Mitigate interference

Interference presence can be detected using the NetworkAnalysis example and its results. If the bus is detected many times busy, this may mean that interference in induced on the bus. AC wiring can induce the 50Hz wave in a PJDL bus if close enough (see video demonstration).

Pull-down resistor

A pull-down resistor is commonly used to discharge induced interference.

I/O PIN ------------------- BUS
                      |
GND -------[/\/]------/

           resistor 500 KΩ - 10 MΩ

The correct resistor value to be applied is very variable (500 KΩ - 10 MΩ) depending on the bus topology and interference magnitude, but it is often near to the mega ohm order. To find the correct resistor value run the NetworkAnalysis example and start testing the resistors in descending order until the number of busy is around 0.

Ferrite bead

If interference and or CRC errors are still present, a strong palliative is the use of ferrite beads. Many devices where digital communication is used are equipped with it (see Sony Playstation wired controller).

              _______
             |       |
I/O PIN -----|-------|----- BUS
             |_______|

            ferrite bead

Power supply filtering

Bandwidth loss related to the system's power consumption is the sign of power supply interference. Try to avoid when possible to feed devices with a power supply shared with highly demanding appliances like servos, motors or actuators. If it is required, at least place a diode connected to VIN, able to block inverse current from the VIN pin back to the wire and use a capacitor to fill temporary feeding shortages.

GND ------
         |    
        === capacitor
         |
VIN ---------[|__]------- POWER SUPPLY FEED

             diode

The solution described above can reduce but not eliminate transient voltage spikes.

Diodes in opposition

A more decisive way to deal with transient voltage is to use diodes in opposition. This technique reduces the short duration electrical spikes that can occur because of power shortages or power transitions in other large equipment on the same power line.

             diode                       diode

GND ---------[__|]--------------|--------[__|]--- POWER SUPPLY FEED
                                |                
                /-----[/\/]-----/  
                |
                |     resistor
I/O PIN  -------|-------------------------------- BUS