Pulse-oximeter on a breadboard

We had another very interesting experiment as part of our BM605 course. This time we designed a simple pulse-oximeter (more accurately a pulse-volume meter) on a breadboard. It was done by students in just a single two-hour lab session. Another interesting thing about this experiment was that it worked with just ambient lighting.

We used an LDR (Light dependent resistor) as the primary sensing element for this. The LDR went into a voltage divider circuit. The resistor connected with the LDR for voltage division was carefully chosen so as to have a value equal to that of LDR resistance during finger placement in ambient lighting. The output of this voltage divider was fed to a band pass filter with cutoffs set at 0.1 Hz and 100 Hz.In the above figure, R1 is the thevenin equivalent resistance of the voltage divider.

This is the output that was achieved by two of our students Samrat and Aman. They placed another inverting amplifier stage after the filter. The signal is clear enough to locate the dichrotic notch.

Great going guys. Keep it up!

Thermoelectric cooler experiment

We had an exciting experiment last week in our BM605 lab. Students were asked to make a thermometric cooler using reverse peltier effect. We could make ice-cold water within minutes.

A peltier module, a CPU cooling fan, peristaltic pump, alluminium cooling block and a few tubes were all that was needed to do this magic. A Peltier cooler is an important component of the Thermal Cycler (also known as a Thermocycler, PCR Machine or DNA Amplifier) that is used to amplify segments of DNA via the Polymerase Chain Reaction (PCR).

Bad Ergonomics Solved with Indian Jugaad

My car boot kept opening because of this bad key design by Honda! My pocket is typically full of keys and this bugger kept getting pressed while I am sitting oblivious in my office! When this happened almost everyday, I decided to apply this Indian jugaad technology to fix it. An aluminium strip and a glue gun was all that it took. Fortunately, I could find a strip with a small hole. So the button can actually be used when required 🙂