Write a program for an antitie down circuit that will disall

Write a program for an “anti–tie down circuit” that

will disallow a punch press solenoid from operat-
ing unless both hands are on the two palm start

buttons. Both buttons must be pressed at the same

time within 0.5 s. The circuit also will not allow the

operator to tie down one of the buttons and operate

the press with just one button. (Hint: Once either of

the buttons is pressed, begin timing 0.5 s. Then, if

both buttons are not pressed, prevent the press sole-
noid from operating.)

Modify the program for the control of traffi c lights

in two directions so that there is a 3-s period when

both directions will have their red lights illuminated.

Solution

Start 1 Timer (.5 sec)
---||---------------------------------------()-------


Start 1 Start 2 Timer (timing) Operate
---||----------||------------||-------------()-------


That should be all you would need to start it. Only way it operates is if one button is pressed which will start the timer, and within that half second while the timer is counting, both buttons would need to be pressed to operate.

As far as not tying one button down, you could just have a timeout function.


Start 1 Timer 2 (timeout)
---||-----------------------------------------------()-------


Start 2 Timer 3 (timeout)
---||-----------------------------------------------()-------


Timer 2 Disable
---||------------------------------------------------()------
|
Timer 3 |
---||-------|

The logic behind this is:-

Check for button 1 not pressed.
Check for button 2 not pressed.

If B1 and B2 not pressed, reset anti-tie-down logic

(both buttons need to be not pressed to reset the tie-down logic and allow the next activation.

Then to allow next cycle:

If button1 OR button 2 is pressed, start 0.5s timer
IF, while button 1 or button 2 is pressed,
AND during 0.5s timer
Then if other button (1 or 2) is pressed, activate punch press cycle.

After cycle, do not release anti-tie down until both buttons are not pressed.

As someone else said, always de-bounce the buttons. 0.1-0.15s should do it.

You can do this with ladder logic, in a state machine, or with parallel ladders.