry Pi separately.
If you want more details, get in touch with online support.
I agree with your first set of deductions.
Touch via USB - yes, there is a micro-USB to USB cable included which I assume is for that purpose. There's also a 5-pin cable which I assume is for using I2C instead, but there's nowhere on the display board to connect that cable (that I can see, anyway!)
Power via USB - it doesn't include a cable for this; the supplied USB cable wouldn't do it (micro-USB at the Pi end would mean there'd need to be a USB-A connector at the display end, and there isn't).
Powering the display itself is my biggest problem: there isn't a recommended PSU, and the dimensions and polarity of the power connector aren't documented. Polarity I can probably guess as that's fairly standard, but dimensions aren't; the 12v PSU I had to hand (from a USB drive caddy) which I tried didn't power the display, and it's not clear whether that's because the inner pin wasn't making contact, or the polarity was wrong, or something else.
I'll contact online support and see if they have any more info; if I succeed I'll report back here for the benefit of anyone else looking, but in the meantime if anyone has this display working I'd love to find out what PSU they're using.
3 of 3 people found this helpful
There is this note on the Farnell web site:
I've just installed one on a Pi3B+. There was a USB lead which I took from the display's board to the Pi which supplies the Pi's power. There is a solid double ended U shaped HDMI connector to connect the two devices (hence it won't easily fit a Pi4 without some serious mucking about) and then a red and blue lead to connect to pins 2 & 3 (or if it is longer pins 1 & 3) of the Pi's GPIO pins. Finally you need a 12 volt supply to the device (not the Pi). The Pi then takes its power from the USB. I used a 500 mA 12V psu but it wasn't quite up to it so then put a 1A supply in.
I expect you've seen this, but if not, it might be just about enough to get going.
It really should come with better instructions.
The customer Q&A note on the website is mostly correct.
Here's what I've worked out so far:
- I got myself a 2A universal PSU, which allowed me to set 12v and came with a range of connectors to test. 3.4mm outer diameter worked for me; there were two of such supplied with different inner dimensions, and it was the one with the smaller inner dimension which fitted, but I don't have anything to measure it. Positive is on the inner, negative on the outer.
- There are no visible signs on the board if it is powered, although the screen's backlight should come on if there is a live HDMI connection.
- The power to the Pi comes from a connector on the board (not USB - that's for the touch screen interface). The board has a 6-pin connector, the supplied cable is 4-pin. It needs to be installed pin 1 to pin 1 (to the left hand end of the connector, not centrally, despite that it looks like it should line up centrally). That might sound obvious but (at least to my eyes) it wasn't obviously a 6-pin connector due to the shape of the connector's enclosure, and if you think it's a 4-pin connector it doesn't work!
- Power is to GPIO pins 2&6 (red to pin 2). These are the 1st and 3rd pins on the RHS of the GPIO connector (hence the incorrect "pins 1&3" reader comment I assume). The reader comment implies that some screens are supplied with a 2-pin GPIO connection, in which case use 4&6 (2nd & 3rd on RHS of connector). Google "Pi GPIO pinout" for more info.
- Start with a fresh Raspian image before you test something you already have; in my case, an existing image didn't work but a new image did (not yet worked out what setting might be breaking it). (Side note: by default, the Pi doesn't enable the HDMI output unless connected to a screen when powered up.)
- Note that Raspbian doesn't come with a virtual keyboard out of the box so you'll need a keyboard plugged in too. The touchscreen did, however, work out of the box.
- There is an I2C cable supplied but nowhere obvious to connect it on the board. I don't need this, but my best deduction so far is that the touchscreen is I2C and connects to the board which has a I2C to USB conversion on it. Ergo if you want to use I2C directly then you need to disconnect the existing I2C cable from the screen to the board and connect the Pi's I2C connection directly to the screen. Remember that is untested speculation and I can't tell you the correct pins for that on the Pi GPIO, sorry.
- You don't have to power the Pi from the screen if you don't want to. Just don't connect the power cable to the Pi if so. Which also means you can use it without mounting a Pi onto the back of the screen.
Given that this is sold as a Pi upgrade, some more docs are needed, not just to formalise the above. What do I need to install on the Pi to get a virtual keyboard, for example - a touchscreen without one is a bit useless.
I'd add that the image quality and touchscreen accuracy all seem pretty good and well worth the money. A sheet of A4 with some instructions, or a link on the website, would make this a great piece of kit.
> I got myself a 2A universal PSU
If I understand what I read correctly, there's 500mA for the screen, and then you need extra for the Raspberry Pi, and the 3 B+ advises on about 2.5A
> What do I need to install on the Pi to get a virtual keyboard, for example - a touchscreen without one is a bit useless.
You have the options of what's available in linux really, for example:
sudo apt install matchbox-keyboard
And then it's in
Accessories -> Keyboard
From the GUI.
I'm not entirely familiar with the packages, but there may be some official one from Raspberry Pi or other suitable software.
> If I understand what I read correctly, there's 500mA for the screen, and then you need extra for the Raspberry Pi, and the 3 B+ advises on about 2.5A
3A would have been better but I picked something I could get the same day. 2A is adequate for running a Pi but it depends what else you plan to hang off the back of it. For my application the Pi will be separately powered anyway so it wasn't a concern, but I should have said so in my comments.
> sudo apt install matchbox-keyboard
Funnily enough I've spent the day trying to get this to work, but I think that's my code not the keyboard. (Specifically: I need it to auto-popup when needed, which seems to be how it should work once running, but isn't how it's working for me.
I've just taken delivery of one of these:
.. but it comes with no instructions.
Looking at the customer Q&A I'm not the only one finding this issue.
The docs say it needs a 12v 0.5A supply plus whatever the Pi needs (so, realistically, a 12v 3A supply?) but doesn't state the power connector polarity or dimensions.
The most helpful (albeit only) customer answer suggests that the display supplies power via USB but that doesn't sound right - I assume the red-black cable connects to the display on the 4-pin connector and to the Pi's GPIO header to supply power. There is another cable which I assume to be the "I2C Touch Interface Cable" referred to in the docs but if there's anywhere to connect it to the display board I can't see it! (The supplied USB cable is more obvious.)