A few years back, I bought a whole bunch of Fisher brand pipette tips and now my lab is cluttered with a bunch of empty plastic boxes now that the tips have been used and disposed of.  I needed a quick project enclosure to build an instrument for a student and thought this might be an interesting exercise in repurposing.

One of the projects in my lab involves making a controlled water flow system.  As I’m interested in instrument design, I want to build as opposed to buy the device.  It’s a pretty straightforward design, involving an inexpensive peristaltic pump from Adafruit, a motor driver (I use an H-bridge which is overkill for this project since I don’t bother with flow in both directions), a 555 timer for pulse width modulation to control the pump speed and a LM317 voltage regulator since the pump wants 12 V but I only want 5 volts going in to my chips.  I had some spare on/off switches, a potentiometer and DC power supply lying around which completed the package.  The innards look like this:

At first, cutting out the holes in the box was a bit cumbersome.  Using a sharp blade wasn’t getting me anywhere (other than an inevitable trip to the emergency room) and the hole needed for the pump is much too large to be drilled by a standard drill bit.  I then recalled that I have a Dremel tool collecting dust in one of my closets.  The sander/polisher attachments worked very well at carving away the plastic of the box, and so long as I didn’t set the speeds too high (and melt the plastic), I had a fairly straightforward and not-too-messy process.

I didn’t have the correct fasteners to keep everything in place, so a bit of insulated wire is all that is keeping the power plug and pump in place (the on/off button and potentiometer knob both had the correct fasteners).  Soldering everything in place was a bit of a challenge (you know, that iron is hot, and the plastic melts) but I was capable of keeping the two separate until the very (a little burn on the right hand side, which is only cosmetic – and I wouldn’t say cosmetics was a high priority in this build).

So now I have a basic, adjustable water flow system.  Preliminary results show that the range of flow rates isn’t huge (about 0.5 to 1 mL/s) and the reproducibility looks good.  The stats are for my student to work out, so I’ll know more once he reports back to me.  Overall, this was a fun, simple build to increase the functionality of a peristaltic pump with some left-over parts (box, power supply) and I hope that it can be use to learn some interesting science.