I'm trying to make this circuit work but having no luck. I'm using a anemometer for the input which gives 1 pulse per revolution. I'm trying to get the alarm to sound when reaching approximately 70 MPH. I'm not getting an alarm at any range on the speed adjust which is 26.6 - 82.8 MPH. I am also trying to find a way that once the alarm is sounded, it will stay on until it is reset. I would be thankful for someone's help on this circuit.

 

You'll need to actually provide trigger pulses in addition to adjusting Rv1.

For an alarm which stays on until reset, try replacing the second half of the 4538 with a resetable flip-flop.

 

Could you explain adding new trigger pulses and what flip-flop I might need? Also, how can I put this together? Thanks.

 

Your circuit does not show the anemometer mechanism. If the construction allows it, mounting a small bar magnet on the bottom of the shaft so it is mechanically balanced will lets the poles rotate past a reed switch mounted so the magnet ends just miss contact with the glass body. You can see the reeds come in contact and release to adjust the positioning.

The reed switch terminals connect to the circuit at the left side. One foes to circuit ground and the other to the junction of R3 & 5. When the reeds close, it will trigger the first one-shot.

The alarm latching can be done with a small double-pole relay. One set of contacts passes current through the alarm, and the other makes a path for current through the coil, so it will latch on.

The alarm will be more reliable is you use a 9 VDC wall transformer in place of the battery. It will let you have more power for a louder alarm

 

Check page 14 "Overspeed Latch" in attached:

BTW -- you should be able to get a reluctor and sensor out of a distributor at a junk yard.

 

The circuit input to the left is a magnetic reed switch producing 1 pulse per revolution. After spinning the anemometer, I am getting no signal to the alarm. I am trying to find out why? Will the same circuit work with some changes? Thank you for helping.

 

How many anemometer revolutions per second are required to simulate 27 mph?

 

I didn't design this circuit, I am just building it from the schematic. The person who designed it said it would work, but having no luck getting it to work. I would appreciate all the help.