Survival Radio Teardown

2018-01-15 | By All About Circuits

License: See Original Project

Courtesy of All About Circuits

Being lost in the wilderness could be the death of most people, especially when they carry smartphones that are only designed to take selfies of their demise. In this teardown, we will look at a windup radio with a few interesting features that may be useful in the wild!

The Radio’s Functionality

This radio may seem basic at first glance, but it contains many useful features. The top of the radio has a solar panel that charges the internal batteries, the back of the radio has a windup mechanism that manually charges the batteries, one side contains an LED torch, and the opposite side contains two common charging ports: USB A and USB Mini-B.

The back of the radio with the winding handle visible

The LED torch lights

The various IO ports found on the side of the radio

Interestingly, this radio contains two battery ports. The first battery port is used for non-rechargeable batteries, for regular radio use, while the second battery port is for a lithium-io rechargeable battery. While not ideal, this does mean that you can use the radio without a permanent power source, which is very handy when out camping.

The non-rechargeable battery compartment (bottom left) and the rechargeable batteries (top right)

Beyond survival, this radio can also tune to FM and AM stations. On top of that, it can also make a very loud beeping noise, which is important in situations where you may be lost or in danger. The sound can attract the attention those nearby.

The radio, volume dial, and band selector

With the outside observed and noted, it’s time to break this open and see how it’s made!

Internal Access and the Dynamo

I accessed the inside of the radio unscrewing the four screws around the perimeter of the case. However, getting these unscrewed proved to be a challenge on two fronts:

1. The hole diameter was very small, so only small screwdrivers could be used.
2. The screws were incredibly tight.

Unscrewing the screws entailed a small screwdriver and a pair of pliers that acted as a lever. Eventually, I was able to remove all four screws, revealing the innards of the radio. The good news is, this unit was put together with the intention of it not falling apart!

The innards of the radio!

The dynamo mechanism is held down with two screws, and it uses a simple gearbox to increase the revs per second. This is very important because the voltage induced in a coil by a moving magnetic field is directly proportional to the rate of field lines being cut. In other words, the faster you can turn the coil, the larger the voltage produced. Such a design is found in many dynamos, which is why they can be tough to get started. Interestingly, the dynamo has three wires instead of the expected two, and what’s even more interesting is that the magnets are moved—instead of the coil. By doing this, the motor does not need to have brushes, which is better for reliability (something you would definitely want in a survival radio). The three wires probably indicate that this is a three-phase motor (similar to ones found in floppy disks).

The dynamo and gears

Top Side PCB and Solar Panel

The solar panel (located on the top of the radio) is wired to the main PCB and has the identification yingtu 75 29mm, which returns no results online. However, some basic testing suggests that this panel can provide around 5V open circuit and 1mA when shorted. Considering that it’s winter, the power output will probably be larger, so, comparing it to other panels on the market, this device could be expected to produce around 350mW (5V @ 0.07A or 12V @ 0.03A).

The solar panel extracted from the radio

The top side of the PCB shows a solder-masked PCB, with what looks like a foil effect on the traces. This can result from tinning the PCB before applying the solder mask. There are also many component legs visible, which suggests there are through-hole parts on the other side, but there are still many surface mount parts on the top side.

The top side of the PCB

The lights are housed on their own mini circuit board

A long ferrite core rests on the top side, which is used in an LC tank circuit for selecting a specific radio station. Chances are, this ferrite rod is used only for the AM spectrum. The inductor needed in an FM circuit is very small in comparison (due to the higher operating frequency).

The ferrite core responsible for AM station selection

There is one surface mount IC of particular interest on the top side, with the identification "si4836a10". Online resources suggest that this part is manufactured by Silicon Labs and is a complete AM/FM mechanical tuning radio IC.

The SI4836A10 radio receiver IC

The block diagram for the IC (image from Silicon Labs datasheet)

The Underside of the PCB

Extracting the PCB involves removing several screws. When I lifted the PCB, it became apparent that the device was only single sided, with jumpers on the underside. Such a technique can be used to keep costs low, since the PCB is easier to fabricate this way. But it can also increase the cost of fabrication, as these parts are usually soldered by hand.

The PCB removed from its housing

The radio tunes to a station with an interesting set of gears that drive a tuning capacitor. The volume is also adjusted with the use of a small potentiometer, which is mostly made of plastic (from what a user could touch).

The underside showing the gear mechanism

The plastic gear here is screwed into the tuning capacitor

The plastic gear removed

Volume adjust potentiometer

Conclusion

This radio sports some interesting design practices, such as the use of a single-sided PCB, as well as the use of both a surface mount and through-hole parts. Constructing such a radio would involve soldering the through-hole parts first if they are wave soldered, but since there are surface mount devices too, these are probably done by pick and place, with the through-hole parts manually soldered afterward. For a survival device, this really does have a few useful features. You may not want to be without it the next time you go on an adventure!

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