Perhaps not so mysterious a design. Your tachometer uses a pulse per unit time to voltage conversion no digital stuff here nor D-A conversion. So if the transfer function of pulses per unit time to voltage is known and the desired range of ppt is known then the range of voltage is known. A comparator circuit can give you a measure of whether the voltage is within the specified range. If below then you have a signal that indicates engine speed too low. If above then engine speed too high. Detailed design left to David B or those with that sort of "bent". Pensioner Tau Beta Pi (bent), Eta Kappa Nu, Phi Kappa Phi in EE/CS, O so long ago. |
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