Lights are one of the most essential items that any backpacker would consider in his checklist. Among all the light sources which a backpacker chooses, headlamps are the best. This is because, a typical headlamp has its own advantages and practical applications. One can always argue that it can easily be replaced by a handheld flashlight or torch. But our own safety is the number one priority that matters while living outdoors. During certain situations when our survival matters the most, our hands may not be free all the time to hold a flash light. So it is always better to be hands free.
Moreover, these headlamps can be strapped anywhere. Also, one can always keep the headlamps in their hands anytime if it makes them feel better. Hence it can be used for camping, hiking, biking and various other creative applications. Overall, Headlamps are a must for anyone who wishes to have a safe night hiking experience.
In this Instructable, you'll be able to learn how I made my own 3D printed Headlamp and the circuit that I used to make the Headlamp reliable and long lasting. You might wonder what is the need for doing this project when there are so many cheap headlamps available in the market. Please beware of such cheap products. Most of those products don't contain constant current sources to drive the LEDs. They may stop functioning any time. Hence they are not that reliable. There are some products in the market that contain constant current circuits too. But they are too costly.
So to cherish the joy of making and learning how a professional headlamp circuit works, this is the right place.
The main features of my headlamp are 36hrs of battery back up under Low power mode and 10hrs of battery backup in High power mode. It can be attached to any head ie it is that flexible to use.
Step 1: Materials Required
Step 2: Need for Constant Current Source to Power the LED
>>To avoid the LED receive the current that is more than the absolute maximum current rating and prevent it from frying.
>>To obtain the desired luminous intensity by the LED.
>>To avoid high losses by the current limiting resistors which reduces the efficiency of the circuit.
>>To increase the shelf life of the LED and thereby increase the durability of the device.
Step 3: Circuitry
The circuit that I have used is very simple in design as it only consists of 2 transistors and two resistors to drive the high power LED. This circuit easily supports input voltages upto 24V and can drive any LED with a power consumption upto 5W provided the value of the resistors used are correct. For LEDs that run on cuurents less than 100mA, both the transistors can be BC547, otherwise use BD139 as is supports currents upto 1500mA. Since the circuit is extremely simple, I rigged it up on a perforated board and soldered them all.
Working of the Circuitry
If the voltage increases over 2V then a higher current will flow through the collector of BD139 and so the base current of BC547 will increase too bringing this transistor in the conduction state. But now the collector potential of BC547 becomes more and more negative, same thing happens with the base of BD139 and so BD139 will slowly “close” thus acting against the initial growth of current. In this way a stabilizing effect is achieved that provides current that is constant through the LED.
The value of the resistor connected to the emmiter terminal of the transistor BD139 can be obtained by the formula R=0.7/I
According to the datasheet of the 1W LED, if we intend to provide it a current of 300mA, the we have to choose a resistor with resistance 2.3ohms. The power consumption of this resistor is I^2*R=0.3*0.3*2.3=0.207W
The more input voltage the circuit has, the more current flows through it. When I tested my circuit, the Current flowing through the LED when I supplied it with a voltage of 3.7V was around 60~70mA. The Current flowing through the LED when I supplied it with a voltage of 12V was around 260~300mA. So, I used this observation as a feature to create two modes of operation for the Headlamp.
In mode 1 ie LOW power mode, the circuit receives direct supply from the 18650 battery. So, the input voltage in this case is 3.7V.
In mode 2 HIGH power mode, the circuit receives supply from the boost converter or the step up (XL6009) circuit. I have preset the boost converter to step up the voltage to 12V.
I have used a Single Pole Double Throw switch to toggle the circuit between the two modes. I have also used a normal two terminal switch to control the overall power to the circuit. I have connected the output terminals of the TP4056 lithium ion battery charger directly to the battery.
Step 4: 3D Printing
I have edited the custom box generated by The Ultimate Box Maker to create the necessary holes for the switches and the LED lens.
I have used the free software Fusion 360 to edit the files.
If you are using any battery other than 18650, then you can furthermore shrinkify or expand the headlamp by modifying the .step files as per the size of the battery.
Step 5: Final Assembly
When major components are connected to the circuit using connectors instead of soldering them, it is always easier to debug the circuit if something goes wrong. So I have used connectors in most places. Refer the above circuit diagram to know where all I used the connectors to attach the components to the circuitry.
The Front panel is where I have made appropriate holes to places the switches and created a gap to insert the charging port. Stick the TP4056 charging module using a double tape or a glue gun to the bottom shell in such a way that the charging socket is visible through the hole of the front panel. Accommodate all other components inside the bottom shell. Glue the LED along with the heat sink and the lens to the top shell hole as shown in the pictures. Close the box and screw it from all 4 sides.
The Loop and Hook tapes as Straps
To make the straps, I have used hook and loop tapes. Cut loop tapes in sizes of 20cm, 40cm and 4cm. also cut hook taps in sizes of 4cm, 4cm and 40cm. Now either sew them or staple them as shown in the pictures. Then attach them to the handles of the 3D printed structure.
The licence for the title pic can be found here.
It has a Attribution-ShareAlike 2.0 Generic (CC BY-SA 2.0) licence. Added this to avoid unnecessary arguments. :-P
Working video of the same can be found here.