Manage the 5V or 3.3V output power supply

Projects Programming
1

Hello!

I am working on a battery-powered project with an Arduino UNO.

I got external components (MP3 player board, MonoAmp Breakout, 8 ? Speaker:, ..) that get power from the 5V and 3.3V output of my Arduino UNO. I would like to be able to stop suppling power to these external components when I send the Arduino UNO to sleep.

Is there any function (like the digitalWrite(xx,LOW) function for the pins) to power down the 5V or 3.3V output of my Arduino board ?

The external components powered by these outputs keep sucking on it, consuming most of my battery when my Arduino board is on a sleeping mode :frowning:

Thank you for your repliaes on that question or any other complementary solutions!

Luc

2

Use 2 relays - one for 5v and one for 3v3.

The code will look like this:

......
digitalWrite(relay_5v_pin, LOW);
digitalWrite(relay_3v3_pin, LOW);
.......

and to turn it back on do:

.....
digitalWrite(relay_5v_pin, HIGH);
digitalWrite(relay_3v3_pin, HIGH);
......
3

I got external components (MP3 player board, MonoAmp Breakout, 8 ? Speaker:, ..) that get power from the 5V and 3.3V output of my Arduino UNO. I would like to be able to stop suppling power to these external components when I send the Arduino UNO to sleep.

Stop using the Arduino 3.3 V output.
Use a small relay (or solid state switch) to control +5Volts to external devices... Derive the 3.3 Volt after the relay for +5.

The Arduino +5 must always be available (non-switched.)

Use a digital output with proper driver and flyback diode to control the relay coil. Turn off the relay before sleeping. Turn on the relay after waking.

You best understand issues associated with peripheral power-up: time to stabilize, buffer garbage, POR, etc.

Ray

4

Thanks sonic656 and mrburnette for your quick reply!

Ok, I'll buy a relay!

it's too bad that the +5v cannot be shutdown from the microcontroller :confused:

5

it's too bad that the +5v cannot be shutdown from the microcontroller :confused:

No. It's a good thing. There ARE ways, using relays and transistors, to add your own switch, downstream of the 5V pin, that you can turn on and off.

6

Hello again!

I have made some researches to buy a relay but I've discovered that a relay have a typical power consumption around 70 mA which is still to much for my battery-powered project :frowning:

While sleeping my arduino board has a power consumption around 35 mA.

The relay will consume twice as much as my arduino :confused: right ?

thanks for your replies :slight_smile: !

7

The relay will consume twice as much as my arduino :confused: right ?

Yes. A transistor, on the other hand, will use far less current.

8

truntz:
Hello again!

I have made some researches to buy a relay but I've discovered that a relay have a typical power consumption around 70 mA which is still to much for my battery-powered project :frowning:

While sleeping my arduino board has a power consumption around 35 mA.

The relay will consume twice as much as my arduino :confused: right ?

thanks for your replies :slight_smile: !

http://www.newark.com/nte-electronics/r40-11d2-12c/relay-dpdt-2amp-12vdc-sensitive/dp/02H7335

OMRON ELECTRONIC COMPONENTS

SIGNAL RELAY, DPDT, 12VDC, 2A, THD

SIGNAL RELAY, DPDT, 12VDC, 2A, THD; Coil Type:DC; Contact Configuration:DPDT; Contact Current Max:2A; Contact Voltage AC Nom:125V; Contact Voltage DC Nom:30V; Coil Voltage VDC Nom:12V; Coil Current:15mA; Coil Resistance:800ohm ;RoHS Compliant: Yes

The coil is 12 Volts but you can use a FET or transistor (with appropriate base resistor) to cycle the relay. The 12 Volts can easily be the V+ from which you derive +5 and +3.3 regulated. My experience is that a voltage of 9V will likely be fine for the coil but testing would need to confirm same.

Latching relays can often be found on eBay or from surplus providers. One can also make their own solid state version.http://www.allaboutcircuits.com/vol_4/chpt_5/5.html

9

Use a P-channel MOSFET for a high-side power switch.
Use next to no current to turn it on (pull it low).
Make sure to take any control signals low before removing power so the devices aren't powered via leakage current thru the control lines.

10

May I add that if the guy doesn't need to provide much current to his circuit he can tunr the 5V or 3.3V off by using a digital pin as GND?

I mean, the MOSFET or a transistor are a good way to turn something ON/OFF, but if you can stay within the current limits of the Atmega328 he can use one of the pins to sink the current and by turning such pin HIGH he can actually stop current flow.

I wouldn't use a relay if the circuit I need to drive operates at logic level voltages and I wouldn't add a transistor if I can use the internal Atmega328 transistors....

Make sure though you can stay within the pin limits (40mA) and you not exceed the total package current limit (200mA) for your board (those values are for a Uno R3 board).

11

doesn't need to provide much current to his circuit he can tunr the 5V or 3.3V off by using a digital pin as GND?

Op "could" sink from the 5V but not the 3.3V because when the CMOS output swung HI, the Adruino would attempt to source. A diode would prevent this but also limit the LO side to around 0.8 to 1.2 Volts because of the CMOS+ diode Voltage drops. Just a bad design.

I wouldn't use a relay if the circuit I need to drive operates at logic level voltages and I wouldn't add a transistor if I can use the internal Atmega328 transistors....

But, I would...
Because in addition to the sink offset voltage I already talked about, peripheral modules often have as much as 10uF of bulk capacitance which creates a current spike in the uC. Again, poor design. Also, sinking or sourcing external modules from data pins is a great way to take out the uC if something shorts or pulls more current than rated. Many design guides even suggest 100-470 Ohm series resistors for CMOS data-data connections.

Bottom line, the uC is not a power switch: it is a binary data switch.

Ray

12

Ok mrburnette, I take your points

13

If power is a concern, stop using an Uno, that 30ma is almost exclusively used by the USB->serial circuitry. Get an Arduino Pro without all the USB stuff and use an FTDI to program and you'll get down to ua usage when asleep

14

Thanks all of you for your great replies!

I'll take all of them into account to move on on my project.

Thanks again!