No Touchy!

This came about when I was thinking about how to improve my surgery technique, in particular sterility. Not that I or people I’ve taught have ever had issues with infection, but maintaining good sterile technique can be difficult, and it certainly makes many routine tasks challenging. And, unlike “real” surgeons, who have a team of underlings to aid in their surgery, we researchers often undertake ours alone, or at most with a single technical helper.

So, what kind of routine tasks do we perform during surgery that could be done without touching anything? My first thought was a timer – we do a lot of virus injections with a nanoinjector, and we time how long we inject to ensure sufficient spread of the virus before retracting the needle. After much Googling and scouring of the internet, I was unable to find any “hands-free timer” that wasn’t a 30-second hand-washing timer. So I decided to develop my own.

First step to a hands-free timer is to find a switch of some kind that can be remotely activated, a proximity sensor of some kind. I wanted something cheap and crudely effective – ie. something that triggers upon proximity of an object (likely a human finger), with a detection distance of 5-10 mm. This lead me to two likely alternatives, a capacitive plate or an infrared sensor (Figure 1).

I bought some sensors to test, hooked them up to an Arduino and found that the IR sensor worked great, but the capacitive plate was very hit-or-miss. Right, so I knew which sensor I wanted to use, but now I needed to set them up on a timer. My first thought was to use my perennial favourite, the Arduino. And I did start setting that up, but then I found an old lab timer that I thought might make a quick and easy prototype (Figure 2A).

Opening the old timer up, I found that the buttons were simple conductive latches that connected the microcontroller pin to ground. All I had to do was correctly solder in the phototransistors of my IR sensors to perform the same latch, and I could activate the “buttons”. The one snag I found was that the timer ran off a single 1.5 V battery, which wasn’t really enough to produce a strong IR signal. This meant a couple of things:

  • I could only connect two IR sensors before the drain on the battery meant they ceased to function entirely; therefore, I hooked them up to START/STOP and RESET, to give me a functional stopwatch without the other functions.
  • The low power available from a single AA battery meant that even with only 2 IR sensors connected, they have low IR strength and therefore can only detect highly IR-reflective objects. It works for metal objects and gloved hands, so should work fine in surgery.

I connected up a couple of IR sensors to the existing circuit, as well as a toggle switch to turn off the power to the sensors to prevent battery drain when not in use. I then 3D-printed a box to house everything, giving me a prototype for my Touch-Free Timer (Figure 2B).

I had assumed that the timer, being so old, would not be in production any more. However, it looks like you can still buy it from lab suppliers, so I shouldn’t have any problems producing as many as are needed.

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