Metal Detector

Link to my Bill of Materials: here

Link to my Build Plan: here

Name

Ethan M

Area of Interest

Electrical Engineering

School

The Bay School of San Francisco

Grade

Senior

Final Milestone

With my final milestone, I tried to clean up the design and “finalize” the project. I did this with paint, a better handle and more quality assembly. I also described some upgrades I was planning on doing if I had more time. One of these is a dial that would control the pitch of the tone coming out of the speakers. This would add a nice level of polish as well as making it easier to listen to. I would also like to add a button where the trigger of the water gun would be. I believe this would make it feel more natural to use.

Second Milestone

I have made lots of progress since my first milestone video. I haven’t made any changes to the actual circuit but instead, I built the chassis for the device. I first permanently mounted the breadboard in the electronics box. I lengthened the wires so it would reach all the way down the pipe, I installed the coil onto the bottom of the pipe, made a handle out of a water gun with the barrel cut off, and mounted it onto the pipe as well. For the future milestones, I plan to build a more effective button and add a potentiometer so the tone can be changed.

First Milestone

For the first milestone video, I showed my progress with the metal detector up to this point. So far, I have gone through one circuit and determined that it never would work, as it was missing components in the schematic. From that setback, I moved onto a new circuit from a much more trusted website (here) I first built it on a traditional breadboard. That worked great. It started right away and detected made the appropriate noises when metal was present. The main issue was the general impermanence of the plug in breadboard. This was such an issue that when I was putting it away the day I built it, I accidentally ripped out a capacitor, and this fried the main processor. The next day, I rebuilt the breadboard and started transferring the parts to a solderable breadboard. This was unusually difficult. I just couldn’t seem to get it right. Something was always in the wrong place. After about seven revisions, it finally worked. My future plans are to make the speaker louder, build the chassis for the device and wind a larger coil. The chip that the metal detector is based on is a NE555P. It is the most commonly produced chip in the world. It is very versatile and cheap. It is essentially a oscillating timing chip. For my purposes, I am using the oscillating function. When there is a magnetic substance near the coil, the resistance changes. That change in resistance then goes through the capacitor, which irons out the signal so it doesn’t spike and kill the chip. It then goes into the chip and affects the oscillation. If the object being measured acts like a coil, it raises the frequency, and if the item is dense, it lowers the frequency. The image below shows the circuit.

TV-B-Gone Starter Project

For my starter project, I selected the TV-B-Gone. This device is used to turn off any TV that has an IR receiver. I soldered all the components to their required spots and assembled the parts together. In the end, it was not the building that was the most difficult but the explaining. I had to do lots of research in order for me to fully understand how all the parts worked together. Now I am able to explain what happens from when you press the button to the LEDs firing. When you first press the button, it resets the IC. When the IC resets, it uses its internal 8mhz timer to send a signal out to the first transistor. That transistor than uses its own much more robust timer to regulate and send voltage to the four IR LEDs. These LEDs then light up at the frequencies that are most common for different TVs. The blue LEDs are for more concentrated beams and the white LEDs are for wider beams.