2016-03-07 (M) Cyborg Heart Rate Sensor

A diode was added to the terminals connecting the 5V and signal. This should act as the snubbing diode. Since heat buildup was a problem this shouldn't hurt knowing that significant power was running through the transistor. The lack of a snubbing diode was not causing the heat, merely an indicator that dangerous power was going through the transistor and could easily damage the controller.

Diode soldered to sockets

An LED was soldered to a limiting resistor so it could safely be powered by 5V. No computations were made, it was simply given a 1KOhm resistor and did not light up at full power. This was already an indicator LED, not high power, but the light was sufficient for determining the microcontroller's output. A program was written to test different frequencies and duty cycles. Anther purpose of the LED was to test the heat generated by the transistor when using a low power device. There was some increase in temperature but the transistor did not become unreasonably hot, about 30 degrees Celsius, which is above room temperature.

Light attached to output terminals and a bit of my finger

Since the low current LED didn't generate much heat the problem seemed to be the coil. A larger coil was wound by wrapping paper around a piece of paper on a glue stick tube. This tube was large enough to wind a coil that would go over a finger. The paper served two purposes, the first reason was to use it to slide the coil off after wrapping (which didn't work) and the second reason was to crumple it to a tip where a power drill could clamp and spin the whole thing (which did work) to wind nearly six meters of magnet wire.

Paper winding rig

Different coils were attached to the device and allowed to run. The transistor became hot for all the coils that were worth using. Some got over 60 degrees Celcius (145 degrees Fahrenheit) which could damage the transistor.

Measuring the temperature with a non-contact infrared thermometer

The oscillating program was changed to use a much lower duty cycle which benefited the project in two ways. The transistor stopped getting hot, in fact, it stayed around 30 degrees Celsius, just like the LED. Secondly, the frequency was drastically increased since it would be attempting to vibrate a finger magnet and short bursts of frequencies were better than a single tap.

It was late at night when I was doing this and in my defense I forgot about the frequency blocking effects of inductors. Inductors allow direct current to pass relatively unimpeded but alternating current is blocked by the device. It is worth noting here that capacitors do the opposite; pass AC and block DC.

Once a program was written which could be felt easily on one coil the others were tested with the same program and ranked. On the left was a coil which didn't work at all. Next to it was a coil which could barely be felt so it was ranked one. After that the coils were ranked using the weakest coil as the standard. The next coil was approximately four times more powerful. The next two coils were easily noticeable and suitable for the project.

Coils ranked by magnetic output

The rest of the posts for this project have been arranged by date.

First time here?

Completed projects from year 1.
Completed projects from year 2

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2016-03-03 (Th)