This isn’t a bad project to illustrate the finer points of design.
W can start out with simple requirements aside from the mechanical one and assume the simplest case:
1. A power source
2. A switch that is closed when the door is closed
3. A LED for each door
We know that this has to be a class II system, so power has to be limited (100 W or so). Voltages have to less than 24 VAC/DC to not have to use conduit etc.
LED’s can operate on AC or DC with additional components. There are inefficiences with using a DC regulated power supply. You can get 4W 120 V switching power supplies. An isolated supply needs to be used for safety.
One could consider the possibility of using a Bi-color LED to indicate OPEN/Closed based on color. Red- OPEN, Green – Closed. Green being associated with OK rather than it’s safe to enter the garage. One could decide that a green LED for the door is closed is an OK color.
Wiring: Doorbell, CAT3 or CAT5 (Ethernet cable) or quad telephone wiring would probably be appropriate. If this were alarm wiring then Red Teflon fire cable would be appropriate. Plenum rated wiring, would not likely have to be used, but wire entry may have to be sealed if it has to penetrate a fire wall of the home. Solid is best used within the walls. It’s easier to fish and won’t look sloppy when tacked on the ceiling.
If you use solid wire, you have to typically transition from solid to stranded in some places and provide a mechanism of strain reliefing the connections.
The LED’s: You can buy them in fixed voltages and with aestic looks or you cab use a clip like mount for standard LED’s. Typical LED’s used for this application drop about 2.1 V and the design createria is to usually operate at 20 mA.
A standard blank outlet plate can be drilled and dry transfer lettering be applied to give a very professional appearance.
If you use a low voltage box, there is typically no way to strain relief the wiring, so I’m advocating a typical electrical box or a low voltage box with a cord type strain relief. An underwriter’s knot and a grommet may suffice for a strain relief mechanism.
There needs to be a way to strain relief the wires to the LED. One way is to use a bezel type LED and place a small piece of bent metal behind it so that the wires to the LED can be strain reliefed. Stranded wiring, matching the colors of the wire used or even the polarity of the LED such as RED and Green which are quad shield colors. Small wirenuts can be used to make the connectons. Personally, I like DIN terminals with wire protectors. These are typically hard to find and may have long lead times.
At the garage door, you may or may not have to provide signal conditioning, but we are assuming not, since I have assumed a simple switch. So a box of some sort needs to make the transition from the garage door switch to the premise wiring. Agin, this could be a standard electrical box with grommets or a real cord connector. Cord connectors can be had for various internal range of diameters and use standard electrical conduit fittings. They can be had in plastic and Aluminum. Again, wire nuts can be used to make the connections. If the difference of wire gauges is large, then other options could be considered. Another way is to just mount a plastic box with a metal cover nearby and use grommets. Some of the wires could be strain reliefed by say a wire staple.
It’s best to run all the wires as a home run to the controller which needs to be near a power source. Wires can be run through joists and holes drilled in the center of the joists. Cable clips can be used to tack the wires in place, For home wiring, I tend to use expensive RIP ties, because wires can be easily added or subtracted from the route. You don’t want to pinch the wire and sharp bends should be avoided.
The location could be the ceiling near the light since that has a power source, but troubleshooting might be awkward there. Let’s assume that location for now.
A box has to be picked that will fit and this is where you can end up with troubleshooting issues, A professional approach might use disconnectable terminal strips on a PC board or use terminal strips and a header connecter to the main board.
We might chose a PC board system or we could use DIN rail and DIN terminals. The latter would increase the cost significanty, let’s go with pluggable terminals. We can change the size to avoid the wrong insertion. In our simple case.
5 terminals for the sensor (Run a 4 conductor cable).
Possible sensor power, sensor gnd, sensor signal, sensor GND
In our simple case, 2 conductors would be used
Two such connectors.
4 terminals for the LED (2 such connectors)
Lots of options here. Let’s assume one 4 conductor cable to LED’s
3 terminals for power.
One might become a shield
Assume a wall Wart
You have to make a decision as to whether to allow swapping of LED’s and sensors. In any even, they can be swapped with the screws on the connectors and it would be easy with the right pluggable headers.
When creating the contents of the box I’d probably go for a 12 V unregulated wall wart.
Now, I might change the design slightly and put a 1N4001 diode in series with the LED for reverse polarity protection, Soldered and heat shrinked at the box, so if I hook the LED u backwards nothing bad happens.
The LM334 is a nice maximum 10 mA current regulator. If 10 mA is enough for the LED’s we could use this. I have used it and I like the method. We can use other techniques too.
Using a 5V or 12 V power regulated supply poses other issues. Without some sort of regulation or transient suppression, the design may not be reliable, so the design should have a fuse for the power and at a minmum have transient protection. The fuse could be internal or external. You could place a power LED on the box to indicate power. The fuse could be external or internal. Assume internal.
So, the PC board contains a few components (a current limiter, transient protection, a fuse and essentially the point to point wiring, so that the system is clean and easy to troubleshoot. Standoffs would be required to mount the board.
This illustrates the design process and some of the tradeoffs. I like systems that are reliable and easy to troubleshoot. At work, in a research environment, I liked things to be modular and reuseable,
This illustrates that a very simple project has lots of hidden costs. Anyone building projects realized that the power supply, real estate (PC board) and the case contributes largely to the costs. Connectors, while a necessary evil contributes negatively to reliability
Here is a datasheet for the LM334.
https://www.electro-tech-online.com/custompdfs/2011/01/LM334.pdf So your only real components are: The current regulator, 2 resistors, a transient voltage protector, optional diodes for reverse polarity protection ( 2 for the LEDs and 1 for the power supply and a fuse)
I hope you find this info useful. Typical vendors are
Electronic Components Distributor | DigiKey Corp. | US Home Page,
www.jameco.com ,
Mouser Electronics - Electronic Component Distributor and
US - Electronic Components Distributor | Newark.com
The system is simple. It's just the details that kill you. If you don't have an electrical outlet nearby that just adds more expense.
The simple version is a switch, a regulated power supply, a resistor for each LED. I'll end with "If you don't have time to do it right, when will you have time to do it over". Now there is always the option of having someone do most of it for you. Say, make the main box and the LED plate.