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
- reduce the pullups to 1k instead of 4k7 - disconnect the 100nF at the diode - connect 100nF between 3.3V anf GND
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).