Can someone help me understand how this circuit works (attached)? I understand what all the symbols are except the triangle at the bottom. Is that a ground? Assuming it is, here's what I think I understand so far:
1. the 12v relay turns the motor on and off
2. when the relay is energized, it closes the "normally open contact" to the motor, so current flows from +12 VDC through the wire at the right of the diagram
3. the 2N4401 is a NPN transistor, meaning (I think) no current can flow from the collector to the emiter unless there's enough current applied to the base.
4. the other transistor is PNP. I assume it works the same way, but I don't understand why this is used rather than a NPN.
5. So, I think when the wiper switch is on, the only complete circuit at first is via the 47k resistor on the left.
6. Current via the 47k resistor goes to the base of the PNP transistor and turns it on, allowing current traveling via the 10k resistor to go from the collector to the emiter. The amount of current from C to E is controlled by the 500k potentiometer.
7. Once the PNP transistor is turned on, current can flow to the base of the NPN transistor and the capacitor. I don't understand what that arrangement does. I know the potentiometer controls the duration of the on/off interval for the wiper motor, but I can't figure out how.
Can someone walk me through this circuit? - Thanks
1. the 12v relay turns the motor on and off
2. when the relay is energized, it closes the "normally open contact" to the motor, so current flows from +12 VDC through the wire at the right of the diagram
3. the 2N4401 is a NPN transistor, meaning (I think) no current can flow from the collector to the emiter unless there's enough current applied to the base.
4. the other transistor is PNP. I assume it works the same way, but I don't understand why this is used rather than a NPN.
5. So, I think when the wiper switch is on, the only complete circuit at first is via the 47k resistor on the left.
6. Current via the 47k resistor goes to the base of the PNP transistor and turns it on, allowing current traveling via the 10k resistor to go from the collector to the emiter. The amount of current from C to E is controlled by the 500k potentiometer.
7. Once the PNP transistor is turned on, current can flow to the base of the NPN transistor and the capacitor. I don't understand what that arrangement does. I know the potentiometer controls the duration of the on/off interval for the wiper motor, but I can't figure out how.
Can someone walk me through this circuit? - Thanks