Rewiring an Arduino Clone for 3V3

The Arduino platform is very useful; it would be more useful if it ran at 3.3V. Fortunately it's really easy to modify an Arduino to achieve this using only one additional component: a SOT223 regulator such as an AMS1117-3.3. The following instructions cover modification of an Arduino Nano clone to run at 3.3V, with annotation where the instructions differ for genuine models.

1.

De-solder the VUSB input diode and the 5V regulator. The diode connects the USB 5V bus to the Arduino supply rail. The regulator does nothing if the device is powered from USB. Rather, it only provides power if the Arduino is being powered from a >5V source on its VIN pin. Removing the diode will entirely disconnect the Arduino from the USB 5V bus. What we're doing to the regulator is more complicated, on which more later.

Arduino clones are not standardized so pay attention to the part marking on the regulator. If it's not an AMS1117 or the part marking has been removed, you'll want to read the board traces. If pin 3 is not connected to VIN then bear that in mind for following steps.

These parts can be removed with a soldering iron provided you're willing to resort to violence. A hot air gun is preferred.

2.

Solder your replacement AMS1117-3.3 regulator to the open footprint left by the removed 5V regulator. If the old regulator did not have a standard pinout, you'll have to use a different replacement 3V3 regulator or perform some dead-bug soldering.

3.

Solder a bodge wire between the VUSB pad of the removed diode and the VIN pin of the replaced regulator. If your regulator had a nonstandard pinout then ignore the following image; solder the wire to whichever pin is tied to VIN.

4.

Solder a second bodge wire between the VCC pad of the removed diode and pin 4 of the CH340G USB-UART converter chip. The CH340G has an onboard 3V3 regulator on pin 4, which is where the 3V3 pin is normally supplied from in 5V operation. Now that we're running the entire board on 3V3 we'll have to short that pin to the supply rail per the CH340G datasheet.

Pay attention to the part marking on your Arduino clone's USB-UART converter chip. If it's not marked then it's almost certainly a CH340G. However, play it safe and check the board traces to confirm that the IC's pin 4 is routed to the Arduino's 3V3 pin. If not then your board isn't using a CH340G and you'll have to do your own research by identifying the chip and reading its datasheet to see what it requires for 3V3 operation. Alternatively, take a small risk and identify whichever device pin connects to the 3V3 Arduino pin. Use that pin instead of pin 4 as above.

If you're using a genuine Arduino your board will have an FTDI IC or a standalone Atmel microcontroller. Both of these will have onboard 3V3 regulators that will need to be rewired in similar but different ways for overall 3V3 operation. It shouldn't be difficult to read the datasheets for the respective chips to figure out which device pins need to be rewired and how to rewire them.

5.

You're done. The Arduino should program as normal. However, VIN is now tied permanently to the 5V USB bus and cannot be powered if the device is also plugged into USB. Don't make that mistake, you might fry your PC's USB driver. If you need this functionality (I don't) then you can solder the removed diode in series with the VUSB-VIN bodge wire.