FlyingBirdy
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Power Supply

Sat Nov 23, 2013 8:11 am

What is the reason, that the Power Supply section is unassembled (than it would be great).

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Gert van Loo
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Re: Power Supply

Sat Nov 23, 2013 8:24 am

I spend a lot of time on that supply but had to drop it in the end.
The Pi has no reverse diode on it's USB 5V input. Thus if you plug a supply on the Gertduino and forget to unplug the regular 5V supply, the Gertduino can start back-feeding the supply in the wall socket. That can get hot, catch fire with potential your house following.
Originally I thought that putting in big 70 point font in the manual a warning about NOT PLUGGING IN BOTH supplies would be sufficient but the lawyers decided it was not.
Just too risky.

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meltwater
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Re: Power Supply

Sat Nov 23, 2013 3:59 pm

Pesky Lawyers!
If only there was something we could put in that space... :D

Keep thinking up excellent things to do with the board...great stuff.
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shuckle
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Re: Power Supply

Sat Nov 23, 2013 4:16 pm

I do not undestand how it works. Where do you feed the power? Both rpi and gertduino needs separate 5 v input?

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Gert van Loo
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Re: Power Supply

Sat Nov 23, 2013 5:54 pm

The Gertduino and the Pi all feed from the same 5V supply.
The picture below is a simplified diagram of what happens if you use TWO power supplies.
(The real diagram is more complex and involves internal resistance of the supplies)
Thus the stronger supply starts to 'back-feed' into the weaker supply.
That energy has to go somewhere and it will heat up.
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shuckle
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Re: Power Supply

Sat Nov 23, 2013 7:09 pm

Clear, thanks.
It needs pretty good quality and strong power source then i guess.

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mahjongg
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Re: Power Supply

Sat Nov 23, 2013 8:42 pm

meltwater wrote: If only there was something we could put in that space... :D
Well, the gertduino comes with it's schematics, and they include the SMTP!
But if you assemble the SMTP and use it you are doing it at your own risk!

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meltwater
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Re: Power Supply

Sat Nov 23, 2013 9:33 pm

Somehow I think that space will be redesigned at some point. A hardware engineer with all that spare PCB space...
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Gert van Loo
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Re: Power Supply

Sat Nov 23, 2013 10:02 pm

It needs pretty good quality and strong power source then i guess.
It actually does not. The 328 will work from 2.7-5V and the Gertduino itself takes only a few tens of milli-amps.
It is when you start plugging in in power hungry shields when things can go wrong.

boyoh
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Re: Power Supply

Sat Nov 23, 2013 11:14 pm

I suggest if you are using different voltages
between your Pi and your breadboard
projects, you inter face using Opto isolators
This will give you total isolation, between
Different voltages, and protect you Pi
Inputs and outputs 3.3v & 5v
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mypifi
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Re: Power Supply

Sun Nov 24, 2013 5:33 pm

will we be able to buy the power supply bits to run the gertboard minus the pi?

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Gert van Loo
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Re: Power Supply

Sun Nov 24, 2013 7:14 pm

will we be able to buy the power supply bits to run the gertboard minus the pi?
They are generally available. After all I have to be able to build the prototypes. But if you mean: "will they come as a kit". I don't think so.

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mahjongg
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Re: Power Supply

Sun Nov 24, 2013 9:47 pm

boyoh wrote:I suggest if you are using different voltages
between your Pi and your breadboard
projects, you inter face using Opto isolators
This will give you total isolation, between
Different voltages, and protect you Pi
Inputs and outputs 3.3v & 5v
The PI and Gertduino are already using "different voltages", as the PI itself (the SoC) runs at 3V3, and the ATMega328 chip runs from 5V (to be compatible with all the Arduino shields), so there are level converters between the PI and ATMega chip, no optical isolators are needed for that. However in some cases an opto-isolator is a good thing to add, for example if you want to control heavy inductive loads like motors and power relays, but that is true for both PI's and Arduino/gertduino's.

boyoh
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Re: Power Supply

Sun Nov 24, 2013 10:48 pm

mahjongg wrote:
boyoh wrote:I suggest if you are using different voltages
between your Pi and your breadboard
projects, you inter face using Opto isolators
This will give you total isolation, between
Different voltages, and protect you Pi
Inputs and outputs 3.3v & 5v
The PI and Gertduino are already using "different voltages", as the PI itself (the SoC) runs at 3V3, and the ATMega328 chip runs from 5V (to be compatible with all the Arduino shields), so there are level converters between the PI and ATMega chip, no optical isolators are needed for that. However in some cases an opto-isolator is a good thing to add, for example if you want to control heavy inductive loads like motors and power relays, but that is true for both PI's and Arduino/gertduino's.
BoyOh ( Selby, North Yorkshire.UK)
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boyoh
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Re: Power Supply

Sun Nov 24, 2013 10:49 pm

boyoh wrote:
mahjongg wrote:
boyoh wrote:I suggest if you are using different voltages
between your Pi and your breadboard
projects, you inter face using Opto isolators
This will give you total isolation, between
Different voltages, and protect you Pi
Inputs and outputs 3.3v & 5v
The PI and Gertduino are already using "different voltages", as the PI itself (the SoC) runs at 3V3, and the ATMega328 chip runs from 5V (to be compatible with all the Arduino shields), so there are level converters between the PI and ATMega chip, no optical isolators are needed for that. However in some cases an opto-isolator is a good thing to add, for example if you want to control heavy inductive loads like motors and power relays, but that is true for both PI's and Arduino/gertduino's.
There is to much emphasis on buying ready made projects
Desining and building your own projects. Is more rewarding
Then if the project wont work. You will have a better idea
On how to test it.This might not involve using a Arduino,
So a Opto Isolator would be a lot cheaper.
There is a lot of good cheap surplus components on the market.
BoyOh
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plugwash
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Re: Power Supply

Mon Nov 25, 2013 1:17 am

Gert van Loo wrote: The Pi has no reverse diode on it's USB 5V input. Thus if you plug a supply on the Gertduino and forget to unplug the regular 5V supply, the Gertduino can start back-feeding the supply in the wall socket. That can get hot, catch fire with potential your house following.
If power supplies really caught fire when backfed then considering all the cheap USB hubs on the market with no backfeeding protection I think we would be hearing horror stories about it by now.
Gert van Loo wrote:The Gertduino and the Pi all feed from the same 5V supply.
The picture below is a simplified diagram of what happens if you use TWO power supplies.
(The real diagram is more complex and involves internal resistance of the supplies)
Thus the stronger supply starts to 'back-feed' into the weaker supply.
That energy has to go somewhere and it will heat up.
AIUI the majority of power supplies can only source current not sink it. So in most cases with a small load the supply with the slightly higher open circuit voltage will supply the load and the supply with the slightly lower open circuit voltage will supply no current (but won't usually draw any current either).

As the load gets heavier then it is likely both power supplies will start supplying current to the load.

Making a supply that can sink current as well as sourcing it requires more components, so it's unlikely to be seen outside specialist applications.

Dutch_Master
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Re: Power Supply

Tue Nov 26, 2013 3:54 am

The risk is actually that the weaker supply will start lowering it's voltage output as it sees the higher voltage on it's output. By doing so, more current will flow through the end-stage and that causes, as stated earlier, the overheating. Mind, there's no reason the GertDuino board couldn't have the protection diode on the port that connects to the RPi. Using a jumper the port can resume its normal function if the RPi is intended to be powered via the GD-board.

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jackokring
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Re: Power Supply

Wed Dec 04, 2013 12:43 pm

This looks like an interesting board. I guess there are a few questions.

1) Is the RTC/IRDA pre-programmed? As although it would be fun to do it later, there is enough to be getting along with making sketches for the 'duino.

2) Although the IRDA can't be on battery all the time, can it TX occasional remote control signals on battery? (Obvious for me but ...)

3) The connector is quite nice, but it does prevent stacking a small board under the 'duino. Any plans to make the long connector split?
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Gert van Loo
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Re: Power Supply

Wed Dec 04, 2013 1:13 pm

jackokring wrote:This looks like an interesting board. I guess there are a few questions.

1) Is the RTC/IRDA pre-programmed? As although it would be fun to do it later, there is enough to be getting along with making sketches for the 'duino.

2) Although the IRDA can't be on battery all the time, can it TX occasional remote control signals on battery? (Obvious for me but ...)

3) The connector is quite nice, but it does prevent stacking a small board under the 'duino. Any plans to make the long connector split?
1) All devices are empty, but Gordon Henderson has written code for both the RTC and the IRDA which is in the public domain.
So you don't have to re-invent it.

2) Sorry the IRDA chip is a receiver only.

3) I assume you mean the connector to the Raspberry-Pi. Yes, it is a major headache but I could not find a better solution.
You could, as you suggested, split it in two smaller stacked ones but that would be first more expensive and second less reliable.

rotwang
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Re: Power Supply

Sat Dec 07, 2013 1:22 pm

Simple solution -
1) split track from gertboard psu to respberry pi 5v pin, insert solder pads so competent user can bridge them. Assumption being that if you are competent enough to bridge these pads then you understand the consequences.

2) provide 2 pin header to take short lead ending in micro-usb connector to feed pi. This would be the place to insert an fet switch to power down the pi.

If there is to be a later version of the board, could I ask for a Mega2560 instead of a 328, I have some nice little projects which just won't fit into a 328.

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Tage
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Re: Power Supply

Sat Dec 07, 2013 4:01 pm

I would like to comment on the discussion regarding if a power supply can be damaged or overheated by back feeding it from another supply. (my background is in power supply design.)

It is definitely possible.

that is one reason why it is not a good idea to use powered USB hubs that do not meet the USB specification (the specification clearly states that the hub must not feed power into its upstream port under any situation).

most USB chargers of the type that plug into the wall socket are made as cheap as possible and they usually cannot sink current from another power supply that is connected to the same 5V output. but as the USB chargers are made for higher and higher power level and the requirements for low power dissipation becomes more important, the power supply gets more complicated and advanced.
Many power supplies now are able to sink current, even if it is only a small amount. power can flow backwards in the power stage and even if the current is small it must go somewhere. it can flow into the input capacitor and charge it up so an over voltage occurs which causes the power supply to fail. there is usually no detection of input overvoltage on such a small power supply, so the circuit continues to run with reverse current when the output voltage is forced above the setpoint - until it fails. the failure can cause a bang and smoke but normally not a fire. unless the design is low quality.

other than the risk of reverse power flow that can cause over voltage on the input side, there is a risk that the power supply can not handle a situation where the 5V output is held up by another supply when the input power is turned off. this happens in power supplies that are built for highest possible efficiency and have the output diode replaced by a MOSFET (synchronous rectifier). it is not uncommon that the designer of the power supply has not designed the circuit so that it can tolerate this situation. the risk is then that there will be very large current transients that overstress the components.

another dangerous situation is when the power supply already has 5V on the output when it starts. not all designs are made so the circuit behaves well in this situation.

with so many low quality power supplies from shady and unexperienced manufacturers coming on the internet market without having gone through the necessary design verification process and electrical safety tests, the risk of a failure (even a fire) caused by backfeeding is growing larger each day.

in the event of a failure there is a very real risk that the output from the power supply will all of a sudden be connected to the mains voltage because the insulation is damaged or the circuit board gets covered in soot or electrolyte from a capacitor.

questrov
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Re: Power Supply

Thu Dec 12, 2013 4:21 am

It actually does not. The 328 will work from 2.7-5V and the Gertduino itself takes only a few tens of milli-amps.
It is when you start plugging in in power hungry shields when things can go wrong.
So what is suggested if/when we do plug in (and stack) power hungry shields?

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Gert van Loo
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Re: Power Supply

Thu Dec 12, 2013 9:20 am

So what is suggested if/when we do plug in (and stack) power hungry shields?
You have to feed the whole system from a powerfull 5V supply connected to the 5V/GND on the Gertduino.

wjc52nc
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Re: Power Supply

Mon Nov 17, 2014 9:43 pm

I have read this whole sequence of posts and wondered how powering the whole system off of a powerful 5V supply on the Gertduino GPIOs was different than populating the Gertduino power supply as far as the potential for trouble due to multiple power supplies is concerned. I understand that, in both cases, the experienced user will know not to use two supplies.

That said and considering myself, if not an experienced user, at least one who takes responsibility for his own mistakes, I would like to populate the power supply on my beloved Gertduino. I completely realize that I could just use an Arduino but what I really want is the Vin supply to my relay shields and a single wall wart in my project and want to use the Pi. Is there a parts list (BOM) anywhere? I can obviously figure it out from the schematic but have already had some uncertainty about the barrel connector, for example. A parts list would save time.

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Gert van Loo
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Re: Power Supply

Tue Nov 18, 2014 6:58 pm

The difference is mostly there for the lawyers.

With supply I might be taken to court for any damages as a result from normal usage.

If you connect an external voltage, that is a modification and I am not responsible if user(s)
make modifications to the products.

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