ATX Power - Project and Downloads
Arduino vs independently powered hardware
Arduino is a board capable of working powered by several kind of voltages, including 5V non-regulated voltage.
A problem frequently emerging in forums is how to power external devices using Arduino and external power sources. Obviously, we should leave out all those cases where Arduino should work in a low-consumption, battery-operated environment (i.e. stand-alone self-operating machinery, robots and more). But lots of other cases exist when an external powering solution capable of covering a wide range of possibilities is needed.
In particular, I'm thinking in desktop machines, projects working with stepper and high-power DC motors but also indoor applications where Arduino controls visual applications, cameras, lights and projectors, electronic musical instruments etc. One of the problems is that it is difficult to have all the needed voltages and another is that it is not so simple to find a power supply with the needed current for all the cases.
What is a low-cost power supply universally adopted, that you can find with a wide range of currents, widespread in everyday activities? It's simple: It is the power supply of your desktop PC.
If you don't have in your garage stuff an unused case with 250W, 300W or more ATX Power Supply, you can buy one for less then 15,00-20,00€. At this price I found a 400W new ATX Power Supply bought as spare part from my electronics supplier.
This power suppliers cover several advantages:
- Efficient cooling system and voltages compatible with mainboards and computer peripherals
- Capable to supply high voltages
- All the model respect the same ATX12V specifications
- All-in-one in a small box
- Switching power supply
- Simple to find and cheaper then other circuits with the same characteristics.
What is missing?
If you try to power the ATX Power Supply to the mains and try to see what happens to the output connector... You will find only a GND and +5V. As a matter of fact, the switching ATX when is powered is in stand-by mode, just as it happens to the desktops. We need something similar to the PC power button to finally power our devices.
ATX Power 1.1 aims to work with every Switching Power Supply unit following ATX12V specifications giving to the devices of your project (and obviously to Arduino, too) the needed power sources: you have in the meantime GND, +3.3V, +5V and +12V capable to support 5A or more (it depends by the devices and the model of ATX Power Supply you adopted in your application).
The diagram is downloadable in pdf format.
To correctly power the ATX Power Supply (see the datasheet ATX12V specifications) I re-created the logic signal corresponding to the power-on button on the desktops, through the On/Off switch that changes the PS-ON Signal on the ATX connector between High to Low. To that aim, as you can see in the circuit, a NE555 device is used in Bi-Stable configuration.
The only power source always present on the output connector of the ATX Power Supply is SB (Standby) signal: this voltage is used to power the two leds - red for PowerOff and green for PowerOn -
The result is that if the power unit is off but it is connected to the mains, you will see the red light indicating that the system is in standby mode while the green light shows the system is powered.
ATX Power 1.1 Part List
Note: IC AT24CP can be one of the AT24Cxx series such as AT24C128B, AT24C1024 etc.
Part Value Device Package Library
LED1 Green LED3MM LED3MM led
LED2 Red LED3MM LED3MM led
R1 22K R-EU_0204/7 0204/7 rcl
R2 22K R-EU_0204/7 0204/7 rcl
R3 470 R-EU_0204/7 0204/7 rcl
R4 240 R-EU_0204/7 0204/7 rcl
R5 240 R-EU_0204/7 0204/7 rcl
S1 On/Off Switch A68-A31 A68-A31 switch
X1 Power AK300/4 AK300/4 con-ptr500
X2 5566-24 5566-24 5566-24 con-molex
Eagle board layout and electric diagram can be downloaded in zip format here.
I decided to "export" the ATX female connector to plug it without difficult to the ATX Power Supply, outside the power box switch.
The power side (output) of the circuit reports switched currents of +3.3V, +5V, +12V and GND signal.
When using this power unit only for several devices, in the same project remebmer to put all the circuit grounds toghether!
If you decide to fit all the circuit into a box, you can cut the PCB following the perimeter around the four holes. The power switch and the two LEDs can be inserted directly in the box cover, soldering them to the PCB using wires on the fly.
ATX Power 1.1 can also be bought. Read more in the Products area.
See the following images to have an idea of the final solution I adopted.
The power box with the holes.
The PCB with input and output screw terminals.
ATX cables connected to the power unit.
Finishing mounting and connections.
The power unit connected and powered.
Buy ATX-Power construction kit
You can buy the ATX-Power construction kit (excluded the container box) directly from this link.