Published: April 1st, 2018 Last Modified: April 2nd, 2018
Getting tired of measuring out your buffers with a graduated cylinder like an animal? Boy, do I have a project for you! Here’s a low cost buffer dispenser that you can whip up in a few days and will run you less than 100$.
When you’re doing repetitive tasks like dispensing buffers over and over, having gadgets like the bottletop Dispensette can make a huge difference in efficiency. Just pull the plunger, depress it, and hey! presto! Out comes a measured amount of liquid. Only problem is, they run around 500$ new, not quite affordable for mundane things like electrophoresis buffers. An electronic one? try 1500$.
Now, my first idea was to try and buy an off the shelf product and modify it. Soap dispensers you put in your bathroom were an attractive option, so initially I gave that a try. Unfortunately, soap dispensers pump their liquids quite slowly and aren’t easy to modify such that they dispense volumes other than 1 mL or so.
Basically, that only left the option of building my own liquid pump that I could program myself. First off, let’s see the pump I used.
I bought one of these guys, you can find one on ebay by searching “peristaltic pump stepper motor”, they’re around 55$ CAD with the moter, and about 35$ without. The key thing here is that it can move up to 400 mL per minute, or 6 and a bit mL per second. You don’t want to wait all day for your buffer to come out.
Next comes the question, how to control this beast without rolling our own control board etc etc? Well, my go-to is usually an Arduino Uno clone board, which can be had for 4$ straight from China. As for driving the stepper motor, I had an EasyDriver lying around, which can be had for about 2$. This was very easy to hook up to an arduino, with examples straight from the original creator. Essentially, I followed “Example 2” with the exception that I modified the code to read the analog value from a 100K potentiometer (knob twirly thing) and use that to tell the motor how many steps it needs to turn.
I slapped the EasyDriver on top of some prototyping board to make a pseudo-shield for the Arduino. Both the Arduino and EasyDriver are powered by 12V from an old power supply, which plugs right into the Arduino DC Jack. The EasyDriver voltage in pin is connected to the Arduino Vin pin, which simplifies wiring a bit.
Here’s the code that the Arduino runs, use 7zip to unzip: dispenser
One improvement I will likely make is to swap out the EasyDriver for a more powerful StepStick board, the EasyDriver gets pretty hot even with the heatsink. As well, I think having multiple buttons with several preset volumes would be easier to use than a adjustable know.