Can I2C and PWM be in the same connector?

Thread Starter

Younes Thabet

Joined Jan 9, 2019
56
Hello all,

I have a daughter board that resides about 1m far from main board, this daughter board contains buzzer and some ICs. I am already worried that I2C won't work properly over this long distance and now that I added PWM, I am afraid that will disturb I2C and lose connection between the 2 boards.
any suggestions on how to handle this!? meaning can I use both I2C and PWM in one 6pin connector (SCL|GND|SDA|5V|PWM|12V)?

Thanks,
 

Papabravo

Joined Feb 24, 2006
16,773
Hello all,

I have a daughter board that resides about 1m far from main board, this daughter board contains buzzer and some ICs. I am already worried that I2C won't work properly over this long distance and now that I added PWM, I am afraid that will disturb I2C and lose connection between the 2 boards.
any suggestions on how to handle this!? meaning can I use both I2C and PWM in one 6pin connector (SCL|GND|SDA|5V|PWM|12V)?

Thanks,
It is worthwhile to consider that I2C does not run at a fixed speed. You have some flexibility in adjusting the speed to suit the environment. The wire guage of the conductors, the insulation material, and the conductor separation will all have an effect on signal propagation. Longer cables means that the I2C "driver" must cope with a large capacitive load. As such you can adjust the bit rate to a slower value to compensate for the slower rise and fall times. It also helps to know where in the bit cell the receiver will determine if a bit is high or low.

The other thing to be mindful of is GROUND differential between the ends of the cable. I2C is single ended, not differential.

If it was me I would put together a "reliable communication" test in the absence of any disturbance. for example lets say were are interested in the error rate of passing say 10,000 bits between the two. Now start adding disturbances and see what happens. If the disturbances affect the bit error rate then you can try different things, but after any change you have a baseline of information tell you if things have improved or not.
 

GetDeviceInfo

Joined Jun 7, 2009
1,875
What current is on the PWM. Shouldn’t be a problem if it’s a signal, but if it’s a driver, you could consider putting the pwm generator on the end of the I2c.
 

GetDeviceInfo

Joined Jun 7, 2009
1,875
If it’s already done, then testing, as mentioned, is a realistic option. I would put a dummy load on the pwm and crank it up to see where interference crept in, then make a determination as to the current levels that are acceptable.
 

Janis59

Joined Aug 21, 2017
1,346
Generally i2c is dedicated to SHORT and INTRA-PCB traffic. That is VERY serious. However, there are trick named P82B715 Extender (about 4 USD per piece) what gives hardly robust noise-immunity thus the line may go up to 3 meters and with significant loss of speed even 40 meter. Without of it, with significant loss of speed is 20 cm, and with full speed about 5 cm (ONLY!!).
 
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