Fan pulse alarm using two stage comparator for speed detection

A fan slowdown indicator circuit, comprising:

• a first stage comparator including a pulse detector which detects a level of pulses from a fan, wherein said first stage comparator monitors back pulses of a turning DC motor of the fan using a pulsed isolation resistor, an input AC coupling capacitor and a pulse detector comparator;
• and
• a second stage comparator which sets the pulse from the fan at which an indicator indicates a slow pulse rate of the fan and which actuates the indicator, wherein said second stage comparator causes the indicator to have an indicator signal whose size is inversely proportional to the speed of the fan.

A fan slowdown indicator circuit, comprising:

• a first stage comparator including a pulse detector for detecting a level of pulses from a fan, wherein said first stage comparator monitors back pulses of a turning DC motor of a fan using a pulsed isolation resistor, an input AC coupling capacitor and a pulse detector comparator;
• and
• a second stage comparator including setting means for setting the pulse from the fan at which an indicator indicates a slow pulse rate of the fan and which actuates the indicator.

A fan slowdown indicator circuit, comprising:

• a first stage comparator including a pulse detector for detecting a level of pulses from a fan;
• and
• a second stage comparator including setting means for setting the pulse from the fan at which an indicator indicates a slow pulse rate of the fan and which actuates the indicator, wherein said second stage comparator causes the indicator to have an indicator signal whose size is inversely proportional to the speed of the fan.

A fan slowdown indicator circuit, comprising:

• a first stage comparator including a pulse detector for detecting a level of pulses from a fan, wherein said first stage comparator AC couples pulses from the fan and then amplifies them;
• and
• a second stage comparator including setting means for setting the pulse from the fan at which an indicator indicates a slow pulse rate of the fan and for actuating the indicator.