Just thought to share a quick tip today. I’ve noticed that when doing work with AVR MCU’s, I’m using ATtiny2313, ATmega88 and ATtiny45/85 for 99 % of the time. I got tired of opening the Atmel data sheets every time when swapping a new chip into a breadboard, so I constructed a real cut’n’paste reference sheet by gluing the relevant portions on a piece of rigid cardboard:
I even used a piece of paper to mark the 6-pin header pinout, it’s a real time-saver! And thanks to the cardboard back, it’s easy to keep below my LCD monitor and pull out every time I need it. Additional idea would be to leave some white space around the pinouts and laminate it with clear contact paper, so I could doodle project-specific notes with a water-based marker and clean it after I don’t need them anymore!
Oh, and as you can see, I’m using a Mac this time to do some flashing. I installed the excellent Crosspack for Mac from Obdev guys. It’s a streamlined way to install avrdude and avr-gcc on a Mac, and now I can take my electronics hobby with me when I’m traveling. :)
One exciting piece of hardware I received with my Digikey order was an Arduino Uno board (R3). There was conflicting information whether or not it could be used as an ISP (in-system programmer), so I decided to see for myself. It turned out that with just one tweak, I could use the $26 device to program my AVR chips, essentially eliminating the need for a separate ISP such as $22 USBtiny!
This is obviously good news for any beginner with a budget, so I decided to write a short tutorial on how to do it. I used my USB password generator as a guinea pig for this project, so if you have wanted to try that out, this post also doubles as tutorial on how to build it on breadboard (good idea in any case before soldering it anywhere). Read on for details!
Until now, I’ve been ordering all my electronics supplies through the excellent Finnish firm Partco. However, after running out of ATtiny85 chips I just couldn’t make myself pay 5.90€ ($7.80) when the same part was available for third the price from Digi-Key. I decided to try the fabled distributor myself. In case you haven’t tried them yet, read on for my experiences.
Website and Shopping Process
It is surprising how such a successful electronics component retailer is able to operate with such a poorly laid out and difficult to use website. From a usability standpoint, it’s a prime example of how not do design a web store. There’s so much to critize it’s hard to know where to begin, but here my top annoyances for the front page alone:
I’m planning to make some RFID hacking in near future using 150 kHz tags. Since I don’t have a signal generator, I decided to go where quite many people have gone before and build myself one, more specifically a DDS. Instead of just taking a complete project from the net, I thought this would be a good way to learn a bit of AVR assembly programming, and manual D/A (digital to analog) conversion using R-2R ladders. Here’s what I built:
I’m skipping the schematic to save some time – basically it’s a ATmega88 with 6-pin programming header, power, a 16 MHz crystal (other frequencies also work, lfuse for this setup if 0xFF) and a red LED that is not used. The R-2R ladder is wired with white jumper wires to PB0-PB5 (it’s a 6-bit DAC) so that PB0 is the “least significant bit” and PB5 the most significant one. Read on for details.
Immediately after soldering together my USB password thingy, my solder iron, the family heirloom Weller Magnastat stopped working. Some investigation showed that the base station was providing 24V AC voltage just fine, so I decided to unassemble the handpiece to see if something could be done. Here’s what I found:
It turned out my iron was salvageable; read on to learn a bit about the Magnastat and how I was able to repair mine.
Having done half a dozen V-USB tutorials I decided it’s time to whip up something cool. As USB keyboards were an area untouched, I decided to make a small USB HID keyboard device that types a password stored in EEPROM every time it’s attached. A new password can be generated just by tabbing CAPS LOCK a few times (4 times to start password regeneration and one tab for each password character generated, 10 is the default password length). Below you can see the device in action:
The place I work at requires me to change my password every few months so this would be one way to skip remembering a new password altogether (as long as I remember to write it down before regenerating a new one so password can be changed :).
What is inside?
The device is powered with a simplified version of the hardware I used in my ATtiny85 USB tutorial – I stripped away the LCD, reset pullup and both capacitors. If you’re better in cramming components inside enclosures I suggest adding at least a 0.1 uF capacitor between VCC and GND, but it seems to work fine even without it:
