This is a quick update to my previous blog post, where I explained making a touch-free surgery timer. Unfortunately, I found that it just wasn’t working well – as I explained previously, the low voltage used by that timer (1.5 V from a single AA battery) was not enough to make multiple IR sensors respond to the proximity of a finger.
After some brain-storming for how to fix this issue with sensing, I came to the conclusion that I really needed to start from scratch with a new (higher voltage) timer. I therefore scoured the internet for a timer with the following features:
- Runs at 3-5 volts (ie. two or three 1.5 V batteries), but not from button batteries (they don’t have much capacity, so would drain too quickly)
- Stopwatch and countdown timer functions
- Controlled by limited number of pushbuttons (ideally Start/Stop and Reset for stopwatch, then “add minute” button to set up timer)
- Has big light-up numbers for easy checking of timing
Finally, I found a timer that hit all my requirements, and only cost around £20 on Amazon (turns out the kind of timer I wanted with simple controls and big light-up numbers is targeted to children and the elderly):
So, I cracked the timer open, soldered in IR proximity sensors to the Start/Stop, Reset and Minute buttons, and found they worked great – I could control the timer by moving my finger to within 10 mm or so. Turns out there was some dead space inside the case, which meant that I could drill holes in the side and mount the sensors on the inside. I also added in a cutoff toggle switch to cut the power to the IR LED’s to prevent battery drain.
All in all, I’m really pleased with the new timer: I left it in the surgery room, and it’s going down brilliantly with the other lab members who’ve tried it.