This Lazy Old Geek (L.O.G.) loves Arduinos. I have noticed that a lot of sensors, like GPS, LCDs, magnetometers are 3.3Vdc sensors. But the standard Arduinos, Uno, RBBB are 5Vdc modules. So I decided I’m going to make more of my Arduino projects with 3.3Vdc AtMega328s. Now I’ve done this before but will go through some of the problems. PROBLEM: The standard Arduino uses a 16MHz crystal.

Now if you look at the documentation, the AtMega328P will operate from 1.8 to 5.5Vdc. However, the speed grades chart shows that the AtMega328P may not work with a 16MHz crystal at 3.3Vdc. (See chart) SOLUTION: So the preferred solution is to switch the crystal to 8MHz. So the easiest way (or so I thought) to start using an Arduino 8MHz 3.3V is with a protoboard. Well, I have this one setup to use a USB-BUB or in my case a USB-BUB substitute, PL2303.

The Arduino Duemilanove has a number of facilities for communicating with a computer, another Arduino, or other microcontrollers. The ATmega168 and ATmega328 provide UART TTL (5V) serial communication, which is available on digital pins 0 (RX) and 1 (TX). Arduino Uno to connect with serial 3.3v device. Ask Question. Up vote 1 down vote favorite. The hardware device that should speak with Uno, is need 3.3v to work, but the arduino Uno is output 5v. I was thinking that a resistors divider on the TX of the arduino would do the work, is that correct?

I made these with my USB Arduino Instructable: These can supply 3.3Vdc. PROBLEM: I tried about five different PL2303 modules and only one of them worked. So my first thought was that the PL2303 IC is supplying the 3.3Vdc and maybe it can’t supply enough current. I haven’t seen how much 3.3V current the IC supplies and it also powers itself. SOLUTION?: Well, I tried adding a 3.3Vdc regulator powered by 5Vdc to see if that fixed the problem.

Still didn’t work. I tried different crystals and different AtMega328 chips, still no luck. SOLUTION: Well, I remembered my friend OffTheRails2010 saying that the cylindrical quartz crystals (see picture) won’t work on a prototype board, though they work okay when soldered onto a PCB. I did some testing and found that the cylindrical crystals would work but the voltage had to be over 3.45Vdc on my particular setup. Well, the protoboard seems to work okay with a regular 8MHz crystal.

In most cases, I design my own Arduino circuits. The standard Arduinos with shield like the UNO and Duemilanove would be hard to convert to an Arduino 8MHz 3.3V. (I do believe I have an Arduino clone that can be switched to 3.3V by Seeedstudio). One really nice Arduino 8MHz 3.3V (no shield) is the Sparkfun Arduino Pro Mini 328 3.3V/8MHz: But for prototyping a good Arduino I like is an RBBB. So I decided to modify one: The RBBB kit comes with a 16MHz resonator.

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(I don’t remember but I think I bought RBBB blank PCBs and not kits). Anyway, I don’t like to use resonators so I used a 16MHz crystal and two 22pF capacitors. For my Arduino 8MHz 3.3V, I used an 8MHz watch crystal and two 22pF caps.

The second and third pictures show how I soldered the parts to one of my RBBBs. The RBBB can be powered by a 7-12V wall wart but as you might be able to tell, I haven’t soldered in a Pwr Jack or regulator. I could actually use a 3.3Vdc regulator but haven’t found the need to yet. Another way, the RBBB can receive power is with the six pin strip on the left side. The third pin from the bottom is labeled 5V and supplies power to the AtMega328. Okay, this six pin connector is designed to be used with the USB-BUB (See picture): This module converts a computer USB signal to the serial signal needed by the AtMega328.

It also supplies 5Vdc for the RBBB. Now this is pretty nice as you only have to have one USB-BUB but can use it on many different RBBBs. TIP: The Arduino UNO and other shield compatible Arduinos have this or similar circuits built in. ASIDE: The USB-BUB is a fine product and I do have one.