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A CIRCUIT FOR ELIMINATING ERRATiC SWITCH CONTACT OUTPUT

IP.com Disclosure Number: IPCOM000006260D
Original Publication Date: 1991-Dec-01
Included in the Prior Art Database: 2001-Dec-19
Document File: 1 page(s) / 50K

Publishing Venue

Motorola

Related People

Robert Ford: AUTHOR

Abstract

R6 output This circuit debounces a mercury switch in motion. Its output indicates the present status of the switch (dominantly open or closed). Debouncing is accomplished using a capacitor (Cl) voltage applied to the input of a transistor switch, Q3. When the capacitor voltage exceeds a threshold value, the transistor switch conducts. Both charging and discharging functions of the capacitor are employed.

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MOTOROLA INC. Technical Developments Volume 14 December 1991

A CIRCUIT FOR ELIMINATING ERRATiC SWITCH CONTACT OUTPUT

by Robert Ford

R6

output

  This circuit debounces a mercury switch in motion. Its output indicates the present status of the switch (dominantly open or closed). Debouncing is accomplished using a capacitor (Cl) voltage applied to the input of a transistor switch, Q3. When the capacitor voltage exceeds a threshold value, the transistor switch conducts. Both charging and discharging functions of the capacitor are employed.

The circuit is particularly suited to equipment having a mercury switch that is used with movement for example

where a user is walking or running. The mercury switch exhibits erratic contacting with motion. During running, alternate open and closure contacting occurs as tiequently as every 2-4 milliseconds with closure durationb as long as 200ms and open durations as brief as 2 milliseconds. To avoid accumulating charge during closures, a discharger having a Time Constant of x l/lOth of a millisecond is employed during openings. This will reset the charge vol- tage to zero if not a legitimate sustained closure. Charge time constant is 2 seconds.

  A latch state, Q2, provides the circuit the ability to maintain the output state once the circuit switches. Q2 disables the discharger Ql.

  To reset the circuit, the mercury switch is uprighted for P 1 second. This allows the capacitor voltage to dis- charge via R2 and fall below the thres...