Dear friends,
I am working on an I2C project and I need to know if by adding 2x leds on SDA & SCL, could harm my network transmission?
I want to do it by using a 1K resistor in series with the led and connected to 5V.
Is it possible?
I am using this chip
Adding a led with resistor directly in the SDA and SCL line will certainly harm the communication.
The chip PCF8574 is an I2C I/O expander. That will not harm the communication, it is a i2c device.
That chip can drive up to 50mA. So that's no problem at all.
Do you expect to see the communication on the I2C on the LEDs? I2C communication has a frequency of at least 100kHz. So the LEDs might get a little less bright while communication is active but you won't notice a relevant flicker or anything like that. It's much too fast for our eyes to recognize.
So as you say it doesn;t harm my communication at all.
How is this protocol used? GND on standby and 5V when transmitting/receiving?
or the opposite like Arduino serial?
The I2C bus works by pulling down or letting the line float and being pulled up by an external resistor.
So how am I supposed to connect the led to SDA or SCL?
I am thinking of connecting the anode of the led to SDA/SCL in series with a 1K resistor connected to gnd. Is it correct?
I want the led to light up only in transmit/receive and NOT light up when its not sending/receiving data.
No.
Anode to +5V, cathode to the resisto and resistor to the signal line. Note that this might disrupt communications as you are asking the device to sink another 5mA of current.
nathanas:
I am working on an I2C project and I need to know if by adding 2x leds on SDA & SCL, could harm my network transmission?
I am using this chip
http://www.ti.com/lit/ds/symlink/pcf8574a.pdf
If there might be a problem with my communication I won;t use the leds.
Take a look at the datasheet it is supposed to support leds. and please feel kind to share your final opinion about this issue, with us.
Should I connect the resistor to SDA or SCL cable?
The datasheet says that the output ports of the device can support/drive LEDs. If you put LEDs on your I2C bus without some kind of high impedance buffering (like an op-amp) so as to not load the bus down, you will have comm problems.
Thanks a lot I won't use leds to my projects afterall...
Thanks a lot for your help!