Relaxing/emergency Lamp With One AA Battery - Joules Thief

With a simple empty soda bottle, and a small simple circuit that we will show below you can make a device that allows you to illuminate a small room only by filling the bottle with water and adding a few drops of milk. A single AA battery is enough to power it (this device is capable of draining an AA battery down to 0.6 V, when an electrical device usually considers the battery depleted when it reaches 1.0 V).

To see the process step by step, with an explanation of the circuit in detail, as well as the preparation of the winding of the coil, do not hesitate to visit my Youtube video (subtitled in English): https://youtu.be/RnBEFtsMc-o

1) The components needed are:

-Generic NPN transistor: I used BC337, but a 2N3904 or 2N2222 may work.

-1 kOhm resistor

-Coil as indicated in the pictures: 10 turns per side is more than enough, it works with up to 5 turns per side.

-THT switch: any switch will do, a SPST is all that is needed.

-LED: I used 10 mm, but any will do.

-AA battery holder: if it has pins to solder to pcb, as I used, it is better, otherwise you will have to screw it to the PCB.

-AWG 30 wire: the thinnest wire you have can work, just a few tens of mA go through the circuit.

-Ground Wire: a bare wire will do.

-Pre-drilled plate for circuits

-Screws M2 (x2) with anti-loosening bolts

-Soda bottle cap along with part of the bottle to hold it in place

2) Tools used

* Hand drill with M1.5 and M2 drills

* Precision screwdriver: for the M2 screws

*Soldering iron together with tin

*Hot glue gun

*Pliers

*Wire stripper

Drill the 2 holes for the fastening screws to the bottle cap. When doing so, keep in mind that they must be centered in the cap at the end, but leave room in the center for the LED. Marking the cap and checking that it is centered by looking at it against the light is a good idea. You can take as reference the coordinates of the holes that I have done, see the photos (J7 & O7). Drill the cap through the holes made in the PCB.

Considering the circuit (see picture), solder the resistor and the transistor to the PCB:

Note: it is a good idea to pay attention to the soldering coordinates in the attached pictures.

a) Resistor: one pin of the resistor goes to the base of the transistor and the other solder it alone to the pcb, as it will connect to one of the coil windings.

b) Transistor: the COLLECTOR is soldered to the PCB, putting in the same hole one end of AWG 30 wire and joining them with the solder to the PCB (that wire will go later to the anode of the LED), the BASE together with a pin of the resistor and the EMITTER will go to ground, for the latter, I have bent the pin to introduce it again through the top of the PCB and solder it there to the ground wire that will distribute the ground for the circuit.

c) Solder the ground wire. When cutting it, measure the distance for it to go from the EMITTER to the opposite side of the PCB, through the PCB (to the bottom) and reach the switch there. Later on, the negative side of the battery holder will go to the same place, as it will be the other side of the switch (the switch cuts the contact between the negative side of the AA battery and the rest of the circuit ground).

It is not necessary to use wire for this circuit, except for the anode of the LED already commented: with the pins of the components properly bent is enough.

Solder the battery holder at the points indicated in the pictures, cut the excess of the positive pole pin and bend the negative pole pin so that it reaches the position where the switch will be.

The coil is very delicate, so from now on special care must be taken with this part of the circuit.

The steps to follow are:

1) Put the coil in its final position, pass the 3 ends trough the PCB (see photos) and cut the excess coil wires. Remember, looking at the circuit diagram, that the part of the winding with the two wires will be connected to the positive pole of the battery (it will be connected at the bottom of the PCB) and that the other two loose wires will go, indistinctly, one to the resistor pin that is not connected to the BASE of the transistor and the other to the COLLECTOR of the transistor, to the point where we have already made the solder that joins the COLLECTOR of the transistor with the AWG 30 wire.

2) Separate the coil from the PCB.

3) Tin the ends of the coil winding wires to be soldered. When tinning these wires, the plastic layer that covers them will be removed, so we do not need to bother to scrape it, or anything like that.

4) Once tinned, reposition the coil, glue it to the PCB with hot glue and wait a couple of minutes for it to cool down (squeeze firmly). Insert the three ends into the PCB and solder each one in its place.

Hook the PCB into the bottle cap with the M2 screws. Two tips for doing this:

1) Nuts on the inside side of the bottle cap.

2) Use the same hand to hold the PCB and the screwdriver hooked to the screw (to prevent the screw from turning) and with the other hand slowly turn the nut with the help of pliers. In the video to which I have put the link in the project description you can see how I do it.

This fastening with two screws is basic for the integrity of the circuit when opening and closing the bottle that will be the lamp. It is certainly a bit of a hassle since you have to go little by little with the nuts, but in the end you will see that it is absolutely essential.

Once the bottle cap is already fixed, drill the holes for the LED pins in the cap (through the PCB), as centered as possible, in my case at coordinates L7 and N8. Use the 1.5 drill, because it is only necessary to open the holes in the cap, the LED pins fit through the standard holes of the board.

We have delayed this step as much as possible to have the minimum possible impediments to work with the cap. As we only have the soldering of the LED left, we have to solder the switch now. Remember that one end of the switch goes to the negative pole of the AA battery and the other to the wire that distributes the ground in the circuit.

Finally, we can now solder the LED.

Method:

1) Insert the pins in their places (anode [+] in L7 and cathode [-] in N8).

2) Screw the piece of bottle you have to make a support, this forces the position of the led if it is not correctly positioned and offers limits for the bending of the pins.

3) Bend the pins to the required position (the ground one towards the ground wire and the other one to the side pointing at the transistor, to keep the LED stable).

4) Solder the cathode to the ground wire.

5) Solder the loose end of the AWG 30 wire to the anode.

And now relax enjoying a beautiful light while utilizing empty bottles and squeezing the batteries that the rest of the appliances you use at home consider depleted.