PWM + I2C interference in fan controller

Hans H. Guest #6005269
Rate this post
• ▲ useful
▼ not useful 
Hi,

I'm building a fan controller for a vintage computer and I'm facing some 
difficulties isolating the I2C bus and the motor PWM.  When I have a fan 
connected to the output, spikes are being introduced into the I2C bus 
which sometimes causes misreadings of the LM75A sensor data.  Can anyone 
suggest a simple way how I can decouple the two parts of the circuit 
better?

Please see the attached schematics and an image from my oscilloscope 
that shows the spikes.

Thanks!
Hans
Attached files:
Reply Quote Edit Move Thread sperren Anmeldepflicht aktivieren Anpinnen Delete topic Thread mit anderem zusammenführen Report post
K. S. #6005660
Rate this post
• ▲ useful
▼ not useful 
Hans H. wrote:
> Can anyone
> suggest a simple way how I can decouple the two parts of the circuit
> better?

show us your layout. I guess there is a significant problem with it like 
bad ground routing, no decoupling, signal paths next to power paths ...

2N7000 @ 3V3 GS can only drive <<100mA, it is only specified for 4.5V 
and its maximum threshold voltage is 3.0V. You need a real logic level 
Mosfet unless you use a toy ventilator with very minor current 
consumption (like a few mA max).
Reply Quote Edit Delete Report post
Watch this topic

Reply

Please log in before posting.

Existing account

or

Log in with Google account

No account?

Registration is free and takes only a minute.

Register now