From: Skenny@highstream.invalid   
      
   Skenny wrote:   
   > 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.   
      
   Here is a drawing of the first circuit, which assumes the control   
   voltage is same as motor voltage, and it uses a regular relay, which   
   should be cheaper than a latch relay.   
   Motor runs continuously if button is held.   
   http://relaycircuits.blogspot.com/   
      
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