I designed these boxes to be interchangeable. Any lid will fit into any box. I have 1, 2, 3, and 4 chamber boxes. Only 1 and 2 are in the picture.
And 6 different lids: blank, HC-SR04, PIR, LM2596, Arduino Nano, and relay.
You will probably need a couple of drops of super glue to hold the PIR in place. All the other components slide into place and stay put.
I have 2 different dimensions for relays. On one of them the circuit board is 46mm long X 17mm wide. This one will fit into the lid.
The other relay I have measures 43.5mm long X 26.5mm wide. I made a different box for this size. It is a little too wide for my universal boxes. It will hang upside down in the box.
Here is a round housing for the HC-SR04. I tried to make it look industrial.
Mount my arduino boxes to a 35mm din rail
A few more lids and stuff are here: