Control unit and method of making the same

Claim 1

In a control system comprising a high energy control circuit means having an output relay driver transistor, manually operated means for initiating the operation of said high energy control circuit means, microcomputer means for operating the high energy control circuit means after said manually operated means has initiated the operation thereof, and supervisory circuit means for detecting failure of said system and disabling said high energy control circuit means if said system is not operating in a normal mode thereof, said supervisory circuit means having means requiring the manual operation of said manually operated means before permitting power to reach said high energy control circuit means whereby said high energy control circuit means is disabled unless said manual operation of said manually operated means has taken place and said system is operating in said normal mode thereof, said supervisory circuit means having a supervisory transistor therein that is in series with said relay driver transistor and that must be switched on to enable said relay driver transistor, the improvement wherein said supervisory circuit means has capacitor therein for sustaining the on condition of said supervisory transistor, said manually operated means comprising momentary means for initially charging said capacitor and switching on said supervisory transistor when said manually operated means has been manually and momentarily operated to initiate the operation of said high energy control circuit means, said system having means for continuing the charging of said capacitor only after the initial manual and momentary operation of said manually operated means has initially charged said capacitor and if said system is operating in a normal mode thereof.