USB password generator PCB

The most popular project of all time at Code and Life has been my DIY USB password generator. When I made it, I used a piece of veroboard that just fit inside a USB memory stick enclosure. Well, guess what: Benjamin Lunt just recently designed a custom PCB for it! I’ve been exchanging e-mails with him (Ben has written a book on USB, another very popular topic also in my blog) and he was kind enough to ship me one of these neat boards. Here’s what it looked like:

In addition to a nice USB connector footprint, this design also has a green power LED and a red transmission LED (which needs a small firmware change). Once assembled, the thing is really tiny, and it does work great. Thanks a lot for Mr. Lunt for designing this one! Be sure to visit his blog, as he’s interested if anyone would also like to have one (I know I did :). Maybe he’ll even publish the design files if someone wants to tinker with it (of course making your own isn’t too hard either).

On the right you can see what mine looked after some soldering (click for a larger image) – I love the fact that small resistors from Partco all had different base color for different values… I had to compromise a bit and use 48 ohm resistors instead of 58, and 4k7 instead of 2k2. For the LEDs, I used 480 ohms.

Olimex and ATtiny2313 breadboard header

This is the final article in my ATtiny2313 breadboard header series. In the previous parts we’ve looked at:

In this part, I’ll have a short review of the PCB ordering process with Olimex, and a bit how the boards turned out. Let’s get going!
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DipTrace and PCB manufacture with Olimex

It’s time to wrap up my DipTrace tutorial series with a brief look at how to do Design Rule Check (DRC) with the PCB layout tool, and generate gerber files for board manufacture. Take a look at the previous part on how the board was done.

I chose Olimex PCB prototype service because it’s very inexpensive by itself: 30€ for a two-side 160x100mm euroboard plus 5.50€ for shipping. They also can panel your designs and I counted that 16 ATtiny2313 headers would fit into a single board while still leaving room to cut them apart. Read on what was needed to make sure my PCB design was ready for manufacturing!

Design Rule Check (DRC)

The first thing before ordering was to investigate Olimex requirements for the boards. I knew I had no overlapping drill holes and had taken care to use only drill sizes supported by them (35 and 39 mils), so the most important ones for me were:

  1. At least 8 mils spacing between tracks/pads
  2. At least 8 mils for pads (i.e. 16 mils larger pad than drill hole)
  3. Less than 20 % of area without solder mask
  4. Over 500 drill holes costs a bit extra

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PCB design with DipTrace

Continuing from part 1 of this ATtiny2313 breadboard header with DipTrace -tutorial, I’ll now go through the PCB design. In DipTrace Schematic Editor, I used File->Convert to PCB (CTRL-B) to get the components and connections exported to PCB Layout tool. Like it’s schematic counterpart, also this tool is quite easy to use.

First I change the grid to 5 mil so each step is half of the 10 mil breadboard hole spacing. I then proceed arrange the components roughly to final layout, and add two 10-pin headers which will plug into breadboard. I then remove some component names which are not sorely needed, and change the location for the remaining ones to the center of the component.


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ATtiny2313 Breadboard Header with DipTrace

Sooner or later there comes a point in your electronics career where it would be nice to have a schematic for the project you are doing. If you have a steady hand and lots of paper to spare, the first option is to draw the schematics on paper. However, computer aided design (CAD) software does have it’s advantages, allowing easy modifications, sharing and later PCB creation.

In this short tutorial, I’ll show how to create a simple schematic using DipTrace, an excellent electronics CAD package that has a free version as well as inexpensive entry-level commercial and non-profit licenses. The circuit I’m doing is a simple ATtiny2313 breadboard header that integrates an ISP programming header, a few capacitors, a reset pullup resistor and a clock crystal, eliminating the need to wire these things every time I start a new project. Additionally, I’m showing how to use DipTrace’s powerful facilities to create new components in literally few minutes. Let’s get started!

Why DipTrace and not Eagle CAD (or some other brand)?

The electronics CAD software, the most often recommended software for beginners is Eagle CAD. The main reasons are probably the rather reasonable pricing and large existing userbase. Also, a lot of open hardware projects share their schematics in Eagle format, and many PCB fabrication shops accept Eagle files directly without conversion to Gerber format.
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