Look at the relay diagram again. In the rest state (SW1 open), both sides of the motor are grounded. Note that K1 is an impulse relay, and there is no standard schematic symbol for this critter. Each time it is actuated, it changes state and latches there even when power is removed. When the button is pressed again, K1 changes to the other state and latches there. Each time SW1 is pressed, K1 changes state and energizes one of the two motor relays, whichever one was not energized on the previous button press.

As noted, K1 acts as a toggle flipfllop. with the added feature that it does not require any power to retain its last state. Alternately, each motor relay is activated as long as SW1 is pressed, then returns its side of the motor to GND when SW1 is released.

ak

\Perhaps it is just the symbol that mislead me. It looks like the contacts of that first relay only have power when the pushbutton is pressed.

 

True. But the symbol does not accurately capture that the relay can be parked with either output contact closed. The first relay's contacts steer power to the other two relay coils, not the motor. That is why they are supplied by the switch; this meets one of the requirements in post #1.

 

True. But the symbol does not accurately capture that the relay can be parked with either output contact closed. The first relay's contacts steer power to the other two relay coils, not the motor. That is why they are supplied by the switch; this meets one of the requirements in post #1.

Then should the common contact of that relay go to +V and not the switch?

 

Hi Crutschow, I like it, but I need to buy parts to test it in on my breadboard. What app are you using for your similution, I could not find an file association for .asc files.

Thanks,

Majer3rd

 

Hi Crutschow, I like it, but I need to buy parts to test it in on my breadboard. What app are you using for your similution, I could not find an file association for .asc files.

I use LTspice, a free download from Linear Technology.
It's one of the best free Spice simulators available and used by several on these forums.

 

Then should the common contact of that relay go to +V and not the switch?

The common contact goes to V+ through the switch because one of the requirements is that the motor is energized as long as the switch is held, and "relaxes" when the switch is released. Running the relay coil power through the switch rather than the motor power lets the two motor relays act as power amplifiers.

ak