simple 10 sec power supply for max 5 minutes per day

Hi,

I have a simple question: I have my arduino uno rev 3 board and gy-30 sensor connected to a USB of my pc; Arduino has 2 works to do:

  1. send the value from 1*gy-30 sensor to my pc (already done & working)
  2. when pc turn off, wait 10 secs and then send gnd to the motherboard connector to restart it (simulate 1 sec pression of power btn) (already done the "on_state check" using another topic)

BUT
I have an issue: how can I power arduino without problems for this 10 secs without external psu/batteries or complex circuits?

If I put something like a super cap like this:

http://www.ebay.it/itm/SUPERCONDENSATORE-1F-5-5V-21x7-5mm-/290960040070?pt=Componenti_elettronici_passivi&hash=item43be91e086&_uhb=1

can it power my arduino for these 10 secs? In a day the pc could be stay powered off for a max of 5 minutes (divided in periods of max 10 secs, and I configured that the minimum time between power on and next shutdown will be near 200 secs, and obviously in this period USB will be powered).

I need something really cheap and simple... my electrotechnic knowledge is awful :~

Thanks!

On the motherboard you will find a jumper to switch power on to usb (even when pc is off) problem solved.

But yes a 1f cap should be ok providing it does not leak a couple in series and feed it a regulator to regulate the voltage... meanwhile the caps are tearing into the psu 5vs usb rail. (Use a couple of 60 ohm 1/2 watt or so do the calculation to charge the 1uf capacitor)

The dilema is the regulator uses mucho currento. You would have to do a custom setup or the caps will bleed dry from all the other ics drawing current.

Seems the simplest solution would be a cheap cell phone charger. That's assuming your PC is running from AC power which it appears to be since it is on all the time. If the PC goes off but the AC is ok your arduino will still have power and do its thing. If the PC goes off because the AC is off there is no use trying to restart the PC until the AC comes back on at which time the Arduino would also have power.
Either that or strap the PC to deliver USB power all the time as another poster suggested.

I like cjdelphi's first suggestion. The ATX power standard allows for always-on USB and one of the 5V rails never turns off to supply this. It's designated 5V Standby (or 5VSB) and on most wiring looms is the purple wire.

On the PC I'm typing on only the USB sockets cabled to the front of the case have power all the time, while the HP and Dell in the room appear to not deliver that 5VSB power through to any ports. It might be worth checking first what your PC can be setup to do as it could save you needing any additional power supply for this.

Cheers !
Geoff

Why do you need a regulator from a USB port? It seems people get used to seeing 7805s in every circuit, whether they're necessary or not. :wink:

USB -> Schottkey diode -> cap(s) -> AVR. It'll survive the couple hundred mV drop across the diode, you don't need 5.00v to power an AVR. The voltage will drop over time, until it hits the brownout limit set by the fuses. No biggie.

True, but 2 capacitors in series may exceed 5v if already charged? I'm thinking of 2 say 16v caps, this would not be an issue if they were say 2.5v each...

I'm just concerned about the caps potentially rising voltage and blowing the micro hence a regulator but he's better off with a zener to ap the voltage.

Um, why are there caps in series again? With one cap (or multiple paralleled caps), they'll only charge to the voltage input from the USB port.

RoyK:
Seems the simplest solution would be a cheap cell phone charger. That’s assuming your PC is running from AC power which it appears to be since it is on all the time. If the PC goes off but the AC is ok your arduino will still have power and do its thing. If the PC goes off because the AC is off there is no use trying to restart the PC until the AC comes back on at which time the Arduino would also have power.
Either that or strap the PC to deliver USB power all the time as another poster suggested.

Thanks RoyK and all people that helps me!,
yes, finally i used this solution: I didn’t used it before because i didn’t know that I can use usb & external psu contemporary; so now i solved this issue; now i’m searching a solution for finding if pc is on or off, and how to simulate the pressure of the botton to power on motherboard;

I thought to check power state using the led power on pin of the motherboard (ehm… the pc is totally disassembled and i don’t need the standard pc led) connected to a digital input of Arduino, and use another digital pin of arduino connected to power pin button to turn on the pc…

is it a good solution? can you help a poor noob in his project? :slight_smile: thanks

You can use the power led to signal computer on.

I used bluetooth and an arduino to do exactly what you're doing, remember to put in a fail safe of long button press to force power off if the pc fails to shutdown.

I thought to check power state using the led power on pin of the motherboard (ehm… the pc is totally disassembled and i don’t need the standard pc led) connected to a digital input of Arduino, and use another digital pin of arduino connected to power pin button to turn on the pc…

That will work. I would use opto-isolators between the arduino and PC but I’m admittedly a bit paranoid about things like that.

You don't need optoisolaters.

hell, you're using the computers own usb power supply! ...

(Hello brick wall, how are you today?)

RoyK:

I thought to check power state using the led power on pin of the motherboard (ehm... the pc is totally disassembled and i don't need the standard pc led) connected to a digital input of Arduino, and use another digital pin of arduino connected to power pin button to turn on the pc...

That will work. I would use opto-isolators between the arduino and PC but I'm admittedly a bit paranoid about things like that.

the power when the pc is off will come from external PSU, so i'll think in the future to sometring similar

ok, I'm thinking about something like:

int readpin=10 //the led pin connector to check if pc is powered on
int writepin=11 // the pin connected to pwbtn
int var;
void setup {
pinmode(readpin, INPUT)
pinmode(writepin, OUTPUT)
}
void loop {
var=digitalread(readpin)
if(var==0){
  delay(10000)
  digitalwrite(writepin, #whatvalue?!?!?!#)
  ...and so?

}
}

now I need to know how to send for 0.5 or 1 sec gnd signal to writepin... I'm googling but if someone has the answer please write me :slight_smile:

Thanks!

digitalWrite(pin,HIGH);
delay(1500); 
digitalWrite(pin,LOW);

I'm getting the feeling he can't see my posts anyway lol he's ignored everything i typed so i guess i'll give up.

cjdelphi:

digitalWrite(pin,HIGH);

delay(1500);
digitalWrite(pin,LOW);




I'm getting the feeling he can't see my posts anyway lol he's ignored everything i typed so i guess i'll give up.

I'm not ignoring your posts: in your previous post you said that the power to arduino comes from the usb, but for me the fastest way was to plug an external power supply (i fought that doing this was dangerous for arduino, but now i know that it's not true), so the power isn't from the same psu of pc.

So, i know that the power btn of pc works putting ground on the power pin of motherboard when i press it: if i put:

digitalWrite(pin,HIGH);
delay(1500); 
digitalWrite(pin,LOW);

I send to the mobo 5v for 1500 ms and then i send ground, isn't it?

So i think I need the opposite thing, right?

You might be better off finding one of those ATX motherboard power cable extenders and hacking it to split off the +5vsb and power-on leads. That would make this whole thing a lot easier...