| 摘要 |
A tachometer signal conditioning circuit (20) includes a timer circuit (48) responsive to ignition pulses from the primary lead (28) of an internal combustion engine ignition coil (26), and outputting a timing pulse terminating after a given time delay interval during which RFI, EMI and other transients on the primary lead (28) are ignored. A one shot monostable multivibrator circuit (56) responds to the trailing edge of the timing pulse and outputs a trigger pulse of given duration. A switch circuit (66) is connected to the battery circuit (22) and is turned on by the leading edge of the trigger pulse and turned off by the trailing edge of the trigger pulse, all before the next ignition pulse. The switch circuit (66) has a node (80) providing an input for a standard low voltage tachometer (82). Conductive and nonconductive states of the switch circuit (66) change the battery circuit voltage at the node (80) at a frequency corresponding to the frequency of the ignition pulses.
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