DIY Breadboard Friendly ATTiny85

Let me start by stating that I have no formal knowledge of electronics! This works, but if I've broken some cardinal rule of electronics, let me know and I'll update the design.

The modularity of Arduinos is great, but after playing with them for a year or so, I wanted to start building things that needed a little more integration. I also wanted to design the components and programming around the actual controller I'd be using. So, I decided to start by building a small breadboard friendly ATTiny85.

A project I've been thinking about will require interfacing with a Bosch BMP280 pressure sensor and controlling a standard servo. So I decided to power the Tiny85 with a 3.3 volt regulator so I wouldn't have to do any level translation between it and the BMP280, and also add a 5 volt regulator to power the servo. The 3.3 volt regulator can supply 80 mA, which should be more than enough for the Tiny85, the BMP280 and a few other odds and ends. The 5V regulator can supply 250 mA which should be plenty for the micro servo I intend to use, which I measured at around 80 mA under typical operation. Once I have everything working on the breadboard, I can simply extend the circut to integrate the pressure sensor and other components and cut a new PC board.

I added a small status LED just to indicate that the board was receiving power, but this could easily be omitted. Outside that, it just consists of a few smoothing capacitors and a resistor to pull up the reset pin on the Tiny85.

The capacitor and resistor values were chosen based on data sheet schematics and those I've seen used in other Tiny85 based boards, as I assume they know what they're doing far more than I do!

As I said, I don't know much about electronics, and my admitedly too-short attempt to learn Eagle sent me running to what I already know - Adobe Illustrator! Not an appropriate circuit design application by any stretch of the imagination, but like my little microcontroller itself, all I can say is... it works!

As they say, a picture is worth a thousand words, so instead of boaring everyone to death, I just documented the steps with photographs.

If you have any questions or comments, feel free to e-mail me.

  Parts list:

5 Volt Regulator
3.3 Volt Regulator
SMD 1.5 and 10k resistors
SMD 1uf and 22uf capacitors
Misc building supplies (PC board, solder, CNC milling machine, etc.)

DXF Outlines

This is the circuit I designed. On the top of the board (left) the I/O pins are on the right and on the left, from top to
bottom, are: 5V out, VIN, Ground, 3.3V out and Reset. On the bottom (right) there's the two voltage regulators, two
smoothing capacitors (one on the voltage input, one on the 3.3V output, and a pull-up resistor for the reset pin.
I couldn't fit the smoothing capacitor for the 5V out on the bottom, so I put it on top, along with the status LED and
it's limiting resistor. Again, this all works... but if anything isn't technically correct, feel free to let me know.

Once the circuit was laid out, I combined all the paths and shapes into contiguous outlines.

Tool paths generated from my CAM program. I have a CNC mill, and it's a lot less messy to just mill PC board than etch it.

Top circuit milled, using a .017 inch end mill... that snapped shortly after this!

Bottom circuit milled and board cut out.

Finished board, removed and cleaned up with a little fine sand paper.

Circuit board hanging out in a bottle of liquid tin for a few minutes.

Tinned board and all the components to add.

Solder paste added for the bottom components using the tip of an Xacto knife... the pins on that 3.3 volt regulator are tiny!

Bottom components added and ready for some hot air. I broke down and bought a hot air rework station, soldering surface
mount components this small with an iron is a bit tedious and frustrating. I've done it, and don't need to do it any more!

Bottom components soldered.

Solder paste added for top components.

Top components soldered.

Pins placed and soldered. Since the through-holes aren't plated, I had to make sure the bottom circuits were
soldered to the pins as well to ensure the top and bottom circuits were connected.

Finished board, from the bottom.

Finished board, from the top.

Board placed in a breadboard and wired up to an Arduino Nano for power and programming.

Board running a simple test program, reading the state of the button and turning the LED on/off. It works!

Hope everyone likes it. Again, if I did anything wrong or if the circuit could be improved, let me know and I'll update it for the next one.


Chris O'Riley
306 Briarwood Ct.
New Paltz, NY 12561
tel (845) 256-8934

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