Category Archives: i2c

Taking the Leap Off Board: An Introduction to I2C Over Long Wires

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If you’re reading these pages, odds are good that you’ve worked with I²C devices before. You might even be the proud owner of a couple dozen sensors pre-loaded on breakout boards, ready for breadboarding with their pins exposed. With vendors like Sparkfun and Adafruit popping I²C devices onto cute breakout boards, it’s tempting to finish off a project with the same hookup wires we started it with. It’s also easy to start thinking we could even make those wires longer — long enough to wire down my forearm, my robot chassis, or some other container for remote sensing. (Guilty!) In …read more

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Bus Pirate Commandeers I2C

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The Bus Pirate is one of our favorite tool for quick-and-dirty debugging in the microcontroller world. Essentially it makes it easy to communicate with a wide variety of different chips via a serial terminal regardless of the type of bus that the microcontroller uses. Although it was intended as a time-saving prototyping device, there are a lot of real-world applications where a Bus Pirate can be employed full-time, as [Scott] shows us with his Bus Pirate data logger.

[Scott] needed to constantly measure temperature, and the parts he had on hand included an LM75A breakout board that has a temperature …read more

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PURE Modules Aim to Make Prototyping Easier

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[Sashi]’s PURE modules system wants your next wireless microcontroller and sensor module project to be put together using card-edge connectors. But it’s a lot deeper than that — PURE is an entire wireless gadget development ecosystem. Striking a balance between completeness and modularity is very difficult; a wire can carry any imaginable electronic signal, but just handing someone a pile of wires presents them a steep learning curve. PURE is at the other end of the spectrum: everything is specified.

So far, two microcontroller options are available in the system, the nRF52 series and TI’s CC2650. Both of these run …read more

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DIY I2C Devices with ATtiny85

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[Pawel] has a weather station, and its nerve-center is a Raspberry Pi. He wanted to include a light sensor but the problem is, the Pi doesn’t have a built-in ADC to read the voltage off the light-dependent resistor that he (presumably) had in his junk box. You can, of course, buy I2C ADC chips and modules, but when you’ve already got a microcontroller that has ADC peripherals on board, why bother?

[Pawel] wired up a tremendously simple circuit, downloaded some I2C slave-mode code, and added an LED for good measure. It’s all up on GitHub if you’re interested.

We’re covering …read more

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How I²C EEPROM Talks to the Bus

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You will probably be familiar with I²C, a serial bus typically used for not-very-fast communication with microcontroller peripherals. It’s likely though that unless you are an I²C wizard you won’t be intimately familiar with the intricacies of its operation, and each new device will bring a lengthy spell of studying data sheets and head-scratching.

If the previous paragraph describes you, read on. [Clint Stevenson] wrote a library for interfacing I²C EEPROMs to Arduino platforms, and when a user found a bug when using it on an ATtiny85, he wrote up his solution. The resulting piece is a clear explanation …read more

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When You Need a Scope, You Need a Scope

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Sometimes there’s just no substitute for the right diagnostic tool. [Ankit] was trying to port some I2C code from an Arduino platform to an ARM chip. When the latter code wasn’t working, he got clever and wrote a small sketch for the Arduino which would echo each byte that came across I2C out to the serial line. The bytes all looked right, yet the OLED still wasn’t working.

Time to bring out the right tool for the job: a logic analyzer or oscilloscope. Once he did that, the problem was obvious (see banner image — Arduino on top, ARM on …read more

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Three Arduinos, Sixteen Square Waves

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[Folkert van Heusden] sent us in his diabolical MIDI device. Ardio is a MIDI synthesizer of sorts, playing up to sixteen channels of square waves, each on its separate Arduino output pin, and mixed down to stereo with a bunch of resistors. It only plays square waves, and they don’t seem to be entirely in tune, but it makes a heck of a racket and makes use of an interesting architecture.

Ardio is made up of three separate el cheapo Arduino Minis, because…why not?! One Arduino handles the incoming MIDI data and sends note requests out to the other modules …read more

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What Could Go Wrong? I2C Edition

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I should really like I2C more than I do. In principle, it’s a brilliant protocol, and in comparison to asynchronous serial and SPI, it’s very well defined and clearly standardized. On paper, up to 127 devices can be connected together using just two wires (and ground). There’s an allowance for multiple clock-masters on the same bus, and a way for slaves to signal that the master to wait. It sounds perfect.

In reality, the tradeoff for using only two wires is a significantly complicated signalling and addressing system that brings both pitfalls and opportunities for debugging. Although I2C does reduce …read more

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I2C Bit Injection Adds Memory Banks To Everything

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[Igor] wished to upgrade his newly acquired radio — a Baofeng UV-82 — with a larger memory for storing additional scanning channels, and came up with a very elegant solution: Replacing it’s EEPROM with a larger one and injecting the additional memory address bits into the I2C data line.

The cheap handheld radio comes with an 8192 bytes large 24c64 EEPROM, which allows it to store 128 channels along with a few other persistent settings. The radio’s firmware sends two-byte memory addresses over the I2C bus when accessing the 24c64, but since the 24c64’s largest address is B00011111 11111111, these addresses always roll in with …read more

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