I Guys
I'm trying to put up a project and i have a couple of doubts here, maybe someone can help me..
I've got a atx psu setup, and i intend to use the 5vsb to power the arduino only, and the 12v a couple of step motors, i want to be able to switch on the psu when i want, until here everything is almost ok.
The problem lies in that, i need the usb connection always on, i know i can cut the power from the usb cable, but i really dont like that solution, therefore, i still need the usb connection at the same time i get power from the 5vsb.
The thing is that i really dont want to connect to the 5v pin, and i was wondering if i could just use something like this LM2577-DC-DC-Step-up-Power-Module-Adjustable-Voltage-Power-Converter-Module to boost the 5vsb to say 9v and power the arduino from the jack and still use a regular usb connection?
Thanks in advance
This would work, but you'd need a way to switch on the PSU. I'd assume that you'd connect the control (green) pin of the ATX PSU to a pin and pull it LOW to turn it on and HIGH or high resistance to turn it off. Instead of using a step-up converter, why not use the PSU's 9V or 12V and feed it into the VIN? You don't need the converter and it's a bit more efficient. Have you considered:
- Your system needs to control the PSU from a signal from the USB. Probably set everything up, pull the green pin LOW, and display a message to (optionally) disconnect USB.
- Does it need to turn itself off? Just pull it HIGH or high resistance to turn itself off. However, it needs a USB connection again to start back up.
Other than that, your system works! When you power the arduino with more that 7V, it disables USB power and switches to external. I'd imagine code like:
const int controlPin=5;
void setup() {
//by default controlPin is high-resistance
Serial.begin(9600);
Serial.println("Do setup stuff");
Serial.println("All done, turning on PSU");
pinMode(controlPin,OUTPUT); //Pulls LOW
Serial.println("You may disconnect USB");
}
void loop() {
delay(2000);
Serial.println("Turning off (unless USB is connected)");
pinMode(controlPin,INPUT); //brings controlPin to high-resistance
}
Thank you for the reply.
The thing is my psu doesn't have 9v, only 5v and 12v..
Yes i'm using the green control wire to power on the psu when i need more power for the devices i'm controlling.
I can only use the 5vsb to power the arduino, i can't use no 12v or 5v from the psu because it needs to be off until i send a signal to the psu to be on and give the 12v and 5v to the devices.
I only need to power the arduino and a couple of buttons and leds from the 5vsb.
Since i don't want to use the arduino 5v nor Vin, i was thinking on boosting the 5vsb power to 9v so i can use the arduino power jack (it will be regulated again to 5v by the arduino) and still be able to maintain a regular usb cable connection at the same time without further modifications.
One other question would lets say those boosted (my atx gives 5v 2A on the 5svb rail) 5v-9v with 1a(after this voltage boost i should lose 1A here) be able to power 2 arduinos ?
ptv1p3r:
One other question would lets say those boosted (my atx gives 5v 2A on the 5svb rail) 5v-9v with 1a(after this voltage boost i should lose 1A here) be able to power 2 arduinos ?
You shouldn't loose 50% of your power: that'd be 5W of heat from the converter. The converter that I found is http://www.ebay.ca/itm/LM2577-DC-DC-Step-up-Power-Module-Adjustable-Voltage-Power-Converter-Module-/261096788682?rmvSB=true, and it shows that it has a ~92% efficiency. So, if you used it to convert 5V into 9V, you would loose 8% of power to heat, giving you 1.84A, not 1A. 1.84A is definitely enough to do two arduinos: remember, each arduino, when on USB, can only use 0.5A at max.
Also, if you have wires coming from the converter, why not just feed it into VIN? The barrel jack and VIN are connected to the same place.
Thank you for the reply 
"1.84A, not 1A. 1.84A" you are very correct sir, thank you, i didn't catch correctly the efficiency percentage, and that LM2577 is exactly the one i ordered