Under-powering the Arduino

[Saimaster13]

The Arduino has a 5V regulator to get 5V to the Arduino, but reading the Atmel chip's datasheet, it seems to suggest that the power going to the Arduino could be anywhere from around 2 to 5 volts. Is this true? And are there any foreseeable problems by doing this (other than not being able to communicate or use electronics that require 5V)?

What I would want to do is put the Arduino chip on a PCB board and run it along with some LEDs and a RTC off of a 3-3.3V battery.




p.s. In case you wanted to see something that I am working on, I have made a board with 8 RGB LEDs on it to experiment with programming and designs. A video of it scrolling binary data (the amount of seconds the Arduino has been on for, or millis()/1000) can be found here. Reds are 0s and blues are 1s. I have also made an octal clock (not scrolling) out of it since then, but haven't shot a video of it yet.

[bitfogav]

You are correct the atmel device can run 2v-5v (1.8v - 5.5v) but like you have pointed out, connecting a lower power to devices that require a min 5v can lead to issues.

The issue is that the pins on a 5v device will require a certain threshold to read as a logic 1 which is usually between 2-3volt on TTL devices but this maybe more (depending on the device). and also RTC's disable comms at certain voltages.

If you are just running an atmel with leds and a low power RTC then I cant see any problems running at a lower power, but you might have to consider the oscillator speed

clockvspower.jpg (9.42 KiB) Viewed 15022 times

You could also use the Sleep function to put the atmel to sleep when not needed, this will save on power consumption.
Maybe Brad might have some other advice on this as I think Brads Christmas 8x8 matrix project ran on a low power system.

[Chuckt]

The Arduino has a 5V regulator to get 5V to the Arduino, but reading the Atmel chip's datasheet, it seems to suggest that the power going to the Arduino could be anywhere from around 2 to 5 volts. Is this true? And are there any foreseeable problems by doing this (other than not being able to communicate or use electronics that require 5V)?

What I would want to do is put the Arduino chip on a PCB board and run it along with some LEDs and a RTC off of a 3-3.3V battery.

I have seen a tutorial on how to do this:

http://www.ladyada.net/library/arduino/3v3_arduino.html

I can't offer much more help than this.

[Saimaster13]

That's easier than I thought. Any suggestions or foreseeable problems are welcome. I am using a 3.3V RTC unit and LEDs, so there shouldn't be any problems with the lower voltage on the other devices.

[brad]

Some good information there guys!

The PIC chip in the PICnDuino runs at 3.3V and interfaces just fine with standard TTL logic circuits. however some devices (like LCD displays) still require a 5 volt power supply to run, even though their logic inputs will recognise logic 1's down at the 3.3v level.

[Saimaster13]

Alright, I'm going to go ahead and try it, it definitely should work.

[Chuckt]

That's easier than I thought. Any suggestions or foreseeable problems are welcome. I am using a 3.3V RTC unit and LEDs, so there shouldn't be any problems with the lower voltage on the other devices.

My only suggestion is keep it on a constant power supply but if it is from battery power, low voltage may make the clock slow down or operate in the unsafe voltage area (see Bitfogav's graph above) in the graph above. If it doesn't behave normally, you should carefully check the DC voltage with a multimeter. As a battery is drained, low voltage may occur so maybe a 3.3 or 3.7 benchtop power supply or a wall power supply will work with the voltage regulator dropping it down to the necessary voltage.

[brad]

That's right Chuck, if you don't have a regulator in there then as the battery drains, your power supply voltage will go down.