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Sliding door control modification...

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tommyelliott59

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I have sliding metal doors which operate using push bottons (normally open 2 wire). They also operate with bumper strips (also normally open 2 wire) one on either side of the door. They open with a single press of the open push button or bumping into the vertical bumper strips down below. When the switches close they return 5 vdc back to the controller. Pretty simple. I've been asked to make a mod to prevent accidental opening. They asked for a double-click style actuation, wanting it to take two bumps of the bumper strips to open the door rather than only one. I imagine that a single accidental hit to the bumper strip would be forgotten after a couple of seconds so another accidental hit 30 seconds later would not make the door open. The double-click style bumps to the bumper strips would need to come close together.

The bumper strips are simply piggy-back connected with the open push buttons and the strips will be disconnected and only operate through the proposed mod, leaving the push buttons connected as before for single button presses to operate those.

24 vdc is readily available to power the modification, 5 vdc may also be available for use as well.;)
 
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That's definitely doable. Is this to allow someone in a wheelchair to operate the doors? You mention door opening; what about door closing?
Unless someone else jumps in first I'll design something. Watch this space.
 
Not for wheelchair access...

Hi Alec, Thanks for answering my query and looking into it.

The doors are on Operating Rooms. As they are, you press buttons once to open the doors. There are three button choices.

The top one opens the doors fully and leaves them open until you once again press the top button.

The next button down is for personnel entry and only opens the doors half way, holds for one second and then closes the doors.

The last button is for patient bed transfer in or out of the room. It opens the doors fully just as the top-most button does but only holds them open for about 18 seconds and then lets them close.

That covers the push-buttons. There are also (on the left and right sides) below the buttons and extending almost to the floor two black rubber bump-strips that are simple contact switches (normally open 2-wire like the push-buttons above). These bump-strips are connected across the same 2 wires of the Bed Transfer push-button. This factory connection I will need to disconnect and the modification will be wired between the bump-strip wires and the Bed Transfer push-button wires so the Bed Transfer push-buttons won't be affected and will still open the doors with only a single push of that button. Only the bump-strips will require a double hit to make the doors open. They don't want the doors to accidentally open during a surgery if someone comes by and hits a bump-strip with a cart, patient bed, or other mobile equipment.

Thanks again for your help.
 
Understood. Attached is a suggested circuit. Not knowing the input characteristics of your door controller I have assumed that a transistor rated to supply up to 200mA will suffice to switch 5V on to the controller input wire. It can be replaced by a FET or relay if required for a higher current.
The circuit operates from a 5V supply and uses two ICs: a CD4013 dual D-latch and a CD4011 quad NAND gate.
Both latches are wired as monostables. The first monostable (U1a) generates a ~0.9 sec pulse at its Q output in response to operation of a bumper switch and can't be retriggered within that period (thus overcoming switch bounce). The second (U1b) is triggered on the trailing edge of that pulse and generates a ~ 3 sec pulse at its Q output. This defines a 3 sec time window and if the bumper switch is operated again within that time window the second pulse from U1a enables the NAND gates (here wired in parallel, although strictly only one is necessary) to turn on transistor Q1 to switch 5V to the controller for ~0.9 secs. The Bed Transfer switch is connected in parallel with Q1. For purposes of simulation only, the controller is represented by a 1k load resistor.
The circuit timing is adaptable. R1/C1 set the U1a pulse width; R4/C2 set the window width.
After triggering of the time window monostable, a period of about twice the window width (i.e. about 6 secs) is advisable to allow the circuit to 'reset' to its quiescent state.
 
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Alec,

I'm a bit confused on the pinout for the CD4013. The schematic indicates PRE but I don't see this on the chip's pinout diagram, only set and reset pins. Would you clarify this for me? Thank you once again for your help, your work is excellent and very much appreciated!
 
In LTSpice-speak, PRE(set) = SET and CLR = RESET. Any other probs, give a shout.
BTW, my schematic doesn't show the customary power/chip supply decoupling caps (I'd suggest 100μF and 100nF).
 
what about using 4017 ?

Edit: i could further simplify it and posted final one, using 4017 and one OR gate (can be omitted too)

when its pressed once, the out put will slowly increase the reset voltage, if its hit second time before getting reset, it will give open command, if not hit again the system will get reset.
 
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I like that idea, but you would have to guarantee there was no switch bounce. In practice a train of bounce pulses could cause spurious door opening and leave the counter in an unknown state, so that the Q1 output would not then generate a reset ramp voltage.
 
Tommy:

Since this is an OR, I'm not sure you want to invest into a direct home made type design. Have you thought about using something like a SMART RELAY from Idec https://us.idec.com/Catalog/Product...DEC_SmartRelay&FamilyName=Programmable_Relays to do the interface?

Yep, it's overkill, but you can taylor the timeouts as you need them. You might even make the other switches cancel the timeouts. Everything becomes a little software.

You can download a simulator and they can be programed in a flow chart form or Ladder logic.

Your interface could be relays or I/O modules.

Just a thought?
 
I like that idea, but you would have to guarantee there was no switch bounce. In practice a train of bounce pulses could cause spurious door opening and leave the counter in an unknown state, so that the Q1 output would not then generate a reset ramp voltage.

Switch bounce can be prevented at input by simple RC filter. another improvement can be done to lock the output by connecting Q2 to CP1(enable input)
 
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