Suitable USB cable powering Pi3 and 7" Touch LCD [SOLVED]

[elkberry]

I'm struggling with hassle-free powering a Raspberry Pi Model 3 together with the official 7" touch LCD, avoiding the yellow flash of insufficient power supply in the display during operation.

My Raspberry Pi Model 3 has two USB devices attached: an Edimax WLAN dongle, as well as a Logotech universal receiver. Yes, I need a second WLAN in addition to the built-in.

1. Attempt: original 2.5A USB power supply, connected to the LCD touch. Using a short USB cable then from the display to the Raspberry Pi 3. The result: especially during boot the yellow flash is showing most of the time.

I've tried several different USB cables between the LCD and Raspberry Pi, but to no avail. Again, the yellow flash is with too many a time.

2. Attempt: 5A USB supply, with 2 short USB cables wiring up LCD and Raspberry Pi separately. This works quite satisfactorily. Unless I hotplug USB devices, but that sems to be a well known problem, so a powered hub is thr cure. However, the cabling is cumbersome, as the only reliable way I've found so far is using very short USB cables, around 10cm each.

So, is it even possible to wire the power supply in sequence, first the LCD, then the Raspberry Pi? What cables do I need and where can I get "heavy gauge" USB cables that actually work in this scenario?

Or is this the wrong wiring anyway? Reading through the official documents seem to suggest that this should work. Anyway, where can I get good USB power cables, as these seem to be the really crucial component here...?

[alphanumeric]

This may or may not help you but here goes. I have a Solderless breadboard setup I use to play around with breakout boards and other electronics etc. It's a Pi 3B with the Pi foundation 7 inch touch screen attached. A ribbon cable goes from the GPIO bus to a breakout board plugged into a solderless bread board. I use a 5V 10A (overkill I know) power supply that has a barrel jack power plug. From that I feed my display and Pi separately with custom USB power cables. I also made up custom USB cables for any devices connected to the Pi. From the Pi's USB ports only the Data + and - and GRD are wired up. On the device end power comes from my 5v power pack, not from the Pi. No rainbow low voltage warnings ever.
I used connectors like this https://www.adafruit.com/products/1387 and this https://www.adafruit.com/products/1390

[GordonTGopher]

Don't know whereabouts you live, so this may not be viable, but try https://thepihut.com/collections/raspbe ... pi-display

Gordon

[elkberry]

alphanumeric, this is an interesting alternative you are pointing out, thank you for this idea: I wasn't aware of USB micro plugs either for DIY soldering, or with barrel jack socket. I've followed the link and searched the site. Unfortunately, they don't have any ready-made heavy gauge cables on sale.

[elkberry]

Gordon, thank you very much for this link, I tried to google such a suitable cable but somehow missed that source. Ordering should be no problem, more so before the Brxt.

Is the cable you link to much better than ordinary short adapter cables? I'm asking because I've tried with one of the usual short cables, powering the LCD from the original RasPi 2.5A power supply. That triggered a lot of flashes, so I rather doubt that the original 2.5A supply is suitable for RadPi3+LCD?

Edit: I've ordered the aforementioned LCD-RasPi cables and will test them when they arrive. PiHut describes them as having heavier wires because they've thrown out the data cables. We'll see...

[alphanumeric]

Something like this will work, https://www.adafruit.com/products/3068 with the do it yourself connectors. Just get a roll of the black too. Or if your feeling lucky, cut the end of off a cable(s) you already have. Strip the ends bare and tin the ends with a soldering iron. I used one of these, https://www.adafruit.com/products/368 with this https://www.adafruit.com/products/658 Then just ran the wires to what I wanted to power to the two screw terminals. I have plans to replace it with this, https://www.adafruit.com/products/610 and solder the wires instead of using the screw terminals.
Pictures on my breadboard rig can be seen here in my Public OneDrive folder, if your interested. https://1drv.ms/f/s!AjOYwiwlwDtpgq9LUHdGiiRpn7dr2Q It's been revised, redone, updated several times.

[alphanumeric]

I have one of those Pi-Hut cables, 2 actually, ordered them a while back but never used them. Every time I come by them in my box of Pi stuff I think "I should try one of those" but just haven't bothered. My display card on my Pi display has a cover over it, and is not easy to get at. I can't see the connectors at all. It's the bottom part of a Pi PIBOW case, with my Pi in an identical case mounted on top of with stand offs. Then an open beam frame around that. tight courters. It's a fair bit of work, and some disassembly just to get at it. It's working just fine so I leave well enough alone.

[elkberry]

As I intend to use my LCD-RasPis for demonstration purposes, I'm using the open frames from Pimoroni (in different colours, of course). This way, people can clearly see the RasPis, as well as the LCD adaptor board below. Access to the USB connectors is still possible, as is swapping micro SD cards; I'm using different ready-made boot mSDs for different scenarios/setups.

On a side note, screen recording on the RasPi3 itself works, so I can record raw LCD screen footage, and later edit them for use within tutorial videos.

[alphanumeric]

Mine is a semi portable setup. It's an open beam frame with 4 very short stubby legs in the 4 corners. A large solderless bread board front and center with the display tilted back at 33 degrees right behind it. I take it out on my deck in the summer and put it on a table under my gazebo. Then fire up my laptop beside it. I have a few small modifications planed for it this summer so I will likely put one of those PiHut cables in to simplify things. I may actually use both, one feeding the display board and one from it to my Pi. Then mate the one feeding power to the display board to something like this, https://www.adafruit.com/products/2225 Those cables are bit to short I think to cut the plug off and tin the wires etc.

[elkberry]

Finally, my (very) short LCD-RasPi USB power cables from the PiHut arrived.

So the verdict is out: these cables work perfectly, no more under-voltage flash bolts.

The cable is almost too short, you need to plug it in before you mount the Raspberry on the backside of the 7" Touch display. On the plus side: this cable won't ever wiggle loose. If you plan to protect the Raspberry Pi on the backside using a Pimoroni Pibow coupé, then you need to leave out the bottom plate (0), as the cable lacks a few milimeters.

LCD-Raspberry Pi USB power cable from the PiHut

raspberry pi lcd short power cable pihut small.jpeg (52.16 KiB) Viewed 5795 times

[alphanumeric]

That cable would never work for my setup. I have a Pibow Midnight Limited Edition case on mine. And the bottom plate from another of the same case used as a cover for the display driver board. With standoffs in between. I have two sets of standoffs between my Pi and the display driver board. Pictures here, if you want to take a look, https://1drv.ms/f/s!AjOYwiwlwDtpgq9LUHdGiiRpn7dr2Q The last half dozen or so deal with the display and Pibow covers.

[elkberry]

I've now had the chance to test also the Pimoroni twin USB cable (see below, also shown is PiHut's LCD short cable to the left).

LCD-RasPi power cables

tmp_15592-lcd cables173345631.jpeg (57.63 KiB) Viewed 5678 times

Both cables are successfully powering both the Raspberry Pi 3 B as well as the official 7" Touch Display from the same 2.5A official power supply. No yellow bolt to be seen, no flashing red power LED.

The twin cable has plugs that are longer than that of the official power supply. They still fit with the Pimoroni LCD frames, but it's a close shave.

Twin cable

tmp_15592-twin cable-1520972722.jpeg (59.75 KiB) Viewed 5678 times

[DaveCooper]

I had exactly the same problem as the OP, also with 7" touchscreen, B+ pi, wifi dongle and (in my case) AB Electronics io expansion board. After a look on this forum I decided not to use usb connectors at all. Instead I'm using an embedded switch mode power supply from XP Power rated 3A at 5V. I've connected it up using molex kk connectors, powering to the 5 way connector on the touchscreen pcb and (via the AB part) the gpio power pins on the Rpi. The power supply has a very good overcurrent protection on the output, so I'm happy to rely on that rather than the polyfuse on the pi.

Since using the new power supply the performance has been totally flawless. Before it was very shaky: booted successfully ~50% of the time, lots of yellow lightning icon.

Here's the set up, in an old machine case: power in is via the filtered iec inlet in the foreground left, 5V connectors to the pcbs are white.

Dave Cooper

(XP unit is ECL15US05-S. I should say I'm not here to advertise XP's products, just passing on something that worked really well for me)

[elkberry]

What I find interesting is the connectors you use. They look much better than the fiddly jumper connector cables that comes with the LCD.

[DaveCooper]

Hi Elkberry,
I'm afraid I tried those jumper leads just once and binned them. The connectors in the pic are 1/4" crimp fastons on the mains connector (which has 1/4" spade ends), the xpower psu has screw clanp terminals, and the connectors on the pcb are 0.1" pitch molex kk crimp connectors. The kks require a crimp tool, which is a bit painful. I think I paid about £20 for a crimp tool from ebay. I've had it at least 10 years, so although the initial cost was a bit steep (tho' dirt cheap by crimp tool standards!) it's been a really good investment.
Dave

[KanoMaster22]

I know this is an old post but I use a 1m long USB cable to connect the Pi and the Touchscreen with no problems!