One way would be to use a phase locked loop locked to the normal tooth frequency. That would generate a clock edge that could be used to sample the missing tooth... You could do this in software inside a uController, too, i.e. compare the previous period between the two last teeth to a running average period.
One way would be to use a phase locked loop locked to the normal tooth frequency. That would generate a clock edge that could be used to sample the missing tooth... You could do this in software inside a uController, too, i.e. compare the previous period between the two last teeth to a running average period.
One way would be to use a phase locked loop locked to the normal tooth frequency. That would generate a clock edge that could be used to sample the missing tooth... You could do this in software inside a uController, too, i.e. compare the previous period between the two last teeth to a running average period.
Such a missing pulse detector will only work for a fixed frequency, since the 555 time must be set to be slightly longer than the period between pulses. It won't work for a range of speeds as the OP desires.
Use two magnetic transducers so that when the gear is ok their output is identical. If one tooth is missing then at some point the output of the sensors will be different.