The develop of this kind of electro-static charge in plants, where belts are running on rollers, both made of rubber or plastics can be very very dangerous, can even kill people and cause fire! This principle of separating charge and generating high voltage by belts and rollers made of rubber is even used in fundamental physics to produce millions of volts, by a machine that is called Van de Graaff generator, to accelerate charged fundamental particles!

Coating of antistatic material on the belts or rollers will not help at all, because the charge is still generated (concretely spoken separated). Only by doping the material of which the belts and rollers are made by conducting material like carbon or graphit will cure the problem. Then, the charge separating mechanism is "short-circuited" and charge can no longer be seperated. But such belts and rollers are expensive!


Forget the watchdog!
Such a microcontroller is a higly dynamically working thing. Even when looking like a statically working chip, several microroutines are running internally all the time, which can easily be interfered by injecting noise into the port lines or supply pins, right what an ESD-event does. So, when the micro hangs-up, due to an ESD-event, this does not mean, that you can make it commence properly by simply resetting it. Remember, a hanging micro is a chip totally running ill, becoming hot and being in danger to be destroyed! The only way to terminate the hang-up is to power-down the micro and power-up it again! And this cannot be done by a watchdog. More, if really ESD contaminates your application, you will even run into danger to end with a hung-up watchdog too...

ESD is normally fought against by a three level strategy:

1. Preventing electro-static charge from being generated.

For instance, by exclusively using antistatic material, means doped rubber or plastic (see above).

2. Shunting the (unavoidable) ESD-events arround the mirco, by offering it a low impedant path to protection earth, where all the ESD-events finally want to travel to.

Protect each line running to the micro by connecting a ceradiode, transzorb or varistor to signal ground, while the signal ground is connected to enlosure by a capacitor. When the enclosure is now connected to protection earth (green-yelllow PE-cable), by this way the ESD-events are shunted to protection earth, before entering the micro's board. So, do this right at the switches or lines, just where the according signals enter the enclosure. And remember, ESD has strong harmonics in the GHz-range, so every millimeter counts!!! This means, that normallay SMD parts must be used for all this filtering and protecting stuff and that ultra short connections have to be provided!!

3. Filtering of the remaining energy of ESD-events, that couldn't be totally shunted to enclosure.

Simple RC-low pass filters or ferrite beads can limit the remaining ESD-energy hitting the micro to a sane level, no longer allowing the micro to hang-up.

Kai