Hi gryd3 the timer has arrived I think it's what we are looking for - Marks dog door
We can make this work.
The output is a single pole, double throw relay.. so it has a common pin, a normally closed and normally open pin.
I do not see a 'trigger' input anywhere on that device though which has me a tad concerned... it almost seems like the timer 'starts' when you provide power to it, and when the timer is up the relay goes back to neutral.
If this is the case, we can make the timer-relay power itself, so you can trigger it with a momentary push-button
I would also suggest the additional following parts:
- Two more relays. Just simple Single-Pole, Double-Throw relays that you can get at an automotive store, hobby store etc... 12V, and considering your actuator takes up to 3A, I'd find a relay sized at least 5A for this application.
(These relays will be used in a type of H-bridge that will allow the motor to reverse... if you don't want these, you will need two 12V supplies... so that you can toggle the -12V supply to the actuator with your timer relay. I recommend the additional pair of relays)
- Two normally closed, momentary push-buttons (Or microswitches) for the external limit switches. (If the actuator has two built-in, these will not be needed. You may only need one of these if you wish to use the built-in limit switch. Please confirm the use of the built-in switch first!)
- One normally open momentary push-button for the 'Door Open' trigger.
- *Optional but recommended, One normally closed momentary puch-button for the 'Door Close' over-ride.
Current plan:
The timer+relay combo will be wired so that the output of it's built-in relay will also provide power to itself. The momentary 'Open' button will cause the timer+relay combo to start and 'latch' on allowing you to release the button and the timer will continue on it's own. At the end of the timer duration the relay will return to the neutral position disconnecting power to it's timer circuit.
The 'Close' over-ride button will simply disconnect power from the relay+timer forcing it off sooner than the timer.
From here, we also connect a limit switch to each of the NC and NO outputs of the timer+relay combo. These switches will interrupt the signal from the timer if the door travels too far. ( Or to the pre-set position you would like to have )
These limit switches will then connect to their own relay.
The additional two relays will be wired such that when the timer is 'on' the relays will provide forward current opening the door. (until the limit switch is pressed, then the output will be neutral) . When the timer is off, the additional relays will provide reverse current to the actuator until the 'closed' limit switch is depressed.
This setup will allow you to use almost any device to open/close the door. A DC motor with a string, an actuator, etc... the H-bridge and limit switches will be quite robust and will also allow you to custom set the exact close and open position of the door simply by moving the limit switches.
Additional safety devices can be added and connected in series with the limit switches if you want to prevent the door from closing while something is in the door-way for example... a simple optical break-beam sensor can be installed and added on with no additional hardware. The switches and sensors will also be controlling a relay which is low-current as opposed to directly controlling the 3A actuator.
Anyway. Let me know what you think, and please confirm the exact behaviour of the motor and actuator to make sure this plan will work. (I'll draw a diagram shortly thereafter)
