A radio designer's household will always contain old diodes and transistors from radios and televisions that have become unnecessary. In skillful hands, this is wealth that can be put to good use. For example, make a solar battery with your own hands to power a transistor radio in camping conditions. As is known, when illuminated with light, a semiconductor becomes a source of electric current - a photocell. We will use this property.
The current strength and electromotive force of such a photocell depend on the material of the semiconductor, the size of its surface and illumination. But in order to turn a diode or transistor into a photocell, you need to get to the semiconductor crystal, or, more precisely, you need to open it.
We’ll tell you how to do this a little later, but for now, take a look at the table that shows the parameters of homemade photocells. All values were obtained under illumination with a 60 W lamp at a distance of 170 mm, which approximately corresponds to the intensity of sunlight on a fine autumn day.
As can be seen from the table, the energy generated by one photocell is very small, so they are combined into batteries.To increase the current supplied to the external circuit, identical photocells are connected in series. But the best results can be achieved with a mixed connection, when the photobattery is assembled from series-connected groups, each of which is made up of identical parallel-connected elements (Fig. 3).
Pre-prepared groups of diodes are assembled on a plate made of getinax, organic glass or textolite, for example, as shown in Figure 4. The elements are connected to each other by thin tinned copper wires.
It is better not to solder the terminals suitable for the crystal, as this can damage the semiconductor crystal due to high temperature. Place the plate with the photocell in a durable case with a transparent top cover. Solder both pins to the connector - you will connect the cord from the radio to it.
A solar photo battery of 20 KD202 diodes (five groups of four parallel-connected photocells) in the sun generates a voltage of up to 2.1 V with a current of up to 0.8 mA. This is quite enough to power a radio receiver using one or two transistors.
Now let's talk about how to turn diodes and transistors into photovoltaic cells. Prepare a vice, side cutters, pliers, a sharp knife, a small hammer, a soldering iron, POS-60 tin-lead solder, rosin, tweezers, a 50-300 µA tester or microammeter and a 4.5 V battery. Diodes D7, D226, D237 and others in similar cases should be disassembled this way. First, cut off the leads along lines A and B with side cutters (Fig. 1). Gently straighten the crumpled tube B to release terminal D. Then clamp the diode in a vice by the flange.
Apply a sharp knife to the weld seam and, lightly hitting the back of the knife, remove the cover.Make sure that the knife blade does not go deep inside - otherwise you can damage the crystal. Conclusion D: Remove paint - the photocell is ready. For diodes KD202 (as well as D214, D215, D242-D247), use pliers to bite off flange A (Fig. 2) and cut off terminal B. As in the previous case, straighten the crumpled tube B, free the flexible terminal G.
