Replacement for Surgical Lamp Bulbs Using LED Circuit

Step by step instructions for how to build and implement the replacement surgical lamp bulb system using an LED circuit developed by Mohammed Shafir and Zoe Englander as part of the course BME 262-Design for the Developing World at the Pratt School of Engineering, Duke University.

This system will provide a low cost and long lasting replacement for hard to acquire surgical lamp bulbs in the developing world. These instructions explain how to use the replacement bulb system with components and tools included in the kit.

Devices in the developing world that require light bulbs to perform their function are of crucial use in providing medical care. However, a major problem with the use of these devices in the developing world is that once the light bulbs break or burn out, the replacement bulbs are very expensive or difficult to acquire. Thus, many devices that are completely functional otherwise are not being used because they lack working bulbs.

One critical medical device that is afflicted by this problem are surgical lamps used in the operating room. These lights are of critical use to the surgeon in illuminating the area of interest during surgery. The absence of these lights seriously hampers the surgeons' ability to make informed decisions and also restricts the performance of surgeries to intervals in the day when there is sufficient light to illuminate the room.

We have remedied this problem with a replacement bulb system that will allow the user to replace conventional light bulbs in commonly used surgical lamps with a new illumination system composed of Light Emitting Diode (LED) bulbs. LED bulbs are much more efficient than conventional tungsten or halogen bulbs, consume less power, are more rigid (due to the absence of moving parts) and also have a much longer life span. Therefore, the LED illumination system will have much longer lifespan, be less expensive to run, and will not break as easily. The LED illumination system will only need to be installed once, and will not need to be replaced for many years.

In addition, this system is compatible with many different types of lamps, with a variety of different light bulbs. This system utilizes the original light bulb base, so the circuit can be made to be compatible with almost any size and shape of light bulb. The system will work for any lamp that uses between 7 and 24 volts DC.

Step 1: Parts List

The parts list for this design is shown in the table below. Additional parts and tools necessary for the construction of this device are:

1.) A blank PCB board
2.) Thin connection wires
3.) A hammer
4.) Soldering iron
5.) Soldering wire
6.) Krazy Glue

The National Semiconductor LM3404 1.0 Amp Constant Current Buck Regulator is used as the current regulating device. A detailed set of instructions can be found in the data sheet for this device. By following these instructions, the circuit designer can determine the ratings of the external components needed to meet their needs.

Step 2: Creating PCB

Print out the PCB layout provided here on a transparency. Get a PCB board, cut it to the right size, and place the transparency between board and the light in an otherwise dark room. Place a piece of glass over the transparency to keep the design and transparency aligned. Make sure that the transparency is oriented correctly, and the protective paper is peeled off. After about 7 minutes under the light, place the board in a bath of developer fluid. Make sure to wear gloves to protect your hands, and be careful not to splash fluids on your clothing. The developer fluid should be 1 part developer to 10 parts water.

Next, place the PCB in a pan of etching solution. Agitate the pan to make the etching process go faster. It is also helpful to heat the solution slightly. Keep the PCB in the solution until all of the copper is removed except for where the circuit design is printed on the board. The etching solution will stain your clothing, so be very careful not to splash it on yourself.

Rinse the printed board thoroughly to remove all fluids.

The printed layout is designed so that two circuits and two LED pads can fit onto one PCB board. Separate these four pieces using a saw.

Trim off any excess board to make the circuit as small as possible. Finally, drill the holes where the components will attach using a very small drill. The locations where you need to drill are shown as small circles on the PCB layout.

We used the ExpressPCB to design this board. Since this circuit uses surface mounted devices, the solder pad design needed to be done for each individual component.

Step 3: Placing Components on PCB Board

Cover the printed PCB in flux. Carefully solder all components onto board with a thin solder wire and soldering tool. The layout for how to do this correctly can be seen in the image for step 2.

Step 4: Attaching LED Bulb and Attachment Wires

Solder the LED bulb to the piece of PCB with the printed LED pad. Glue this piece of PCB to the end of the circuit so that the two pieces form a T. The aim is to have the LED perpendicular to the circuit so that the light faces downwards when the circuit is upright.

Finally, solder two attachment wires to the appropriate holes. These wires attach to the bulb connections, allowing the circuit to be powered.

The circuit is now ready for implementation.

Step 5: Removing Glass From Broken Bulb

The first step necessary in implementation of this system is to remove the glass from the broken bulb to expose the contacts that led to the broken filament.

Remove the broken bulb from its socket.

Place the broken bulb in the plastic bag (provided) and grasp the bulb from the outside at the base. Be careful not to cut yourself with the glass or hit your fingers with the hammer. Strike the top of the broken surgical lamp bulb with a small hammer. Be careful not to strike the bulb with too much force. The aim is to remove the glass and expose the contacts that originally connected the broken filament to the rest of the bulb.

Step 6: Attaching the Circuit to the Bulb

The next step is to attach the circuit with the LED to the bulb. Solder the contacts to the wires coming out of the circuit.

Heat up the soldering iron by plugging it in. Next, hold the tip of the soldering iron to the end of a piece of solder wire. This will cause the wire to melt. Carefully transfer the melted solder onto the contacts while holding the wires from the circuit in the melted solder. Briefly allow the connection to cool and ensure that the connection is strong enough. You may need to hold to components together using tweezers while you are completing this process.

**Caution: Soldering Iron is very hot, do not burn yourself!

Step 7: Testing the System

Insert the bulb base with the circuit attached in the light bulb socket, the way that you would a normal light bulb.

Turn on the lamp's power, and ensure that the LED turns on.

Testing for the light intensity of the system can by done using the Lutron LX-103 light meter.