Beaker Stand With Built-In Illumination

I am an electrochemist and it can be difficult to see what is happening in our cell solution when operating in a faraday cage or dry box. Using normal lighting devices can produce electrical noise when making low-current or high-impedance measurements. Also, normal lighting fixtures are often bulky and difficult to mount in small spaces. Flashlights are often the go-to choice, but flashlights always seem to disappear when needed the most, especially when your lab-mate steals all your stuff. So the first goal was to make a lamp to illuminate my sample solution.

Secondly, I wanted a stand that securely holds beak or sample vial. Small beakers and vials are easy to knock over unless a clamp is used. This requires a lab stand and clamps to be installed, again taking up valuable space and are generally clunky and inconvenient.

Thirdly, I wanted the stand to be resistant to spills and other solution drips.

In this project, I show you how to make a small combination beaker/vial/cell stand that includes bright battery-powered light to illuminate the test solution directly. The DC light does not add any electrical noise to sensitive measurements. The stand is also designed to securely hold your cell so that it is difficult to overturn your cell vial or beaker and thus, avoiding the need for a ring-stand clamp.

This light is not well suited for continuous use since the battery will last only about 12 hours. However, for the envisioned usage of a few minutes a day, many months of operation can be expected before the inexpensive coin-cell battery needs replacement

Features:

• 3-D printed body
• small - 60 mm diameter.
• Spill resistant.
• Physically small and low-profile
• Holds small beakers securely – preventing knocking them over.
• Easy to assemble.

Tools Needed

• 3-D printer
• Soldering station
• Flush cutters
• Carbide or diamond tip scriber/glass cutter
• screwdriver

Parts to buy or scrounge

• glass microscope slide
• solid wire (28 to 22 AWG)
• LED -- Broadcom ASMT-UWB1-NX3E2 or equivalent
• Coin cell battery holder.
• O-Ring - 2.4×17.6 mm (thickness × i.d.) or US #115 size
• 4-40, 3/4 in. bolts with washer and nut (or M3-20 mm)
• latching SPST on/off push button switch
• LED circuit board https://oshpark.com/shared_projects/YBkfP1rf or use these Gerber Files to send to a PCB manufacturer Gerber_Files for LED board.zip
• Vacuum grease.

A PLCC2 size white LED provides the illumination. It has a 4500 K color temperature for accurate colors and a wide 120 degree viewing angle to provide more uniform illumination of the beaker contents. It is also very efficient (bright) so that the battery will last a long time. These are available from distributors like Mouser or Digikey. Feel free to substitute.

The coin cell holder is a standard size and is available from many places. A typical holder has a 20 mm pin separation. An example that will work is here https://www.digikey.com/en/products/detail/keystone-electronics/1066/303562 .

The switch used for the board is an inexpensive “latching” or self locking SPST on/off push button switch. These are available from Amazon, ebay, and AliExpress and are often advertised for use in flashlights, since they change from on to off with a audible click. The ones I used are round, with two flat sides. The diameter is 14 mm, with 12 mm across the flat sides. The total switch height is about 9.5 mm. As long as the switch fits in the cavity, it should work.

You will need to print the bottom section, one of the top sections to fit your beaker, and the extra parts. These files are available as STL files and as Fusion 360 F3D files if you wish to modify the stand. For example, if you are using a 20 mL beaker, print out “bottom.stl”, “beaker_light_parts.stl”, and “top_33 mm (20 mL beaker)_4-40.stl”. The name indicates the diameter of the beaker – 33 mm, slightly oversized to fit. Files are supplied to fit common beakers of 10-, 20-, 25-, and 30-mL size plus a 7-dram glass vial.

I print the top piece with the prongs upward. Support is needed to accommodate the outside rim and O-ring grove. The bottom piece works best to be printed upside down, again supports are needed for the inner cavity.

The parts file includes the screw hole caps, the plunger for the switch, and the “sled” to hold a piece of glass for the window. These small pieces also need supports and also a raft layer to improve part adhesion. 

I used PLA filament, which should withstand any aqueous spills barring strong acid or alkali solutions. Other solvents can attack PLA but, as long as the spill is quickly cleaned and rinsed, the stand should be fine.

Once the parts are printed, remove the support material and check that the top and bottom fit together. Also, the prongs are a weak point and they can fail with a poor print, flex them gently to verify that they are strongly attached. If a prong breaks, you can probably still use the stand but printing another top piece would be best.

The light uses a very simple circuit. It is simply an LED in series a switch and a lithium coin-cell battery. Because the internal resistance of the coin-cell is quite high, no current limiting resistor is needed.

I made a circuit board for convenience. There is a ready-to-order board available on the shared repository at OSHPARK https://oshpark.com/shared_projects/YBkfP1rf . Alternately, you can use the attached Gerber files (Gerber_Files for LED board.zip) to send to the circuit board manufacturer of your choice.

A third option is to use prototyping board to make it by hand using point to point soldering. Just cut out a 30 x 30 mm piece of perf board and solder the led to the top, running wires on the bottom.

A PLCC2 size white LED provides the illumination. I used the Broadcom ASMT-UWB1-NX3E2 part, which has a 4500 K color temperature for accurate colors and a wide 120 degree viewing angle to provide more uniform illumination of the beaker contents. It is also very efficient (bright) so that the battery will last a long time. These are available from distributors like Mouser or Digikey. Feel free to substitute.

The LED is a surface mount device but is large enough that even inexperienced assemblers should be able to manage. A tip is to apply a small bead of solder to one side of the solder pad on the board and then, while holding the LED chip down with a small stick or tweezers, tack that side. Solder the other side and then return to make a better connection on the original side.

Note the orientation of the LED, the notch indicates the cathode and is the negative.

The coin cell holder is a standard size and is available from many places. A typical holder has a 20 mm pin separation. An example that will work is here https://www.digikey.com/en/products/detail/keystone-electronics/1066/303562 . The PCB board has several holes that can accommodate other variant coin-cell holders. Make sure you solder the battery holder with the correct polarity.

The switch used for the board is an inexpensive “latching” or self locking SPST on/off push button switch. These are available from many stores and are often advertised for use in flashlights, since they change from on to off with a audible click. The ones I used are round, with two flat sides. The diameter is 14 mm, with 12 mm across the flat sides. The total switch height is about 9.5 mm. If the switch fits in the cavity, it should work. These are currently available from Amazon at this link. Be careful not to buy the momentary contact type of this switch.

Connecting the switch is the trickiest part but still pretty easy, The switch is attached to the board using a solid bare wire (26-22 AWG). Solder about 20 mm of the wire to the SW_IN and SW_OUT pins of the board. Using a needle nose pliers, bend the soldering tabs on the switch up to allow the switch to fit in the cavity of the bottom 3-D printed part. Solder the wires to both sides of the switch, making sure to have a little slack between the board and side of the switch. The switch will sit slightly lower than the board when finished. Snip off any extra wire and test fit your board in the bottom cavity.

Place a coin cell in the holder and verify that the LED lights when the switch is pressed.

Place the PCB and switch in the bottom cavity of the 3-d printed part. Place the sled on top of the board. Note there is a cutout on the bottom to accommodate the switch connection wires.

The glass window is made from a glass microscope slide. Standard slides are 25 mm × 75 mm × 1 mm. Use a carbide scribe, a diamond scribe, or a small file to scratch across the glass to form a section about 30 mm long. The slide should then cleanly snap along that line. Wear safety glasses! Place the glass on the top of the sled with the O-ring on top.

Insert the plunger piece into the top plate. Making sure is moves freely. If it sticks, try rotating the piece or lightly sand the shaft of the plunger. Place the top piece on the bottom so that the O-ring fits in the groove. Optionally, use a small amount of vacuum grease in the groove to adhere the O-ring to the top piece. You can also add a small amount of grease on the inner side of the top piece rim to further increase water (solvent) resistance.

Orient the top piece so the plunger bottom is over the switch button and the bolt holes are aligned. Insert the 4-40 (or m-3) bolts and washer in the bottom plate and a nut on the top. Carefully tighten the screws to have uniform pressure on the O-ring and glass window.  

Verify that the light works by pressing the top of the switch plunger. If all is well, place the three caps into the top to hide the bolts. They should just snap in without any need for adhesive.

Admire your completed beaker light!