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Is it possible to power the Grand Central with 5V....but not
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Is it possible to power the Grand Central with 5V....but not

by gradybooch on Wed Jun 12, 2019 3:57 pm

Adafruit documentation for the marvelous, wonderful, absolutely incredible Grand Central (yes, I like this board!) states (https://learn.adafruit.com/adafruit-gra ... al/pinouts) that

There are two primary ways to power the Grand Central:

-- Through the Micro USB port up at the top left
-- Through the DC jack at the bottom left

and goes on to observe that with the DC jack one should

Provide about 6V-12V here to power the Metro.

Is there a way to power the Grand Central with 5V NOT using the Micro USB port?

I'm using the M4 in the context of some outboard electronics that will draw about 1.5A at 5V, which means that I can't pull this through the board. Therefore, I've devised a power distribution circuit for that bit, but I hate to need a dual voltage power supply to bring 6-12v to the DC jack.

My questions are thus

-- can I power the Grand Central via the DC jack with 5v?
-- if not, is there a way I could safely bring 5v into the board other than the two primary ways listed in the aforemetioned pinout documentation?

I suppose I could stuff it in via the USB port, but I'd prefer to leave that port unused for when I need to attach this device to another computer, rather than using it just for power.

Thanks!

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Re: Is it possible to power the Grand Central with 5V....but

by fasteddy516 on Thu Jun 20, 2019 10:49 pm

I had a similar requirement on a project with a Grand Central and a Meanwell LRS-75-5 14A power supply that was supposed to be the common supply for everything in the system. I ended up "customizing" a USB cable by stripping off an inch of the outer jacket and isolating the 5V wire (the red wire in every USB cable I've ever seen). I clipped the red wire, insulated the part of it that comes from the host, and connected the 5V from the Meanwell supply to the part that heads into the Grand Central. This allowed me to power the Grand Central from the Meanwell supply and still connect it to my laptop for programming/etc.

It's not the most elegant of solutions, but it seemed like the best way to avoid offending the power circuitry (and bypassing the built-in protections) on the Grand Central and still get the connectivity I needed.

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Re: Is it possible to power the Grand Central with 5V....but

by gradybooch on Fri Jun 21, 2019 1:52 am

Excellent hack!

In end end, I settled on a simple power distribution that routes 9v to the M4 and also a 9v to 5v 5A converter.

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Re: Is it possible to power the Grand Central with 5V....but

by jjarosz on Wed Aug 28, 2019 9:05 am

The Grand Central has a VIN pin on the Power Header (lower left hand header). Have you look into using that?

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Re: Is it possible to power the Grand Central with 5V....but

by adafruit_support_mike on Sun Sep 01, 2019 7:03 pm

You can also connect a 5V power source to the 5V pin on the GPIO header.

Vin is connected to the input of the 5V regulator, which needs a couple volts of headroom. The 5V regulator's output is connected to the 5V pin and to the input of the 3.3V regulator. The 3.3V regulator powers the SAMD51 and most of the rest of the board.

So as long as you connect the 5V pin to enough voltage to run the 3.3V regulator, the Grand Central should run happily.

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Re: Is it possible to power the Grand Central with 5V....but

by evgbrowns on Sun Mar 22, 2020 10:22 pm

I have a new Grand Central that says its having power problems at times. It is connected via USB to a Raspberry Pi 4. With nothing connected to any I/O, it was working fine off USB power. I connected a MOSFET driver and solenoid to a digital out pin and I kept getting a message that said power unexpectedly dipped and it was in safe mode when I went in and out of REPL. It also wouldn't run the code.py file at power up. I rummaged in my junk pile of orphaned power supplies and found one labeled 7.5V/1000ma supply with the right connector and hooked it up. Things seemed to work fine then (the solenoid didn't, another story). I disconnected the MOSFET and started working on RP to GCM4 communication via UART. I turned on UART5 on the RP and connected GCM4 0 to RP 12 and GCM4 1 to RP 13. I was able to send data from the RP to the GCM4 fine, but was getting the power dipped messages again. I disconnected the UART cross connect and no longer had the power dipped messages. I have had the RP screen output go blank a couple times when the cross connect is in place, and a couple times at (RP) boot. I checked the GCM4 VIN pin and I actually see 10.7V. I occasionally get a popup on the RP saying a removable disk was removed without being properly dismounted, referring to the CIRCUITPY drive. This isn't consistent, at the moment the cross connect is working fine with no power dipped messages. The RP is on a dedicated 3.5A USB supply. Any thoughts on what's going on here would be greatly appreciated.

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Re: Is it possible to power the Grand Central with 5V....but

by adafruit_support_bill on Mon Mar 23, 2020 5:00 am

Please post some photos or a wring diagram showing how you have everything connected.

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Re: Is it possible to power the Grand Central with 5V....but

by evgbrowns on Mon Mar 23, 2020 11:23 pm

GCM4 with RP.JPG
Full setup
GCM4 with RP.JPG (234.17 KiB) Viewed 85 times
Here's the setup. Of course, being watched, its behaving today, though I did get a couple soft reboots on the GCM4 when I was copying files off it to the RP.

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Re: Is it possible to power the Grand Central with 5V....but

by evgbrowns on Mon Mar 23, 2020 11:23 pm

GCM4.JPG
GCM4 showing connections to RX/TX
GCM4.JPG (220.61 KiB) Viewed 85 times

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Re: Is it possible to power the Grand Central with 5V....but

by evgbrowns on Mon Mar 23, 2020 11:25 pm

RP.JPG
RP with 12/13 connected to GCM4 plus a stepper driver and reed switch
RP.JPG (206.68 KiB) Viewed 85 times

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Re: Is it possible to power the Grand Central with 5V....but

by adafruit_support_bill on Tue Mar 24, 2020 5:56 am

I don't see a common ground in your photos. Connect a ground wire between the boards. You need a common ground reference since this is what the signals are measured against.

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Re: Is it possible to power the Grand Central with 5V....but

by evgbrowns on Tue Mar 24, 2020 10:07 am

OK - I thought the USB connection between the two provided that, but I can easily make that additional connection. Thanks for your help.

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Re: Is it possible to power the Grand Central with 5V....but

by adafruit_support_bill on Tue Mar 24, 2020 10:18 am

Not sure about the Pi. But USB ports are often isolated, so the USB ground reference is only useful for the USB signals themselves.

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Please be positive and constructive with your questions and comments.