AVR Barn Door Tracker for Astrophotography

zzjBarnDoorTracker

[ZigZagJoe's] first foray into astrophotography is this impressive AVR barn door tracker, which steps up his night sky photo game without emptying his bank account. If you’ve never heard of astrophotography, you should skim over its Wikipedia page and/or the subreddit. The idea is to capture images otherwise undetectable by the human eye through longer exposures. Unfortunately, the big ball of rock we all inhabit has a tendency to rotate, which means you need to move the camera to keep the night sky framed up.

Most trackers require precision parts and fabrication, which was out of [ZigZagJoe's] grasp. Instead, he found a solution with the Cloudbait Observatory model, which as best as we can tell looks vaguely similar to the tracker we featured last year. Unlike last year’s build—which uses an ATmega32u4 breakout board— [ZigZagJoe's] tracker uses an ATTiny85 for the brains, running a pre-configured table that determines step rate against time.

[Read more...]

Chachka: A Trinket Clone

Why would you clone something as cheap as the adafruit Trinket? Well, because you can, of course. And that’s exactly why [Ray] started to build a clone two days after his Trinket came in the mail. He encourages you to support adafruit by buying at least one Trinket before attempting a clone, and we agree. Besides, you’ll be able to use the support forum with a clear conscience.

[Ray]‘s design uses an 1800Ω pull-up resistor rather than the 1500Ω in the Trinket. He made this change based on his experience with V-USB and the ATtiny85. He has a lot more information on his build on the Arduino forum. Check out a short video of Chachka responding to a Sony-esque remote control after the break.

Need an application for your Trinket clone? Check out this incredibly well-built USB volume knob.

[Read more...]

The Tiniest SD Card Locker

sdlocker-tiny

In case you weren’t aware, that little ‘write protect’ switch on your SD cards probably doesn’t do anything. It’s only a switch, really, and if an SD card reader doesn’t bother to send that signal to your computer, it’s completely ineffective. Then there’s the question of your OS actually doing something with that write protect signal.

The better way to go about write protecting an SD card is using the TMP_WRITE_PROTECT bit on the SD card’s controller. [Nephiel] came up with an amazingly small device to set that bit, with the entire circuit fitting inside an old Playstation memory card.

[Nephiel] based his project on [Karl Lunt]‘s SD Card Locker we saw late last year. [Karl]‘s SD Locker uses an ATMega328 microcontroller, a pair of AA batteries, and an SD card socket to perform the bit toggling. This is still a very small device that fits inside an Altoids tin, but [Nephiel] thought he could make it smaller.

The new and improved version uses an ATTiny85 for SPI access to the SD card. A single button and LED serves as the user interface: with the LED off, the SD card is writable. Press the button, the card is locked, and the LED lights up.

Software Half Duplex UART for AVRs

One Wire Serial

If you have worked with very low cost microcontroller in the past, such as the ATtiny series from AVR, you’ve probably been stuck without a UART peripheral. The usual answer to this problem is to implement the UART in software. It’s not fast, but it works.

Lets say you’re even more limited on resources, and only have a single pin for UART. [Ralph] created a software library and a small circuit that enables half duplex UART using only one pin. With the above circuit, and a 62 byte Arduino compatible library, you can add UART to the tiniest of ATtinys.

In this circuit, the Tx/Rx pin is on the AVR, and the Tx and Rx pins are another device. The circuit relies on the idle state of UART being a logic high signal. When the Tx pin is idle, the transistor stays on. This allows the Tx/Rx pin to pull Rx low when the AVR sends a 0. When the Tx pin sends a 0, the Tx/Rx pin gets pulled low through the diode.

It’s a clever hack, and could definitely help add communication to your next tiny project.

A Vibrating Timepiece

vibratingWatch

It may not look like much, but the above pictured device is [qquuiinn's] handy little watch that indicates time through pulsed vibrations. Perhaps we should refrain from labeling it as a “watch,” however, considering it’s [qquuiinn's] intention to remove the need to actually look at the thing. Vibrations occur in grandfather clock format, with one long vibration for each hour, accompanied by one, two, or three short pulses for the quarter-hour increments.

The design is straightforward, using an ATTiny85 for the brains along with a few analog components. The vibration motor sticks to the protoboard with some glue, joining the microcontroller, a coin cell battery, and a pushbutton on a small protoboard. The button allows for manual time requests; one press responds with the current time (approximated, probably) in vibrations. The build is a work in progress, and [qquuiinn] acknowledges the lack of an RTC (real-time clock) causes some drift in the timepiece’s accuracy. We suspect, however, that you’d address that problem—twice daily—when you replace the battery: it only lasts ten hours.

Trimming The Fat From AVR GCC

avr

[Ralph] has been working on an extraordinarily tiny bootloader for the ATtiny85, and although coding in assembly does have some merits in this regard, writing in C and using AVR Libc is so much more convenient. Through his trials of slimming down pieces of code to the bare minimum, he’s found a few ways to easily trim a few bytes off code compiled with AVR-GCC.

To test his ideas out, [Ralph] first coded up a short program that reads the ATtiny85’s internal temperature sensor. Dissassembling the code, he found the a jump to a function called __ctors_end: before the jump to main. According to the ATtiny85 datasheet, this call sets the IO registers to their initial values. These initial values are 0, so that’s 16 bytes that can be saved. This function also sets the stack pointer to its initial value, so another 16 bytes can be optimized out.

If you’re not using interrupts on an ATtiny, you can get rid of 30 bytes of code by getting rid of the interrupt vector table. In the end, [Ralph] was able to take a 274 byte program and trim it down to 190 bytes. Compared to the 8k of Flash on the ‘tiny85, it’s a small amount saved, but if you’re banging your head against the limitations of this micro’s storage, this might be a good place to start.

Now if you want to hear some stories about optimizing code you’ve got to check out the Once Upon Atari documentary. They spent months hand optimizing code to make it fit on the cartridges.

Cloning the Trinket for a USB Volume Knob

LEDs

A while back, [Rupert] wrote a blog post on using V-USB with the very small, 8-pin ATtiny85. Since then, the space of dev boards for 8-pin micros with USB has exploded, the most recent being Adafruit’s Trinket. [Rupert] liked what he saw with the Trinket bootloader and decided to clone the circuit into a useful package. Thus was born an awesome looking USB volume knob complete with a heavy aluminum knob, rotary encoder, and RGB LED strip.

[Rupert] got his V-USB/ATtiny85/rotary encoder circuit working, and at the expense of a ‘mute’ control, also added an awesome looking RGB LED ring powered by Adafruit’s Neopixels. The PCB [Rupert] fabbed is pretty well suited for being manufactured one-sided. If you’ve ever wanted an awesome volume knob for your computer, all the files are available form [Rupert]‘s blog.

Just as an aside, [Rupert] has been working on getting the Trinket bootloader working on the ATtiny84, a very similar microcontroller to the ’85, but with eight analog pins. It’s a neat device that I’ve made a small V-USB breakout board for, but like [Rupert], I’m stuck on porting the bootloader. If anyone has the Trinket/Gemma firmware running on an ATtiny84, send that in. We’ll put it up.

Follow

Get every new post delivered to your Inbox.

Join 94,010 other followers