LIGHT ACTIVATED RADIO

This project involves the reuse of an old battery operated radio turning it into a light activated radio. In the last step it is also suggested to use these instructions to activate through light other appliances.

-n°1 old radio working with DC voltage (battery operated);

-n°1 power supply unit providing same DC voltage as the old radio (EG: 9 or 12 V);

-n°2 photoresistors LDR, 5 mm (see picture);

Note: the model depends from the light source and the position where the radio, and the photoresistor, will be placed; according to these factors, a photoresitor already available may result adequate. A photoresistor can be tested by connecting it first with crocodile clip wires to the circuit. After the test has been successful the clip wires can be replaced by soldered wires.

 -n°1 transistor with heat sink (2N3055, NPN type; see picture);

Note: other similar transistors may be used if they are adequate for the voltages and currents foreseen for the radio. You can test other available transistors by connecting their terminals to the other parts with crocodile clip wires, that can be replaced by soldered wires once the test of the transistor has been successful.

-n°1 place for radio near light source; can be artificial light or natural light (EG: a place near, or in front of, a window);

-n°1 set of electric wires salvaged from other electric circuits (length will vary according to the distance between components connected);

-n°1 set for soldering (soldering iron and soldering wire);

Find in the old radio the + and – end terminals where voltage is provided through batteries; the voltage will be provided by the power supply unit terminals + and -.

Solder the + of the power supply to the + of the radio end terminals. If soldering is difficult You may connect the wire to the terminal with a crocodile clip, if available (see the example in the picture where the crocodile clip has been connected to the + terminal of an old radio).

Solder the - of the radio end terminals to the collector end of the transistor (for the pinout of transistor 2N3055 see the picture); if You use other transistors and You are not shure about their pinout, You should check it on internet inputing the transistor code written on them and "pinout" (EG: "2N3055 pinout").

Solder the - of the power supply to the emitter end of the transistor (for the pinout of transistor 2N3055 see the picture; for the pinout of other transistors read the previous step).

Solder one end of the photoresistors (foreseen soldered in parallel like in the picture) to the + of the power supply; the wire length should be adequate to put the photoresistor at the right distance from the light source, not too far from (it would not activate the radio), nor too near the light source (it would allow too much current to pass). Photoresistors can be tested by connecting them first with crocodile clip wires to the circuit; after the test has been successful the clip wires can be replaced by soldered wires.

Solder the other end of photoresistors to the base end of NPN transistor (for the pinout of transistor 2N3055 see the picture; for the pinout of other transistors read the previous step 2); also the wire length between photoresistors and transistor has to be adequate to the eliged position of photoresistor mentioned in previous step.

The photoresistors can be attached to the antenna of the radio, if the antenna can be extended and oriented towards the light source. They can be glued, or fixed with adhesive tape, to the tip of the antenna.

The transistor heat sink may be glued with crazy glue or with hot glue to the place where batteries were foreseen, or near it.

The soldering can be postponed after the test of the circuit by connecting the parts first with crocodile clip wires. After the test has been successful the clip wires will be replaced by soldered wires.

Test the radio; by finding the right position near the light source the radio will start, for example already tuned to Your favourite station. Once the light source is switched off the radio will stop.

If the radio is placed near a window, the radio will start/stop once the window gets opened/closed (through the movement of shutters/blinds).

By touching the photoresistors with a finger tip You can check if the photoresistors heat up when light is on or the window is open (too much current allowed because of the small resistance).

Now You can enjoy Your small domotic improvement of the house.

As anticipated at the beginning, according to Your needs this light activated solution can also be used to start/stop other devices, or open/close valves.

You only need to have a 12Vdc power source, a relay working with 12Vdc, or a valve working with 12Vdc.

The relay coil terminals, or the valve terminals, have to be connected in place of the + and – terminals of the old radio. For the relay the normally open contacts have to be soldered between the live/phase wire coming from a socket and the live/phase wire feeding the required device. The neutral and ground wires can go from the socket to the device without modifications. 

Safety note: When working with 110 or 230 Vac, please make sure that the power is not supplied to the circuit, use PPE and be sure to have a minimum of experience, in order to avoid damages to the house or to Yourselves.