[Amps] 8877 blower requirement...TXN ! Now..Airflow sensing ?

[Peter Chadwick]

One simple method is a small fan, free to rotate in the air stream. An LED- opto transistor arrangement then gives a series of pulses when the fan is arranged to interrupt the light beam, and a re-triggerable monostable - 74123 - gives a logic ouput that reverses when the air and fan stop. A bit of friction on the fan spindle and itr can detect low velocity air, too. Probably easier than a sensitive microswitch and an air bleed of one sort or another.
73
Peter G3RZP.