Circuit and method for checking the contacting of a switch or pushbutton

Method for testing the correct contacting of a switch in a d.c. circuit, said switch being connectable alternatively with at least one output and at least one input of a computer, said method comprising:

• providing a checking circuit having a capacitor arrangement connected with the switch;
• connecting the switch at least initially with an output said computer;
• generating a signal level at the output of the computer, said signal level corresponding to a signal level which will exist in the case of correct contacting and actuation of the switch;
• changing the signal level;
• following changing of the signal level, connecting the switch at least with the input of the computer;
• and
• said computer evaluating the signal level.

Method for testing correct contacting of a switch in a d.c. circuit, said switch being connectable alternatively with at least one output and at least one input of a computer, said method comprising:

• providing a checking circuit having a capacitor arrangement connected with the switch;
• during operation of said switch at a known first signal level attributable to actuation of the switch, generating a second signal level through the output of the computer and applying said second signal level to said switch;
• deactivating the output;
• and
• checking proper contact of the switch, based on time variation of the signal level.

A circuit for checking proper operation of a switch in a d.c. circuit, comprising:

• a reactive circuit element connected with said switch;
• a voltage source for applying a biasing voltage to a first terminal of said switch at a first voltage level;
• a microprocessor for temporarily switching the biasing voltage temporarily to a second voltage level during a testing phase;
• a discharge path for discharging said reactive circuit element following a temporary switching of the biasing voltage;
• wherein said computer measures voltage at said first terminal during time periods immediately before and after a switching of said biasing voltage and compares measured voltages with a predetermined voltage level.