Questions tagged [i2c]

I²C (Inter-Integrated Circuit) is a multi-drop serial bus invented by Philips (now NXP) for communication between ICs on the same PCB, i.e. short distance.

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BMP085 and Humidity and Temperature Sensor with arduino

I am doing a project that requires me to use a BMP085 (with breakout) and a humidity/temperature sensor (with Breakout). I am trying to attach both of these to the arduino uno through two analog ...
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What is the speed of I2C for AVR communication?

I'm doing a project where I'll have a lot of slave ATtiny's and one master controller (either an Arduino/ATMega or an mbed). I assume the ATtiny with it's low clock speed of 10MHz will be my ...
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618 views

OpenServo and I2C Syncronization

I need to send a command to multiple I2C devices on the same wire. The devices are OpenServos. Each device get's it command and begins processing the information in the command. How do I ensure that ...
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1answer
355 views

Programmable DS1077 Oscillator: Cannot set the DIV register

I am trying to run a Maxim DS1077 programmable oscillator through the I2C bus from an Arduino Uno development platform. I am able to run the oscillator at the different pre-scaler values 1,2,4, and 8. ...
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I2C 5 <-> 3.3V Interface Chip

Does the classical 5V <--> 3.3V bidirectional MOSFET interfacing solution exist as a DIP package? Or is the commopn way to place discrete MOSFETs in your circuit? In that case, what are some common ...
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843 views

How can I get touchscreen (HID) data into Windows 7?

We have a hardware design in progress that is taking touch screen inputs and passing them along via I2C to an FPGA. The FPGA translates the I2C data to PCIe. The PCIe passes the touchscreen data to ...
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I2C routing configuration

I have several slave devices communicating with a microcontroller master on an I2C bus. My PCB is only about 1" x 1" and the devices are only communicating at 400 kHz. What is the best way to ...
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2answers
599 views

Reading back 0xffff for temperature from I2C BMP085 temp/pressure sensor

I'm interfacing a Rabbit 5760 CPU to a Bosch BMP085 sensor via I2C. Everything is fine except reading the temperature register is reading back 0xffff (see BP_FINISHTEMP case in switch). I can't see ...
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Reading empty (new) AT24C16 I2C EEPROM - 0xFF or 0x00?

What byte vaule should I see when reading empty EEPROM chip via I2C?
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1answer
192 views

disabling internal pullups on D0 && D1 on AT90USB1286

Can anyone just verify quickly for me that this: cbi(PORTD, 0); cbi(PORTD, 1); will disable the internal pullups on the AT90USB1286? I'm trying to avoid damaging ...
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I2C - Cannot read temperature from TC74 with PIC16F887

The question was: I want to read temperature from TC74 using I2C module of PIC16F887, however, in Proteus simulation, I see noises in I2C Debugger Tool's output. ...
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Circuit only works when o'scope probe is connected

I am working on a circuit with a PIC mcu and an LCD display on a breadboard. The PIC communicates with the display via I2C. For some reason I can only get the communication to work properly when my o'...
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833 views

How can I cope with small internal pull-up resistors on an I2C bus?

I have an I2C sensor that has a some 89kΩ pull-up resistors on the SDA and SCL lines. The controller I'm using has 2.2kΩ internal resistors on these lines as well. I'm worried that the sensor won't be ...
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General protocol for data transfer from one system to another?

What is the general protocol to send information from one system to another? For example, let's say we have some information collected from microcontroller over a length of time that we want to send ...
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1answer
990 views

Advice a humidity sensor with I²C interface

I like to interface a humidity sensor over the I²C bus. It should come in a small package, and consume little power. Accuracy isn't that important. I'm using the DS1621 as temperature sensor, I'd ...
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1answer
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Picotux alternatives available? [closed]

I wanted to use a tiny Linux computer to read data from I²C bus. I knew there was Picotux, and I was thingking about buying one. But the website is down, so I guess there's no Picotux anymore. :( ...
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Is there an I²C device out there for reading a set of PWM inputs?

I'm thinking about getting a bunch of Maxbotix Ultrasonic rangefinders. I'd like to use as few pins on my controller as possible. Since I don't think you can have multiple devices on an RS232 serial ...
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1answer
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How do I read I2C memory with an Arduino?

I have HH100D humidity sensor. It outputs a frequency signal, which I know how to handle. However, it also has a small EEPROM with calibration values that is available via I2C. Those values are ...
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620 views

Don't understand how these resistors operate in this circuit

When reading a manual on using a PICAXE and an I2C device I saw this diagram. I can't work how this would behave as wouldn't it make the connection on the lines constantly high due to the connection ...
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How do I get an Arduino (5 V) and MPR121 (3.3 V) to talk?

I have the Sparkfun MPR121 I2C Capacitive touch sensor breakout board I have read that it uses 3.3 V, I know that I can't just connect up the 3.3 V power supply output from the Arduino as the ...
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1answer
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Using MLX90614 OR is I2C and SMBus compatible?

I am trying to use a Melexis MLX90614 with Atmega8. I have failed in all my attempts till now. I tried sending this sequence ...
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I2C brushless DC motor controller?

I'm designing a robot and I'm looking to use mainly I2C to control different sensors and stuff. I'm now looking into motors, specifically this motor. However all of the ESCs I have seen use a PWM ...
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Invensense IMU3000 with PIC

Has anybody experienced using the Invensense IMU3000 gyroscope with some microcontroller? The hardware comes with a really good library integrating full control of its features. This library is ...
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2answers
648 views

What kind of issues might I face when moving from 400 kHz I2C to 1 MHz I2C?

I'm thinking of migrating from an I2C bus at 400 kHz to one running at nearly 1 MHz. I am using 1.2k pull-ups at the moment and on the clock and data lines, I get a rise time of 383ns average when ...
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3answers
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I²C level shifter pulls low side up

I am using the well-known I²C level shifter from that appnote from Philips. The 3V side is supplied by an LP2950-3.0 regulator and is loaded only moderate (a few quite lazy 74's). The problem I'm ...
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Confused about I2C addressing in PCA8574/74A

The datasheet for the NXP PCA8574/74A contains the following line on addressing (p.6): When AD2, AD1 and AD0 are held to VDD or VSS, the same address as the PCF8574 or PCF8574A is applied. I'm ...
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What I2C address should I choose?

Now I know in order to have an I2C address reserved for yourself you have to pay the I2C people some money. But I don't want to do this. I'm asking for advice on what address I should choose for my ...
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Using I2C Devices on SMBus interface

I'm developing on a PC/104 stack which aparently has an I2C interface. However, on further investigation it is actually an SMBus interface but says the two are interchangable up to 400kHz. However, ...
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Is it possible to use 400 kHz I2C buses with a 32 kHz slave?

I am going to use a 400 kHz I2C bus, but I want to talk to a slave MCU, a PIC16F690 (datasheet), running at 32 kHz. Is it possible to do this? I think so, because the master does the clocking, but are ...
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Any tips on using the Invensense ITG-3200 gyro?

I'm developing a gyro+accelerometer data logging device using the Invensense ITG3200 gyro device and I'm having a real struggle getting it to talk to me. I have tried 5 of them and none of them are ...
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Comparator over I2C with programmable reference

I'm looking for a programmable comparator which has a digital or open-drain output and a voltage reference which can be programmed over I2C. My searches at my favourite sites of Microchip and Farnell ...
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253 views

Is it worth worrying about propagation delay differences when dealing with relatively slow protocols like I2C @ 400kHz?

At the moment I'm working on a system which will use a 400KHz I2C bus. The bus wires (SCL, SDA) are different lengths by a few cm, so the delay between them will be in picosecond to nanosecond range - ...
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8answers
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How to resolve I2C address clashes?

I want to connect multiple I2C slave devices to a micro controller all on the same set of pins but the I2C devices all share the same address. The addresses are fixed in the hardware. Is there any ...
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868 views

What is the most popular embedded serial bus? [closed]

I'm designing an embedded device that I would like to make interoperable with third party peripherals through a serial bus. Should I choose SPI, I²C, or some other bus? The peripherals will be ...
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Methods to test/debug I2C protocols? [closed]

I've been working on some digital designs with I2C command & control and need a PC-based tool to test my interfaces. -- In the past, I've used iPorts (MCC) to do these tasks but the price tag of ...
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Recommend any ADC ICs? [closed]

I am looking for an ADC IC and while I could just take the plunge and pick one, I was wondering if anyone had any experience with any particular devices? I need it to: Connect to an AVR via I2C/SPI (...
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I2C 7seg driver

Does anyone know of any good I2C 7segment display drivers. I swear a previous answer referenced a chip for this on chiphacker but I cannot find it. I would also be happy with SPI, but I I2C would ...
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Can't get DS1077 programmable oscillator to work

I'm trying to get the DS1077 to work, but I can't for the life of me figure out what I'm doing wrong. I'm using the defaults for the MUX and BUS registers, and programming in my own DIV frequency has ...
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8answers
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Is there a correct resistance value for I2C pull-up resistors?

The datasheet of the 24LC256 EEPROM states that: The SDA bus requires a pull-up resistor to VCC (typical 10 kΩ for 100 kHz, 2 kΩ for 400 kHz and 1 MHz). I thought that any resistor with a kΩ value ...
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419 views

Source for parts to make a BlinkM I2C bus cable? (from todbot blog)

I came across this post on the todbot blog about controlling BlinkMs over an I2C bus: http://todbot.com/blog/2008/06/17/get-on-the-blinkm-bus-with-a-blinkm-cylon/ I LOVE his connectors, but cannot ...
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SPI or I2C: which to use for a longish bus

I'm contemplating a project that would require several AVRs talking to each other over a bus. They'd be separated by as much as 6 feet. It seems like both I2C and SPI can let a series of micros ...
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4answers
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I2C 3.3 to 5.0 V conversion

I'm trying to interface a 3.3V I2C device to a 5V Arduino. I don't have any problem with SCL line. I can use a simple voltage divider but I have an issue with the SDA line as this is bi-directional. ...
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How to reverse engineer I2C and SPI protocols?

If I have an unkown device which talk I2C or SPI how can I reverse engineer the protocol. Basically I am looking for something similar as snoop or tcpdump. For software Mac is preferred but can also ...
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Implementing I2C to analog

How can I implement (or maybe there is an IC that already does that) a board whose input would be I2C and output would be analog voltage (0V - 5V) ? Eventually I would like to connect a couple of ...