A tiny, barebones Arduino for interfacing with 3.3V sensors

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This project uses the ever famous ATMEGA328P, and breaks out a few digital outputs and the I2C and SPI lines. It clocks in at approximately an inch square and is suitable for embedding into tight spaces. This board uses a resonator of 8Mhz and a voltage level of 3.3V. It has power, I2C data and user leds. I2C and SPI are broken out along with some other GPIO.

The next step is to add a USB interface with a CP2102N UART to USB bridge

I built this project so that I could interface with 3.3V sensors/radios easily because few Arduino Pro Mini clones are 3.3V or have a small form factor.

The costs are about $6 per board, the major cost factors being OSHPark ($2.30) and the ATMEGA328P ($2). Other significant components are the resonator and reset button, coming in at around $1.50.

Full Schematics and layout have been uploaded!


d10 is the LED

x-eagle-schematic - 188.83 kB - 03/27/2018 at 13:23


x-eagle-board - 86.09 kB - 03/27/2018 at 13:23


  • Part 1/3 complete

    Ben Lim03/27/2018 at 13:27 0 comments

    Whoops! Forgot to add in the schematic and layout files! The next step is to add in a CP2102N chip so that it has onboard USB! How cool will that be?

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Makerfabs wrote 01/20/2018 at 03:36 point

as my estimation, the production cost should be half of your cost....$3 totally :)

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Ben Lim wrote 01/20/2018 at 13:58 point

This is a tiny run so the cost is high per board. If there is a way to keep the overall cost low as well as reduce the price per board, I would love to hear the breakdown! :D

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david wrote 01/20/2018 at 02:20 point

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andrey.malyshenko wrote 01/19/2018 at 19:34 point

Why not 2mm pitch? Would save even more space probably

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Ben Lim wrote 01/20/2018 at 13:56 point

Connectors for the 2mm pitch are not common, so I opted for the more common 0.1" standard.

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Lee Cook wrote 01/19/2018 at 12:32 point

You could reduce the cost of this a lot.  Get around 160 boards for $11 from jlcpcb with shipping, change the resonator to a cheaper crystal and (given they're likely just reset switches without a huge amount of usage) source your switches from ebay:

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Ben Lim wrote 01/20/2018 at 14:05 point

I agree for the boards! However they take a while to ship and the shipping costs outweigh usually double the price.

I wanted to keep the component count low, and SMDs, so I opted for a resonator instead.

Thanks for the link on the switches! That will certainly drop the cost by a lot!

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Vishnu Mohanan wrote 01/18/2018 at 15:43 point

Why do you need an external resonator when you have an 8 MHz RC oscillator inside of ATmega328 ? I recently converted an Arduino Nano clone for full 1.8 to 5V operation with internal oscillator. Is the resonator more stable than RC oscillator ? Hope so..

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Ben Lim wrote 01/19/2018 at 01:13 point

Typically resonators are more stable than internal oscillators. I believe this is true for the ATMEGA328P as well.

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Vishnu Mohanan wrote 01/19/2018 at 05:41 point

Do you have a datasheet of the resonator you're using ? I've never used the kind you're using.

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Ted Yapo wrote 01/18/2018 at 13:56 point

Nice!  Which regulator are you using, and do you know if it comes in a 3.0V version?  I have similar needs, but for 3V devices.

  Are you sure? yes | no

Ben Lim wrote 01/19/2018 at 01:15 point

3.3 or 3V? I was using a 3V battery so I didn't need a regulator. I think the SPX3819 is a suitable regulator, it comes as an adjustable as well as 3V and 3.3V regulator. If you want USB -> Serial, the CP2102N has an internal 3.3V regulator that can supply up to 100mA!

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