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Grand Central M4 Board Power Consumption?
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Grand Central M4 Board Power Consumption?

by Ada485 on Fri Feb 01, 2019 2:53 am

I checked for technical literature but was unable to locate any that speaks about the maximum current draw the Grand Central M4 might have @ 12VDC when being powered only through the 2.1mm barrel connector. Looking to ensure a high enough amperage rating power supply is being used. Presumably it cannot pull more than 500 mA at 5 VDC through the USB port but that seems possibly a bit low if everything is running on the Grand Central M4? That's still 2.5 watts though, which is not nothing for a chipset like this.

Edit: I did just come across this information here. https://learn.adafruit.com/adafruit-gra ... al/pinouts

The MicroUSB jack provides 5V at 500mA or so, there is a fuse that will shut off temporarily when more than 1000mA is drawn, this is to protect a computer USB port. You can plug this into any computer or USB charger with a USB cable. You can draw up to 500mA between the Vin, 5V and 3.3V supplies (combined).

The DC Jack is a 5.5mm/2.1mm center-positive DC connector, which is the most common available. Provide about 6V-12V here to power the Metro. There is no fuse on this connection so you can draw more current, up to 800mA between the 5V and 3.3V supplies, and 2A from Vin.


So that sort of answers this? So presumably toss on a 1A 12V power supply and maybe a 0.8A fuse as well?

Are there any downsides to powering this at 12VDC in terms of overheating or other issues? I know some of the older Arduino boards would work at the higher end of the voltages but they were not happy about it either and it reduced some of the things you could do so you had to keep that in mind. Does the Grand Central M4 care about if the incoming power is 6V or 12V? Locating 6V power supplies is a bit harder to do than 12V.

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Re: Grand Central M4 Board Power Consumption?

by adafruit_support_mike on Sat Feb 02, 2019 7:26 am

The actual upper limit is around 200mA, and that's a worst-case value for the SAMD51.

The current consumption for a 32-bit microcontroller varies with the number of peripherals that are active and their clock speeds, but I'd say 50mA would be a reasonable upper limit in most cases.

Using a 12V supply will waste energy, since the microcontroller and most of the other devices operate at 3.3V. About 60% of the power will be burned off through the voltage regulator.

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Re: Grand Central M4 Board Power Consumption?

by Ada485 on Sun Feb 03, 2019 4:11 am

We figured a good bit would be just wasted as heat but the lower end is such an odd voltage for the world of industrial power supplies. Most of them are 12V, some 5V but 5V would not power the Arduino since it needs 6V minimum, even though it is a 3.3V board?

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Re: Grand Central M4 Board Power Consumption?

by adafruit_support_mike on Sun Feb 03, 2019 4:44 am

You can connect a 5V supply to the 5V pin. That's tied to the onboard 5V regulator's output.

It would be a good idea to make the connection through a diode, so the actual voltage reaching the 5V pin is about 4.3V. That's more than enough for the onboard 3.3V regulator, and will eliminate the chance of a power supply conflict if you plug in a USB cable.

There's a power-source selection circuit that opens and closes the connection to 5V-USB, but it works by comparing half of the voltage at Vin to the 3.3V rail. Volltages higher than 6.6V on Vin disconnect 5V-USB from the general 5V rail, but that doesn't help when you supply power through the 5V pin.

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Re: Grand Central M4 Board Power Consumption?

by Ada485 on Sun Feb 03, 2019 12:22 pm

Thank you. That is really helpful. Is this documented somewhere? I assumed you could do VIN power feeding but was unclear how well that played with USB power or if there were limitations if you started using higher current on multiple ports.

Probably a 1N400x diode or such? Looks like doing this is unregulated but we would be using an industrial well regulated power supply to begin with. Need to check the Grand Central schematics.

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Re: Grand Central M4 Board Power Consumption?

by adafruit_support_mike on Mon Feb 04, 2019 4:52 am

The power selection circuit is part of the Arduino Reference Design, I've just read that schematic enough times to know it offhand.

A 1N4001 would be fine, and you could probably use a 1N4148. If you have a well-regulated 5V supply to feed in, that just makes life easier.

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Re: Grand Central M4 Board Power Consumption?

by Ada485 on Fri Mar 08, 2019 5:59 pm

What's the maximum current the Grand Central could be fed with then by an outside regulated 5V supply? 2A? We have an application that needs a good number of 15 mA SSR units to be activated, which adds up. Could use an I2C breakout board if needed but trying to see how many pins + base current + other busses we can use here without going ppast the hardware limits.

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Re: Grand Central M4 Board Power Consumption?

by adafruit_support_mike on Sat Mar 09, 2019 1:36 am

This section of the tutorial talks about the available power connections and current limits:

https://learn.adafruit.com/adafruit-gra ... ctions-2-3

To hit the high points, you can get a combined total of 500mA from the Vin, 5V, and 3.3V pins when you power the Grand Central from its USB jack. You can get 2A from Vin and a combined total of 800mA from the 5V and 3.3V pins if you plug DC supply between 6V and 12V into the barrel jack.

The amximum current per GPIO pin is complicated.. most pins will fail if you send more than 8mA through them, but some will fail at 2mA. You also have to deal with 'clusters' of pins that get their power from the same internal supply, and the total current for each supply. For that, you'll need to look at section 6.2.9 of the SAMD51 datasheet.

Generally speaking, the SAMD51 is built for smarts, not for power. If you have anything that uses significant power, it's best to use a power distribution network outside the Grand Central. The 5V and 3.3V pins are good for a few external devices like sensors, but not for serious power.

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Re: Grand Central M4 Board Power Consumption?

by Ada485 on Sat Mar 09, 2019 2:00 am

Interesting. So the 40 mA on a MEGA output pin is now closer to 8 or even just 2 mA on the 3.3V Grand Central. Is that also the case with the DUE?

https://www.arduino.cc/en/Hacking/PinMappingSAM3X
Sort of but some pins can support 15 mA without issue. You just have to be careful which ones.

We want to drive some SSR relays. They only need 15 mA to activate and since they are SSR there is no coil inrush but it sounds like we cannot activate any of them here directly on the Grand Central?

There are I2C and other breakout boards that we could use of course but I guess we assumed we could drive a dozen or so of these directly from the Grand Central. Is that not really the case then?

Is there a map somewhere of what pins can draw a certain amount? Right now not sure where that information is other than buried somewhere in the datasheet.

Given it takes about 2 months right now for the Grand Central to get back in stock, would prefer not to destroy one during development.

You can get 2A from Vin and a combined total of 800mA from the 5V and 3.3V pins if you plug DC supply between 6V and 12V into the barrel jack.


Just to clarify then, if we feed it regulated power in over Vin and respect the 15 mA limits for outputs, what kind of total current can we expect to be able to use on the Grand Central? 2000 mA? Does the 800 mA add to the 2000 mA from the Vin?

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Re: Grand Central M4 Board Power Consumption?

by adafruit_support_mike on Sat Mar 09, 2019 5:13 am

Ada485 wrote:Interesting. So the 40 mA on a MEGA output pin is now closer to 8 or even just 2 mA on the 3.3V Grand Central. Is that also the case with the DUE?

It's probably somewhere around there. 32-bit microcontrollers are made for smarts and speed, not for power.

Ada485 wrote:https://www.arduino.cc/en/Hacking/PinMappingSAM3X
Sort of but some pins can support 15 mA without issue. You just have to be careful which ones.

That's the SAMD-3-x series of microcontrollers. There's no reason to assume those limits apply to the SAMD21 or the SAMD51, and the datasheets are full of reasons to assume they don't.

You can try if you want, but it will be entirely at your own risk. We won't replace boards killed by current levels above the absolute max specified in the datasheet.

Ada485 wrote:We want to drive some SSR relays. They only need 15 mA to activate and since they are SSR there is no coil inrush but it sounds like we cannot activate any of them here directly on the Grand Central?

That's correct. You'll want to use line drivers like the 74x245, which are specifically designed for higher output current.

Ada485 wrote:There are I2C and other breakout boards that we could use of course but I guess we assumed we could drive a dozen or so of these directly from the Grand Central. Is that not really the case then?

Negated query syntax is always tricky: the real case is 'the Grand Central's pins can not drive 15mA devices directly.'

Ada485 wrote:Is there a map somewhere of what pins can draw a certain amount? Right now not sure where that information is other than buried somewhere in the datasheet.

We don't have a diagram, but the pin clusters are listed in section 6.2.9.

Ada485 wrote:Given it takes about 2 months right now for the Grand Central to get back in stock, would prefer not to destroy one during development.

That's understandable.. I wouldn't want to destruction-test one even if they were always in stock.

Ada485 wrote:Just to clarify then, if we feed it regulated power in over Vin and respect the 15 mA limits for outputs,

You'll kill the board.

The 8mA/2mA limits aren't subject to any negotiation I can do. If you can convince a representative from Microchip/Atmel to say 15mA is okay, I'll take their word for it, but will wait for somebody else to test it on their own hardware first.

Until then I'm going to be as monotonous as gravity, for mostly the same reasons.

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Re: Grand Central M4 Board Power Consumption?

by Ada485 on Sat Mar 09, 2019 6:11 pm

adafruit_support_mike wrote:It's probably somewhere around there.


Sort of but not quite? See previous link for a much more readable version. The Due seems like it is quite comfortable outputting 15 mA for a SSR across quite a few pins. Technically about 50 of them.

That's the SAMD-3-x series of microcontrollers. There's no reason to assume those limits apply to the SAMD21 or the SAMD51, and the datasheets are full of reasons to assume they don't.


I agree, that's for the SAMD3X series and not the Grand Central's chip. More interesting to note the differences is all, given they are both 3.3V native boards. That's why we are trying to locate the pinout list and determine what each pin is actually rated for. May have to dig it out of the datasheet if nobody has put it together yet. Want to make sure we set this up correctly is all since we thought we could use 15 mA relays directly. Will move it to a I2C relay output board or theoretically to the Due though those are max current and we would prefer to stay below that in operation.

Due Pin Number | SAM3X Pin Name Mapped Pin Name | Max Output Current (mA) | Max Current Sink (mA)
0 PA8 RX0 3 6
1 PA9 TX0 15 9
2 PB25 Digital Pin 2 3 6
3 PC28 Digital Pin 3 15 9
4 both PA29 and PC26 Digital Pin 4 15 9
5 PC25 Digital Pin 5 15 9
6 PC24 Digital Pin 6 15 9
7 PC23 Digital Pin 7 15 9
8 PC22 Digital Pin 8 15 9
9 PC21 Digital Pin 9 15 9
10 PA28 and PC29 Digital Pin 10 15 9
11 PD7 Digital Pin 11 15 9
12 PD8 Digital Pin 12 15 9
13 PB27 Digital Pin 13 / Amber LED "L" 3 6
14 PD4 TX3 15 9
15 PD5 RX3 15 9
16 PA13 TX2 3 6
17 PA12 RX2 3 6
18 PA11 TX1 3 6
19 PA10 RX1 3 6
20 PB12 SDA 3 6
21 PB13 SCL 3 6
22 PB26 Digital Pin 22 3 6
23 PA14 Digital Pin 23 15 9
24 PA15 Digital Pin 24 15 9
25 PD0 Digital Pin 25 15 9
26 PD1 Digital pin 26 15 9
27 PD2 Digital Pin 27 15 9
28 PD3 Digital Pin 28 15 9
29 PD6 Digital Pin 29 15 9
30 PD9 Digital Pin 30 15 9
31 PA7 Digital Pin 31 15 9
32 PD10 Digital Pin 32 15 9
33 PC1 Digital Pin 33 15 9
34 PC2 Digital Pin 34 15 9
35 PC3 Digital Pin 35 15 9
36 PC4 Digital Pin 36 15 9
37 PC5 Digital Pin 37 15 9
38 PC6 Digital Pin 38 15 9
39 PC7 Digital Pin 39 15 9
40 PC8 Digital Pin 40 15 9
41 PC9 Digital Pin 41 15 9
42 PA19 Digital Pin 42 15 9
43 PA20 Digital Pin 43 3 6
44 PC19 Digital Pin 44 15 9
45 PC18 Digital Pin 45 15 9
46 PC17 Digital Pin 46 15 9
47 PC16 Digital Pin 47 15 9
48 PC15 Digital Pin 48 15 9
49 PC14 Digital Pin 49 15 9
50 PC13 Digital Pin 50 15 9
51 PC12 Digital Pin 51 15 9
52 PB21 Digital Pin 52 3 6
53 PB14 Digital Pin 53 15 9
54 PA16 Analog In 0 3 6
55 PA24 Analog In 1 3 6
56 PA23 Analog In 2 3 6
57 PA22 Analog In 3 3 6
58 PA6 Analog In 4 3 6
59 PA4 Analog In 5 3 6
60 PA3 Analog In 6 3 6
61 PA2 Analog In 7 3 6
62 PB17 Analog In 8 3 6
63 PB18 Analog In 9 3 6
64 PB19 Analog In 10 3 6
65 PB20 Analog In 11 3 6
66 PB15 DAC0 3 6
67 PB16 DAC1 3 6
68 PA1 CANRX 3 6
69 PA0 CANTX 15 9
70 PA17 SDA1 3 6
71 PA18 SCL2 15 972 PC30 LED "RX" 15 9
73 PA21 LED "TX" 3 6
74 PA25 (MISO) 15 9
75 PA26 (MOSI) 15 9
76 PA27 (SCLK) 15 9
77 PA28 (NPCS0) 15 9
78 PB23 (unconnected) 15 9
USB PB11 ID 15 9
USB PB10 VBOF 15 9

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