How to Make a Constant Power Light Source for the OPN Fluorimeter and Other OPN Lab

EquipmentJohn Giannini

St Olaf College, Northfield MN 55057

Introduction

We recently shared a design for an inexpensive fluorimeter (OPN fluorimeter) that students could build and learn the principles of fluorimeter function. One major limitation to our design was that the LED flashlight we used would drain the batteries very quickly. As the batteries drained the light intensity would decrease adding to measurement error. This was significant when creating a standard curve and using it to calculate an unknown concentration. When using acridine orange as our fluorescent probe we would underestimate the unknown sample by an average of 10%. In this short paper we show how to build a constant power light source using a few inexpensive parts that greatly improves the fluorimeters accuracy ( +/-2%).

Materials

-3D printed OPN fluorimeter and associated parts

-3V regulated power supply

- 2 pole button switch (7101 C&K)

- soldering iron or alligator clips

-3D printed button switch holder

- small piece of 20 gauge wire (about 6”)

Basic Schematic of the Light Source

Construction

Step 1 . Assemble all your supplies and components. (figure1)

Figure1. The components needed to construct the light source.

Step 2. Take the end cap off of the flashlight and remove the battery. Now with a hack saw cut the body of the flashlight as illustrated in figure2.

Figure 2. The body of the flashlight after being cut with a hack saw.

Step 3. Now extend the body of the flashlight as far as it will pull out then glue it with super glue so it will no longer move in or out (figure 3).

Figure 3. Gluing the body in place so it will no longer move.

Step 4. Cut off the end of the power supply cord. (figure 4).

Figure 4. Cutting the end of the power supply cord with a pair of wire cutters.

Step 5. Pull the wires on the power supply apart and cut the wire without the white stripe(+electrode) 16 inches from the end (figure 5).

Figure 5. Pull the wires apart and cut the wire without a white stripe.

Step 6. Assemble the 2 pole button switch in the 3D printed holder (figure 6).

Figure 6. The 2 pole button switch assembled in the 3D printed holder.

Step 7. Solder the cut wire ends to the poles on the button switch (figure 7).

Figure 7. The wire ends soldered to the button switch.

Step 8. Solder the other end of the cut wire to the spring inside the cut off light body (figure 8).

Figure 8. The cut wired soldered to the spring inside the light body.

Step 9. Run the wire that was not cut through the side holes in the 3D printed button switch holder. Trim the wire so it is the length of the wire soldered to the light spring (figure 9).

Figure 9. The wires assembled in the switch holder.

Step 10. Attach the alligator clip to the end of the uncut wire. You can solder the connection or connect it with the supplied screw (figure 10).

Figure 10. The alligator clip attached to the uncut wire.

Step 11. Scratch the paint off of a small area on the inside of the flashlight body. This is so the alligator clip will make a good connection (figure 11).

Figure 11. Using a file to scratch the paint of the inside of the light body.

Step 12. Attach the alligator clip to the light body where you have removed the paint (figure 12).

Figure 12. The alligator clip attached to the light body.

Step 13. Insert the light body into the fluorimeter tube. Use a 3D printed spacer for a good tight fit (Figure 13).

Figure 13. The light inserted into the fluorimeter.

This updated light source is constant and durable and can be used in other OPN lab devices such as the epi-fluorescence microscope (figure 14).

Figure 14. The constant power light source inserted into the epi-fluorescence microscope.