Inexpensive Colorimeter

thingiverse

This is a colorimeter that relies on LEDs for both light source and measurement. Assembly Instructions Below is a detailed description of assembling a colorimeter suitable for use in an introductory chemistry course. Using plastic pieces made with a 3D printer along with some minimal wiring supplies, it's possible to construct this device for around five dollars. This guide assumes only a very limited knowledge of 3D printing as well as very basic wiring skills. No soldering is necessary and the only tool needed is a screwdriver. Materials: • Plastic housing – three pieces • AA battery case with on/off switch • Two AA batteries • Four hundred ohm resistor • Five screws (#4 x 3/8 inch pan Phillips for metal) • Banana socket • Electrical tape • Three small wire nuts • Five millimeter LED • Ten millimeter red LED • Voltmeter The files required for printing the plastic portions are Mendez – Colorimeter-Top.stl, Mendez –Colorimeter - Center.stl, and Mendez – Colorimeter - Bottom.stl. The colorimeter described here was printed on a Makerbot Mini with standard settings (two shells, twenty percent infill and 0.2mm layer height). Circuit The operation of this device is based on two circuits. In the first, two batteries power a source LED. The light from this LED induces a voltage change in the detector LED that's measured by a voltmeter. Assembly Step 1 - Begin assembly by placing the battery case into the bottom casing, ensuring the switch on the bottom lines up with the opening on the casing. The wiring sticks up near the corner without any screw holes. Step 2 - Thread the wiring from the battery case through the large hole in the middle casing piece. The middle casing piece sits on the inner ledge of the bottom casing with the three screw holes lining up. Carefully screw in the three screws, using some force may be required to start them. Be careful not to create new holes while screwing, which could disrupt the alignment of the other screws. Step 3 – Insert the source LED into the smaller hole in the middle casing. Applying some pressure with your thumb may be necessary but it should snap into place. Spread the wires apart and use electrical tape to ensure they stay apart. Make sure both wires are unobstructed and still accessible for later steps. Step 4 - Using wire connectors, connect the red wire to the negative terminal of the LED (the short one). Next, connect the resistor to the black wire and then to the positive terminal of the LED. Don't turn on the battery without a resistor connected; this could burn out the LED. Step 5 - Now is a good time to test the system. Turn on the battery case and look for a light. Remember, LEDs are not multi-directional; if the wiring is switched, it won't work. Assemble the detector apparatus by attaching the ten millimeter LED to the banana socket. The short lead of the LED should be connected to the red, while the long lead should connect to the black. Step 6 - Insert the ten millimeter LED into the larger opening on the middle casing piece. Like the source LED, it should snap into place but may require applying pressure. Use electrical tape to ensure it stays in place while you place the cover on in the next step. Step 7 - Carefully place the top casing piece on top, lining up the openings for the cuvette and banana socket. There is plenty of room for the wiring, but you may need to move the source LED wiring so that it doesn't stick out the sides. Secure the top to the middle with two screws, being careful to line up the holes. Step 8 - Once the case is on, connect it to a multimeter and test the device. If everything is working, you should read a voltage around one volt with a blank cuvette in the holder. Additional Considerations: • While any five millimeter LED in the visible spectrum should work, the resistor and battery described above are tuned for conventional five millimeter red and green LEDs. Other LEDs may turn on but may not be bright enough to register on the detector. • The intensity of the light and the range of source LEDs can be modified by adding or removing resistors or changing the voltage of the batteries. • A ten millimeter cuvette can hold around three milliliters of liquid, but because the LEDs are so low in the device, only one milliliter is actually required. • While the top of the cuvette remains open, this was found to have no noticeable effect on the resulting absorbance data. • If the voltage reading on the multimeter is negative, then you probably switched the wiring on the detector. This is fine for the detector, but the source LED won't turn on if wired incorrectly.