Making a Smaller Passive Key Fob

[mustang1]

Thanks for this response. I guess you are right that I will probably not have the skill to desolder the buttons. And - even if I did - they might be more complex than just closing a circuit.
...

you should able to de-solder the buttons and that will leave an open circuit.

heat shrink tubing is a cleaner solution than electrical tape.

for both of these, you will need proper equipment, which may run $50-100.

And maybe be prepared to buy 1 or 2 more key fobs if they get messed up. Or better yet, experiment on some junk electronics.

does your wallet bend at all? That could be a problem

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[Beef]

Can you post a pic of the other side of the PCB??

 

[Ground Speed]

I've thought about building a flat 3d printable case for a place like Shapeways, I just haven't taken the time to reverse engineer the fob and haven't built up the courage to disassemble one of my keyfobs for the exact layout and dimensions of the PCB.

There are a few challenges going this route, but nothing that would prevent it from being a viable alternative to the NFL footballs Ford used as a size goal for our key fobs.

There may even be a version or two on Shapeways already. My version, as you said, would aim to be as flat as possible, but I'd have to experiment with the overall shape, design it to accommodate being assembled and taken apart to allow for battery replacement, and perhaps most important of all I'd have to narrow down the material choices to account for durability, protection of the inner PCB, etc. I'd also probably disable the panic button but keep functionality in the rest - another challenge of design.

Either way I'm subbing this thread. Thanks for the write up, I'll be interested to see how your version turns out.

 

[Libertas]

UPDATE: Wrapped in Tape and Comparison

I still have to find a way to omit the buttons (havent had a chance to go to the store to buy nylon washers or to try to desolder)

But I did a quick and dirty tape wrap to hold it together for now.

Here is the battery side wrapped in tape:

Here is the button side wrapped in tape:

Here is a side view with metric ruler for thickness view:

Here it is next to my office door key fob that has been living in my wallet for over a decade and which gave me the idea for this:

Here is a thickness comparison with my office key fob:

I used it this morning to drive to work and I have to say, even in the front pocket of my slacks (because putting it in my wallet now would push buttons), it is a huge improvement. I don't even notice it is there.

 

[cbrookre]

Thanks for this response. I guess you are right that I will probably not have the skill to desolder the buttons. And - even if I did - they might be more complex than just closing a circuit.

I am guessing that the antenna is the line around the perimeter where the key hole is. Everything else seems functional, so no real way to make it smaller. Wish I could get slimmer.

As for a case, this will live in my wallet, so I really don't care what it looks like and a good electrical tape wrap is probably the thinnest way to go.

I'll head to the hardware store to look for nylon washers this weekend and update with a photo and status.

With all of the cars out there that have push button start and touch door handles for lock/unlock, I'm surprised there is not a more elegant solution out there.

You are right that the PCB cannot be cut down, but taking off the buttons would be really easy. They are surface mount, so really heat them up with a solder gun (all on one side) and gently pull up with needle nose pliers. I also have done this a number of times and it is very easy to do. The likelihood that there would be any adverse affects would be very small (ie, they would have to have wired up the buttons in a very unconventional way). But other than that, there is no real way to cut down the x and y dimensions without redesigning the board.

 

[PJR202]

Thanks for this response. I guess you are right that I will probably not have the skill to desolder the buttons. And - even if I did - they might be more complex than just closing a circuit.

Didn't mean to deflate your idea. You could get a fine tipped soldering iron and learn to solder fairly quickly, but that is VERY small circuitry and very delicate paths embedded. Those paths can heat up and curl up if you aren't careful...or even if you ARE careful..lol

I have a Tacoma with the overhead temperature/direction console. They're well known for dying because of a poor calculation in a couple resistors. Several months back, I went in and replaced the two itty bitty flat resistors that fail (due to heat) with a couple sets of three regular ones stacked in parallel. It was beyond tedious for me because you have to heat the solder without frying your component or melting holes into the board, and you have to wick or suck away the solder while it's hot. It's very frustrating and I was dropping F bombs and wanted to kill something by the time I got the flat ones removed. Your board (and components) is much smaller than the one I worked on. It was probably assembled and soldered by a robot. Robots don't cuss. They might kill though..who knows?

 

[Chameleon]

I've thought about building a flat 3d printable case for a place like Shapeways, I just haven't taken the time to reverse engineer the fob and haven't built up the courage to disassemble one of my keyfobs for the exact layout and dimensions of the PCB.

There are a few challenges going this route, but nothing that would prevent it from being a viable alternative to the NFL footballs Ford used as a size goal for our key fobs.

There may even be a version or two on Shapeways already. My version, as you said, would aim to be as flat as possible, but I'd have to experiment with the overall shape, design it to accommodate being assembled and taken apart to allow for battery replacement, and perhaps most important of all I'd have to narrow down the material choices to account for durability, protection of the inner PCB, etc. I'd also probably disable the panic button but keep functionality in the rest - another challenge of design.

Either way I'm subbing this thread. Thanks for the write up, I'll be interested to see how your version turns out.

Haha! Well said.

 

[ninjawasaki]

I'm not an electronics guru by any step of the means, but it would be cool to outfit these fobs with capacitive touch type buttons to help with the pocket button pushes. It might even help with the form factor as well. Hell it may not even be possible haha.

Very cool project you took on though!

 

[Harebear72]

Interested

 

[STANGBOY]

Dang thanks man! I might do this this weekend

 

[Libertas]

FINISHED! SUCCESS!!!

Forget about soldering. Forget about nylon washers. I just went for it with a pair of needle nose pliers. Gripped the whole button assembly square head on and gave the smallest of pulls. Came right off the board. Could not have been easier. They are barely stuck on at all. Used the needle nose pliers to just knock down any remaining pointy stuff (there wasn't much). Reassembled the battery, etc as before, and . . .

Ta-Da!

It worked perfectly. No buttons. Just a passive key fob that fits in my wallet. As long as I have my wallet on me (and I always have my wallet on me) I can use my car.

Done. End of story. It's a really simple $50 mod.

EDIT: Here is a better photo of how the battery is hooked up (before I applied the tape)

 

[Chameleon]

Nice!!

 

[EasyBeingGreen]

Predicting the next thread title by Libertas...

"Help! I left my wallet in the car and someone drove away with both!"

 

[mustang1]

better keep a fat wallet, or the wallet may flex and the fob radio will stop working at an inconvenient time.

 

[Kudarat]

cool. just keep an extra battery just incase it goes dead to avoid lockout. ;)

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