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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I2C Pull-ups with Multiple Power Supplies

If I have an I2C Master with multiple I2C Slaves all on separate 3V3 lines (i.e. 3v3_Master, 3V3_Slave1, 3V3_Slave2... etc.) does it matter which 3V3 line the pull-up resistors on the line connect to? ...
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385 views

High-Side Current Sensing; I2C

I am beginning a project that requires the sensing of a very small current (in the nA range) from a 3000V supply. The application is such that it can only be done on the high side. The data needs to ...
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2answers
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Weird reading from NAU7802 ADC

I'm using an NAU7802 ADC which has a built in amplifier. I'm trying to use it to read a strain gauge but it keeps giving me weird readings. Eventually I resorted to shorting the two differential ...
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1answer
566 views

I2C clock frequency variations

I am using an I2C peripheral in PIC18 series running at 100 kHz and I have used pull up resistors of 4.7 k\$\Omega\$ in the process. I then loaded a code with continuous write operation of EEPROM and ...
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1answer
180 views

Debug of data transmission via I2C

I was able to generate I2C transmission through micro controller but still i have a doubt on certain things. First being, if we send a data like 0x0a, then we can monitor the data as it is a single ...
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2answers
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Can ATmega88 be run at 3.3V with internal clock?

I want to use a few ATmega88s with Arduino bootloaders to act as I2C stepper drivers and temperature controllers that will interface with a Raspberry Pi. The thing is just that it seems the RPi ...
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1answer
886 views

I2C function for PIC

I wrapped a function for I2C initialization on PIC18F26J50 and it happens to be somewhat like this: ...
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3answers
796 views

Why only 127 slaves in I2C?

Since the slave addresses are 7 bits long, why is it that the number of slaves can be only 127? Is one of the addresses reserved for some special purpose?
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1answer
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i2c over gpio - level shifter

I'm quite new to this. I have just basic background in electronics. So I would appreciate an advice from someone more experienced. I would like to connect an i2c display to my tp-link wr703n (ar9331) ...
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5answers
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i2c automatic address assignment

I have asked the question here and someone offered to ask here in order to get better answers, so here it is: History: I decided to design a circuit with some peripheral ic's. Although SPI ...
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4answers
2k views

i2C : pull-up resistors “design pattern”, Shielded cable and connector?

I'm designing an arduino based board which will uses I2C port a lot. I want to be able to connect several slave devices, and/or connect several mother boards together (at least 4 would be great). The ...
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4answers
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Which interface is better for my OLED display?

I have a 0.96 inch 128x64 Yellow-Blue OLED display module like this: OLED module and I want to use it for a project. The Driver of it is SSD1306. if you see in the datasheet of SSD1306, you will know ...
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404 views

How to “read” SSD LED display by sniffing it's i2c communications with master?

Firstly I apologise if this question is more of a Raspberry Pi/Linux question but I've scoured the Raspi/Linux stack exchange boards and googled until my fingers fell off so I'm trying here in the ...
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2answers
115 views

Signal buffer/converter/recorder

Is there an IC that will "record" a digital signal received (highs and lows) record or buffer that input, and finally send to another IC thru I2C interface. The problem is that I have two different ...
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4answers
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Multiplexing I2C devices with MOSFETs

Ok, I understand similar questions have been asked in the past, please bear with me. Here is my problem, I have 2 I2C devices to be connected to a single I2C bus. They happen to be the same component ...
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3answers
726 views

selectable power voltage

I want to build a circuit that will output multiple voltages (one at a time) to supply an FPGA. The core volt will be constant voltage. I want to be able to supply different voltages for the FPGA ...
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2answers
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Protecting 3.3V I2C lines

Raspberry Pi has 3.3V I2C bus without any protection against overvoltage. So, I want to add protection against an accidental 5V level on the bus. How to do it? My two tries: simulate this circuit &...
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1answer
3k views

Can't get I2C to work on PIC32 (“skips” bytes/hangs)

I am working on a PIC32-MAXI-WEB development board from Olimex that I'd like to have communicating with an Invensense MPU-6050 6DOF accelerometer/gyro. By modifying an demo from Olimex I managed to ...
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1answer
386 views

I2C with only ground common

I'm playing with I2C on an AVR. I need the devices separated, and each device has its own battery. For the I2C I'm not clear if it is OK to have the pull up resistor within the source device, then ...
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3answers
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I²C, SPI, CAN protocols and the OSI model

Is there a reference or what is the explanation for I²C and SPI being just physical layer protocols in the OSI model (I know that this model is for communication and maybe not exactly for on-board ...
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1answer
713 views

How to improve I2C RTC accuracy

I´m using a PCF 8583 I2C RTC for one of my projects (i´m not a professional, just an amateur). The clock delays about an hour per day, which I find unacceptable. I´m using a 32768 Hz, 12.5 pf, 50 ...
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674 views

L3G4200D random spikes

I've searched this forum a bit in regards to the L3G4200D gyroscope, and haven't seen this problem mentioned, but I have seen others talk about it on other forums. I am seeing a strange large value in ...
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1answer
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IC: I2C communications over a DC bus

I have been looking everywhere for a method to use i2c over a 12-48V DC power bus. Are their any current IC solutions that I could check out? If not where would be a good place to start on such a ...
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1answer
849 views

i2c + 7 segement serial display + ATtiny85

I have a project that requires a 7 segment display and I was trying to get away with using the smallest micro controller possible. Does anyone see any problems with connecting an ATtiny85 to a 7 ...
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1answer
1k views

Interfacing with an LCD screen

I have managed to salvage the LCD screen from an old Tom-Tom (the model number of the screen is LTE430WQ-F0B-0BS). It comes with a driver for the screen on the back, but it doesn't look humanly ...
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2answers
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Problem with transmitting data from PIC18F45K20 (C18) to MCP23017

I am currently testing the MCP23017 (slave device) 16 bit I/O Expander using a PIC18F45K20 with the C18 compiler to transmit data to the MCP23017. The address pins (A0, A1 and A2) of the MCP23017 are ...
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1answer
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I2C Raspberry Pi to PIC24F

I'm new to PIC's and PIC programming but I'm working on a little project to try get a PIC24F32KA301 to communicate with a Raspberry Pi using I2C. The Raspberry Pi is the master and the PIC is the ...
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4answers
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Determining I2C Address without Datasheet

When setting up I2C communications, I know that it is certainly ideal to have the devices' datasheet(s), and find the I2C address of the device(s) that way. However, in some reverse-engineering ...
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2answers
5k views

How to connect ATTiny45 to Arduino via serial/spi/i2c and send data?

I am trying to create a smart alarm system for my house. I want to have one arduino as the master and several other AtTiny's as slaves to collect data as temperature, moisture, gas concentration, ...
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1answer
531 views

How do I connect non-I2C devices to an I2C bus?

I'm quite new to electronics and just trying to do my first Raspberry Pi based system: one diode, one pressure sensor and LCD 1602 with keypad shield (the one for an Arduino board). The way I'd like ...
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3answers
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Can this AVR MCU with 5V I2C work with this sensor with 3.3V I2C?

I'd like to interface an MPU-9150 sensor with an ATmega128 using I2C. The Atmega operates at 5V while the sensor chip operates at 3.3V. How can I find out if the two can work together? I'm not very ...
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How to add additional I2C sensor module on Arduino

I have tried the GY-521 sensor on Arduino by using the guide from (http://playground.arduino.cc/Main/MPU-6050). It worked well. Can anyone guide me on how can I add another GY-521 module please? I am ...
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0answers
487 views

Burst mode data errors on I2C

I'm using burst mode to read 14 bytes from a sensor via I2C running at 400KHz. The problem is that there are periodic errors on the last byte of the packet, that come in roughly every 8 reads. The ...
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1answer
842 views

Bad clock pulse on I2C EEPROM read

I am seeing a strange behaviour on an I2C waveform, and it is causing an incorrect bit to be read by the master. The master device is an ET1200 EtherCAT ASIC, and my slave is a CY8C3666LTI PSoC which ...
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1answer
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How much max distance of SPI & USB & I2C and TWI(without any IC [closed]

How much max distance of SPI & USB & I2C and TWI(without any IC(my mean is directly)), and how can i amplify these?
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1answer
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Adafruit SSD1306, I2C, ATmega1284p: OLED Display askew/misaligned

Another strange problem here. The setup: Adafruit SSD1306 OLED board connected to an ATMega1284p via I2C. Since I "upped" my 1284 to 8MHz (which I needed to to reliably talk to my temperature ...
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1answer
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1-Wire DS18B20 on mighty 1284p can't find my sensors, same sensors work w/ Duemilanove

I have uploaded the DS18x20 Temperature example sketch (unaltered, except I tried multiple pins for the I2C communication) to my proven Duemilanove and my ...
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1answer
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Msp430g2553 i2c communication library with itg3200 gyroscope

I've been creating an I2C library for communicating with ITG3200 gyroscope for MSP430g2553 experimental launchpad. I still have slight problems with sequential reading and the signed values but I'm ...
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4answers
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On multi master i2c bus how to determine which device is the master of the bus?

On a multimaster i2c bus, how to determine which device started the transfer? update (from comments made below by the O.P.) : I am trying to make sense of http://www.i2c-bus.org/serial-resistances-...
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1answer
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should I use 2 SPI devices on Arduino UNO/PRO or 2 I2C devices?

I am using a microSD breakout board and the accelerometer ADXL345 https://www.sparkfun.com/products/9836. each one alone works perfectly fine, but once I put both (sharing pins 11,12,13, but with ...
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336 views

Reading from an ITG-3200 Gyroscope

I'm having some trouble getting any reading from an I2C ITG-3200 Gyroscope breakout I'm using from Sparkfun. Here is the product: https://www.sparkfun.com/products/9801 I have a feeling this might be ...
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0answers
3k views

Msp430 I2C Single Byte Read Write

I have this code I've been working on that connects an ITG-3200 gyroscope slave and MSP430G2553 master via I2C bus. It was working fine yesterday but somehow today it is not working. I tried to debug ...
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1answer
213 views

What are some good older devices that I can scrounge i2c or spi modules from?

I am a newcomer to electronics design and I'd really like to start fiddling with making my own circuits. I have a raspberry pi which has both I2C and SPI interfaces, and I'm wondering if there's any ...
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2answers
543 views

Multiplex two I2C ICs into four 7 Segment displays

I currently have two PCF8574AN I2C 8-bit IO expander ICs. Is there a way I could have two seven segments be driven off one IC (So i could run four seven segments displays off the two ICs that I have). ...
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6k views

How to deal with multiple pull-up resistors on modules

I was thinking about doing a modules for a development board I did a few days ago that will include spi/i2c interfaces. The problem is that I didn't included pull-up resistors in the MCU pins in the ...
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1answer
48k views

Msp430 I²C single write-read example

I've been trying to use an I²C bus between a MSP430G2553 launchpad and ITG-3200 gyroscope breakout. Here is the Launchpad datasheet and user guide and the ITG-3200 datasheet. The ITG-3200 uses a ...
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1answer
446 views

I2C protocol for PIC18F45K20 with C18 compiler

I'm currently trying to receive data from the 2-wire serial interface of an image sensor with a PIC18F45K20 written with C18 in MPLAB X IDE v. 1.41. How do I initialize the I2C protocol and how do I ...
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2answers
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Does polling a DS1307 too frequently affect accuracy?

I did some research, and I found contradictory response on the web. I'm polling a DS1307 on an loop, with an Arduino, that takes about 20 ms to run, so basically I'm polling the I2C interface 50 times ...