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Matt's Projects

Sometimes I make things

Soft Switching – Reverse engineering the LCR45

Soft switching allows a single button to be used as both an input and a power button. An example of this is the LCR45 LCR meter from Peak Electonic Design which has two buttons – on/menu and enter/off. As you can tell from the names, both buttons operate to turn the device on/off and also trigger the menu and enter functions in the interface.

This could be achieved by using both buttons only as inputs to the processor (a PIC in this case) and never turning the chip off, simply putting it into low power mode and using the ‘on’ button to wake it from this sleep. But even the best low power mode uses more power than actually turning the device off and the battery would eventually drain. So how can we achieve a multipurpose button and still use no power when turned off? To answer this I reverse engineered the LCR45 and drew out the circuit which I will now explain.

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Project: Spectrum – PCB V1, a bit of a disaster

With all of the sub-systems developed on a breadboard I moved to the next step of designing and ordering the circuit board that I would use for the final product. For now, I will skip over the design choices and jump straight to what happened when I received the board and what the mistakes were and how I have changed my design.

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Project: Spectrum – Microphone Circuit

The system needs a way to listen to the sound around it and the natural way to do this is with an electret microphone. I will probably include a 3.5mm jack input to allow you to plug music straight in too.

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Project: Spectrum – Filter Design

Frequency Response

As I said in the previous post, I want my filters to perform in the same way as the MSGEQ7. The frequency response of this chip is given in it’s datasheet.

MSGEQ7_Frequency_response.png
The 7 frequency band responses of the MSGEQ7

From the datasheet I can see that, to replicate this response, I will need 7 bandpass filters at 63Hz, 160Hz, 400Hz, 1kHz, 2.5kHz, 6.25kHz and 16kHz. Each filter will need a quality factor of 6 (this basically sets the bandwidth of the filter).

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Project: Spectrum – Beginning

It’s getting harder and harder to find spare time to work on projects. Firstly, the holidays at MIT are tiny compared to the holidays I get at Cambridge, and now that it’s finally Summer I am doing an internship which keeps me pretty busy 5 days a week, and I still want time to explore California and surrounding areas.

Anyway, I want to do a project that looks good and has some analogue electronics in it. I will build a system that listens to sound via a microphone, breaks the sound down into frequency bands and displays how loud each frequency band is using a strip of LEDs. It’s a similar idea to a Colour Organ but I want 7 frequency bands and 10 volume levels per frequency band (a total of 70 LEDs).

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Mini Project: 555 Timer Servo Control

While I wait for parts to arrive for another project, I have decided to fill the time by building a few common circuits that I have never really investigated, even though I know the theory.

One thing that I have never really investigated is the 555 timer chip, despite being a very common “jelly-bean” part. The circuit I built allows a you to control the position of a servo motor by turning a potentiometer – ie, a 50% turn of the potentiometer would result in (approximately) a 50% turn on the servo.

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Hackathon: PAL – Proximity Alert Locator

Yesterday, I had just got back from campus and was just enjoying a coffee before I got down to work when I got a message from a friend:

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“…come and build stuff…”

There was an event on campus called “Make Cool ShMIT – again!”, where they provide a bunch of components and (more importantly) pizza, and you build something in teams for 2 hours. I decided that work could wait and hopped on the bus to campus.

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Mini project: Headphone Music Controls

It’s been a long time since I posted my last update. MIT is keeping me busy – with quizzes every week for the last 5 weeks, as well as the usual helping of classes, problem sets, group projects, labs and reading.

For spring break I flew back to London to visit friends and family, so most of my free time was dedicated to catching up with people back home. But I did find some time to work on a mini project.

The idea was to build a small device that would plug into a phone’s 3.5mm headphone jack and allow me to control music by pressing buttons on the device (play/pause, volume up/down, next/previous track). I actually came up with this idea with a friend at a hackathon in early 2015, but didn’t act on it until now.

This idea isn’t really new either – it’s pretty common for this to be integrated into off-the-shelf headphones. But my headphones don’t have this, and I like my headphones.

With a little research I was able to uncover the Android specification for devices like these.

headset-circuit2
A colourful example of an implementation for Android. Source.

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Project: Remoteli – Finished

It’s been a long project. I think this is due to a combination of factors – a large number of manufactured parts, fiddly soldering and software troubles. Certainly at times I have struggled to find time to work on it, worsened by spending the year studying in America rather than the UK. Getting back into the project after waiting two weeks for a board to arrive was a challenge I faced more than once.

Nonetheless, Remoteli is now complete! (At just 39x18x4mm ignoring nuts and bolts)

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