Astable multivibrator d.c. bell

Claim 1

An astable multivibrator driven D.C. bell having a housing, a gong supported by the housing and a solenoid actuated striker assembly for striking said gong wherein the improvement comprises: a. an asymmetric free-running multivibrator which generates a frequency comparable to the natural frequency of the striker assembly for periodically actuating said solenoid actuated striker assembly and including: 1. first and second timing means including first and second capacitors, respectively, and wherein said first and second timing means have different timing values effective when activated for controlling the periods of energization and deenergization, respectively, of the solenoid of said solenoid actuated striker assembly so that the period of deenergization is always greater than the period of energization, 2. first and second transistors governed by the timing means for alternately activating the first and second timing means, 3. one terminal of said first and second capacitors of the first and second timing means being connected to the base of the first and second transistors, respectively, through individual diodes and having the other terminal of said first and second capacitors connected to the collectors of the second and first transistors, respectively, and wherein said diodes are poled for protecting said transistors against an excessive reverse bias, and b. driver circuit means including a third transistor which is controlled jointly by the timing means and the first and second transistors for delivering an output to the solenoid during the time interval when the first timing means is active, c. whereby the solenoid is energized for less than 50 percent of the duty cycle time for each actuation of the striker assembly when it is actuated at a frequency comparable to the natural frequeNcy of the striker assembly.