# NO/NC AC Actuator

I'm looking to build some projector cases for a school gymnasium which is a high dust environment. I'm looking to create an enclosure with a solenoid/servo/actuator that will open the enclosure at the front when the projector is powered on (to allow projector light through) and then will close again, when power is disconnected.

What kind of motor would I need to open an enclosure door?

If I'm in the wrong spot, please tell me and I'll repost elsewhere. Thanks guys!

• A few more details required including mounting and power arrangements. (1) How are you going to manage heat generation inside the enclosures? (2) If these are digital projectors how will you ensure that the correct power-down sequence is observed before someone switches off the mains power remotely? (Normal digital projector power-down runs a cooling sequence so you can't just "pull the mains plug".) Pop all the information in your question rather than sprinkled through the comments. – Transistor Sep 23 '17 at 3:03
• A motorized sliding door is easy to design, once the door is designed properly to meet the requirements and the remote powered projector model is known. It could be designed and built for $50 or$1500 depending on your answers to the above and any additional requirements. – Tony Stewart Sunnyskyguy EE75 Sep 23 '17 at 12:46
• Someone with design skills might be able to motorize a door with a gear servo motor or stepper motor belt drive for even less, if the lowest Nt-cm door design was defined for torque. Such as a thin panel on rollers with an end switch for logic from a cheap remote control toy. In other words your door slide design and ingenuity determines the range of costs for a remote or automated door slide but more details are needed. And design time is money and I'm not cheap but here I am free. – Tony Stewart Sunnyskyguy EE75 Sep 23 '17 at 13:03

This might be fairly easy to do.

1) Monitor the current into the projector. This is most easily done by using a clamp-type current sensor clipped over either the Line or Neutral conductor going into the projector. Have your local electrician install the sensor inside the junction box that holds the AC power receptacle that the projector plugs into.

One such device is available from Seeed Studio Non-Invasive Current Sensor 20A Note the triple "E" in the company name.

The output from the sensor is an AC current that is proportional to the current sensed. You will convert that current to a voltage for easier detection.

There are a variety of circuit types available that can detect when a voltage is above or below a certain threshold. The output of this circuit will then control the actuator that opens and closes the projector door.

The reason this is easy is that the idle current of the projector is much, much lower than when the lamp is illuminated. Open the door when the current goes above the threshold. Close the door some time period after the current drops down below the threshold.

If I were doing this project, parts count would be minimal. The current sensor, a few passive components, an 8-pin PIC microcontroller, the output relay, a tiny power supply for the PIC.

If you were really clever, you might be able to power the PIC with the signal from the current sensor.

Note that the only reason I would use a PIC microcontroller is for the timer that keeps the door open after the lamp goes out. Easier to do that timer with a few lines of code than all of the components needed for a timer or counter chip.