From: Skenny@highstream.invalid   
      
   coetzee.evert@gmail.com wrote:   
   > Hi   
   >   
   > Yes please draw away. I finally found the LATCH keyword on wikipedia   
   > (should have started my search there).   
   >   
   > Won't a normal latch relay to it. Input button to start it, and then   
   > use the motor to physically trigger the reset when one revolution is   
   > completed.   
   >   
   Yes, that should work too.   
   Are you going to use a limit switch that will activate at the end of the   
   revolution?   
   The only problem I could see with using a latch relay would be that you   
   would have to use a normally open limit, which is closed when motor   
   reaches home position.   
   The relay will have the reset coil energized by the limit switch when   
   the motor is at rest, at home.   
   This may prevent you from latching the relay with the switch.   
   I guess you just need to make sure the reset doesnt overide the set on   
   the relay.   
   Also make sure the reset coil is rated for continious duty, so it doesnt   
   get hot while motor is at home position.   
   There are several ways you can do this. If the motor is DC, you can use   
   a SCR to fire on until the limit switch opens the circuit. You may have   
   to use a resistor in parallel with the motor to keep the SCR from   
   turning off when the motor brushes break the current flow.   
   If the motor is AC, for simplicity purposes I would just use a relay.   
   Does the pushbutton really need to be a one shot?   
   If you hold the pushbutton, do you still want the motor to stop at home,   
   having to release the button and re-press it to start the motor again?   
   Or do you want the motor to run continiuosly while the button is pressed?   
   Is the control voltage AC or DC? Is it the same as the supply for the motor?   
   Does the motor "stop on a dime", or will it coast when the power is   
   turned off?   
   These are simple basics that you will need to know before designing any   
   kind of control for this.   
      
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