Thinking outside the metal (steel) mailbox

A contact sensor inside my steel mailbox of forty years would not work. Even though the bridge is a direct line of sight at about 35’. I worked up several designs for keeping the contact sensor external while actuating it with a linkage attached to the mailbox door. This was doable but I wanted something simpler. WARRANTY VIOLATION AHEAD! I decided to modify the sensor so it could be mounted inside the mailbox while its antenna would be outside the mailbox. This was done by un-soldering the original antenna from the circuit board and re-soldering it to the end of a 25” long extension wire. The other end of the extension wire passed through a hole made in the side of the sensor case and soldered to the old antenna attachment. Signal strength before the project was 2 bars and after the modification 2 bars.
The first two pictures show the front and back side of the circuit board. With some labeling.

The third picture show the antenna connected to the end of the extension wire.

The fourth picture shows details of connecting the extension wire to the circuit board. I explain here that the detail put forth is better than what was actually done. It was difficult to get the board back in the case. The shown detail should be much easier to work with.

The Fifth picture shows the route I would use for the extension wire in and outside the mailbox. The 3/16” slotted hole in the back of mailbox a gentle entry and curving of the extension wire.

The last picture shows the finished installation. Later I will put better outside tape and paint it with a matching paint. The sensor unit and magnet installations may have to hardened later. It works very well.

This approach of placing the antenna remote from the sensor unit may have applications with steel doors.
Victor Maletic

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Sorry pictures three and four should be swapped.

Nice write up . :+1:
One Thing though for everyone putting sensors in their mailbox, if The mail carrier Stuffs a package in there and knocks Your sensor off , Don’t get upset It’s not their fault

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Absolutely correct. That is why I will be hardening up the sensor and magnet mounts. Probably with a plastic surround. I’ll send a picture soon.
Victor Maleic

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Sounds good .
You have come up with some good ideas I have seen on here

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Thankyou for the acknowledgment. I have hardened up the mailbox contact sensor installation.
See photos below.
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Victor Maletic

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I see one photo did not load. Here it is.

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Wouldn’t that change the loading and frequency?
Surely you want to ground your extension screen so the only active part is the antenna itself?

Genius!!! I got contact sensors yesterday. I think this modification with the PVC may work work better for placing the sensors on the garage doors since the metal always causes interference.

That’s one of the reasons I used a motion sensor in the very back of the mailbox instead. Very unlikely to get knocked off. Working great for me.

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Great work! I wonder if you actually need to solder the original antenna on to the end of the extension wire? Perhaps the wire acts like an antenna? Or maybe a better antenna could be utilized if range is any kind of issue.

I agree that it is unlikely to get knocked off, but a package bashing is not so unlikely, perhaps a 1" thick styrofoam donut or something similar could limit that exposure.
Victor Maletic

Whenever I first have to change the battery, I’ll probably make a holder for it so I don’t have to keep changing the adhesive.

A styrofoam donut with the hole sized to create a snug fit with the motion sensor’s corners would be a mount and a buffer. A small piece of tape around the back and sides could serve as a pull tab.
Victor Maletic

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The wire does act like an antenna, needs to be the right length though otherwise it’ll be tuned to a different frequency

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I’m sure there is an affect on the contact sensor system due to the antenna extension. Probably not a frequency change because I get notices when the mail box is opened and closed, no other notices.
My nephew did the calculations for what shielded wire would work. When he gets back into town I will ask him for a more detailed explanation and send it on to you.

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I beleive the contact sensor antenna has to be soldered on to the end of the extension. The extension lenght needed is 20" to 25" and would respond to too low of a frequency for contact sensor. As I understand it the purpose of the shielding on the extension is to prevent the extension wire from acting like an antenna,
I’m sure there is an affect on the contact sensor system due to the antenna extension. Probably not a frequency change because I get notices when the mail box is opened and closed, no other notices.
My nephew did the calculations for what shielded wire would work. When he gets back into town I will ask him for a more detailed explanation and send it on to you.

That’s true if the screen (shielding) is connected, in your diagram you have only connected the core

The frequency of the device would be the same but the tuning of the antenna would be off, making it a lot less efficient and possibly damaging the the circuit due to voltage reflections

Easy fix though either connect the screen to ground (bat-) which will stop the wire from being an active element or convert it into a monopole, with a screen you can also make a dipole

What’s the max range with and without modification of the contact sensor?

Same! Motion sensor in the back. I’m only getting notifications about 30% of the time and believe I have the same problem. Going to try this