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Quickie Teardown – ShopGuard Anti-Theft Tag

ShopGuard Anti-Theft Tag
ShopGuard Anti-Theft Tag

Everyone at some stage must have seen these EAS security tags in shops, usually attached to clothing with a steel pin. As some of this year’s presents had been left with the tags attached, I had to forcibly remove them before wrapping could commence.

Reverse Side
Reverse Side

These are just a plastic disc about 50mm in diameter, with an internal locking mechanism & RF tag inside.

RF Coil
RF Coil

After some careful attack with a saw around the glue seam, the tag comes apart into it’s halves. The RF coil & it’s ceramic capacitor can be seen wrapped around the outside of the tag. The capacitor in this case isn’t even epoxy dipped to save that extra 0.0001p on the manufacturing price. In the top centre is the pin locking mechanism, enclosed in a small plastic pill.

Lock Pill
Lock Pill

Popping off the back cap of the lock shows it’s internals.

Ball Bearing Lock Assembly
Ball Bearing Lock Assembly

The lock itself is very simple. The centre section, held in place by a spring, carries 3 small ball bearings. The outer metal frame of the lock is conical in shape.

When the pin is pushed into the tag, the conical shape of the lock chamber causes the ball bearings to grab onto it, helped by the action of the spring that pushes the ball bearing carrier further into the cone.
This also means that any attempt to force the mechanism causes it to lock tighter onto the pin.
In normal operation, removal is achieved by a strong magnet that pulls the ball bearing carrier back slightly against it’s spring, allowing the pin to disengage & be pulled out.

This design is incredibly simple & cheap to make, and gains it’s locking strength from friction alone.

I would consider the RF coil being around the outer edge of the device a bit of a security risk – a quick chop with a sharp pair of wire cutters would disable the tag’s alarm functionality instantly. Making the coil slightly smaller & keeping it out of reach of the edge of the tag would help in this regard.

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Electronic Lighter – eBay Freebie

With a recent order from a Chinese seller on eBay, this little gadget was included in the package as a freebie:

Electronic Lighter
Electronic Lighter

I’ve not smoked for a long time, so I’m not too sure what use I’m going to find for this device, but it’s an electronic lighter!

Pyromaniac Mode
Pyromaniac Mode

Pushing the slider forward reveals a red-hot heater, mounted in the plastic (!) frame.

Charging Mode
Charging Mode

Pushing the other way reveals a USB port to charge the internal battery.

Core Removed
Core Removed

A couple of screws releases the end cap from the cover & the entire core unit slides out. Like all Chinese toys it’s made of the cheapest plastic imaginable, not such a good thing when heat is involved.

Heating Element
Heating Element

The element itself is a simple coil of Nichrome wire, crimped to a pair of brass terminals. The base the heater & it’s terminals are mounted to is actually ceramic – the surround though that this ceramic pill clips into is just the same cheap plastic. Luckily, the element only remains on for a few seconds on each button push, there’s no way to keep it on & start an in-pocket fire, as far as I can see.

Main PCB
Main PCB

The main PCB clips out of the back of the core frame, the large pair of tinned pads on the left connect to the heater, the control IC has no numbering of any kind, but considering the behaviour of the device it’s most likely a standard eCig control IC.

LiPo Cell
LiPo Cell

The other side of the board has the USB port on the right, the Lithium Polymer cell in the centre, and the power button on the left. The cell itself also has no marking, but I’m guessing a couple hundred mAh from the physical size.

 

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Stock Baofeng Antenna Problems

Recently I’ve noticed my usual mobile rig, the Baofeng UV-5R, has had very poor receive, and non-existent transmit.

I did a power test on the radio, and confirmed it was still outputting it’s rated RF power. Trying another antenna proved that the radio was fine.

Time to tear down the antenna & see if it can be fixed!

Stock Antenna
Stock Antenna

Here’s the antenna, just the factory rubber duckie. As with all these antennas, they’re a compromise between size & their efficiency.

Naked Antenna!
Naked Antenna!

Giving a gentle pull to the antenna sheath while it’s attached to the radio allows it to come apart. The quality actually doesn’t look to bad. It’s very similar in construction to my Diamond X-30, just on a much smaller scale.

At the bottom of the antenna is the matching network, an inductor & ceramic disc capacitor. Here lies the problem with this antenna.

Dry Joint
Dry Joint

Here where the capacitor joins onto the feedpoint from the SMA connector, the solder joint has come away. This was a very poor joint to start with, and the solder hadn’t wetted the capacitor lead at all

After cleaning the joint, and applying some flux, a new joint was easily made with some Real Solder.

Repaired Joint
Repaired Joint

Here’s the joint freshly repaired, the antenna is now back to full working order. It even seems to work better than the others I have 🙂