Treadmill safety module

A safety module for a motor speed control circuit, when speed control circuit has a failure mode in which full power is applied to the motor being driven by the speed control circuit, which is coupled to power terminals of a motor, the safety module comprising:

• a high pass filter followed by a low-pass filter coupled to the variable voltage power output of said speed control circuit;
• a threshold member coupled to an output of said high pass filter for passing a signal only if a change in the signal exceeds a predetermined value;
• and
• a semiconductor short-circuiting switching device coupled to said threshold device and coupled to said power terminals of the motor and to said output of said speed control circuit for shorting out said output of said speed control circuit responsive to an abrupt increase in a signal at the output of said speed control circuit which exceeds said predetermined value at the output of said speed control circuit.