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The Current Source

Robotics by day, electronics YouTuber by night.
Nerd 24/7.

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24) LVDTs & Coefficient of Coupling

I take a ball point pen and wind some coils around it (with the microprocessor controlled coil winder, a few vids back), use a ferrite core mounted on the ink shaft and it works like a charm. I also cover how to measure the coefficient of coupling with my crappy LCR meter.

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23) Class D Guitar Amplifier

What's more fun than combining music & electronics? Not much to say here; I made a custom class-d amplifier for guitar. It has built-in distortion similar to the circuit we did for the Bass Ackwards guitar pedal. I also make a custom speaker/enclosure. Came out ok, but I still need to do some tweaking.

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22) Using an I/O Expander IC

I've been working on a project which has been eating up all of my time and I thought I'd share part of it with you. In this video I'll show you how I connected an IO expander to a bluetooth module and use I2C to communicate with it. There's a lot of footage that didn't make the cut, mostly me banging my head on the desk trying to get I2C to work. There was some pretty delicate work soldering magnet wire to the IO expander chip, but unfortunately I don't have a good microscope solution and that footage didn't make it either. We'll have to fix that.

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21) uProc Based Coil Winder

So I need to wind some coils for an upcoming video and they need to be fairly closely matched in impedance and number of turns. In order to do that I rigged up this microcontroller based coil winder. I go through the overall theory of operation, a close look at the hardware and firmware involved. At the end you can watch the rotting fruits of our labor.

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20) DIY Stomp Box Analysis

Howdy folks. Today I pretend like I'm an analog expert! I went and built a DIY distortion pedal or stomp box as it may be more widely known. I thought it would make a good video, and a little more fun than the F5 bias downer from last month. In this video we inject a test signal into the pedal and we look at how it distorts on the oscilloscope & look at harmonics in the FFT plot. Being based on the ProCo Rat pedal from the 80's, I was curious to see what the filter response was so we do some Bode plots with the dynamic signal analyzer. Good Fun! (I accidentally swapped the in/out jacks - usually input is on the right with guitar pedals. This is where the name "Bass Ackwards" comes from.)

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19) Class-A Amplifier Build & Fake JFETs

Unfortunately I wasn't able to accomplish the goal of completing this amplifier in the time I had alotted. My plan was to build it up and take some THD measurements and show how to bias this (The F5 Class-A) amplifier designed by Nelson Pass. I ordered some sketchy JFETs from fleaBay and yup, sure enough they were fake, couldn't bias a damn thing. So I'll have to make a follow up video once I get the real JFETs in. Sorry folks, but at least it should be an interesting build!

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18) Unregulated Power Supply Design

I thought it would be interesting to do a theory video on linear power supply design. I build up a simple low voltage supply to setup the framework for the larger and more powerful split rail linear power supply used by the (Nelson Pass) PassLabs F5 amplifier that’ll show up over the next couple of videos. I begin building up the F5 supply and we compare ripple voltage between a switch mode supply and linear supplies. I also cover how to select the proper filter capacitor with some basic algebra. I went a little nuts with GarageBand an made some techno music to go along with the time lapse build. Not my cup of tea, but it was fun to make anyway! Hope you guys enjoy this LONGER video.

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17) Biasing Transistor Amplifiers

I thought it'd be fun to do some theory on my method of biasing a class A BJT transistor amplifier. I also show classes A, AB, C & D. Most of the time is spent on class A, but it gives you an idea on how to calculate a reasonable quiescent point with a predetermined load. All circuits are bread-boarded with the exception of a 2.5W class D amplifier which I demonstrate with an Adafruit PWM breakout board.

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16) Doppler Shift Experiment

This time we perform a little experiment using a switched quarter wavelength antenna array to create our own doppler shift. We then use a spectrum analyzer in zero span FM detect mode to listen to this oscillating doppler shift. I show how it was constructed with some lovely background music - loosely based on Francisco Tárrega's "Maria". I'm sure he's rolling over in his grave.

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15) Hall Effect Experiment

I decided it would be interesting to cover the hall effect. So in this video I show you a failed hall effect experiment, then we build a working test rig using gold foil - just as Mr. Edwin Hall did over at Johns Hopkins back in the day. We use a power supply to push current through the foil and measure the hall voltage with a Fluke 883A differential voltmeter. I also demonstrate an off the shelf hall effect sensor.

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14) Measure an Unknown Capacitor

In today's video we take a quick look at what a capacitor is, how it is constructed and how to measure an unknown capacitor value. I ran across a double sided copper clad blank PCB and was curious about its capacitance value. We take a look at four different methods to determine an unknown value: 1. By measuring its time constant with a function generator and oscilloscope, 2. Configured as a low pass filter and measuring its 3dB down point with a dynamic signal analyzer, 3. Calculating the value based on physical dimensions, and 4. By using a low cost LCR meter. At the end we blow apart a small length of solder with a 75uF capacitor charged up to 1.5kV!

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13) Silicon Controlled Rectifier & the Crowbar Circuit

In this video we take a look at the basics of the Silicon Controlled Rectifier, or SCR. There’s also a little history about the Shockley diode and its evolution into the four layer device with a gate terminal, better known as the SCR. Different methods of latching-on the device are covered, and methods to turn the device off. We build a little tabletop demonstration to show how to actually turn on and off. This is also the second video in which I recorded my own music - so please give a thumbs up if you enjoyed it. Thanks for watching and please subscribe!

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12) Headphone / Speaker AB Switch Aliens Style

Today is the easiest build yet that anyone can do with a handful of parts and a soldering iron. It is a Sci-Fi themed AB switch that gives you the ability to switch between your headphones and external speakers, useful for music enthusiasts, gaming rigs, recording studios and work-from-home parents who stay up until 2am working on editing videos and don't want to wake their kids up with the subwoofer. All joking aside, I love this thing. No more dropping cables behind my desk as I switch plugs on the rear of my iMac - it stays plugged in all the time!

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11) Stepper Motor Intro & Trapezoidal Velocity Profile

In today's video I give a basic introduction to stepper motors, what's inside and what makes them tick. If you've ever used a stepper motor and want to control it in a more advanced fashion than simply pulsing on and off, we take a look at a trapezoidal velocity profile to smoothly accelerate and decelerate from start to endpoint. Some discussion is also provided about why one would want to do such a thing. A stepper motor is connected to a linear actuator and we go over the basic calculations on how to determine the number of steps to travel a specific distance. This project is available on OshPark and source code can be downloaded from GitHub.

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10) Surface Mount Soldering Walkthrough

This is kind of a part 2 soldering video covering surface mount technology. The main idea is that it's actually easier than through hole soldering - really, it is! As long as you have a steady hand, a good temperature controlled soldering iron and thin enough solder, all you need is a little practice and perseverance and those pesky QA folks won't be able to discern between you and a pick and place machine. Good luck!

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9) Simple PCB Holder for Soldering on Camera

Quick video on how to make a simple PCB holder for soldering. This was made out of aluminum extrusion, but I'm sure you can use your imagination and a few tools to make something similar. Let me know if anyone ends up making one of these!

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8) Eutectic (63/37) Solder Phase Diagram Explained

The previous video #7, focused on the basics of soldering through hole components. This time I attempt to explain what's going on between eutectic and standard lead based solder using a phase diagram. Clear as mud?

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7) Soldering & Tools for Beginners

I've been soldering for about 30 years now; I've picked up some bad habits and I'd like to share them with you. I talk about some of the cheaper temperature controlled soldering stations, solder types, fluxes, flux removal and a few other related topics. But wait! Don't fall asleep yet. I also solder some thru-hole components and surface mount switches on a small motor control PCB that will make an appearance in an upcoming video. Please click subscribe and let me know what ya'll think in the comments. I hope someone out there learns something new from this. Good luck!

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6) Linux Command Line Basics

This is part 1 of many videos showing you how to move around the linux command line. In this first video we cover the commands: cd, ls, pwd, cat, mkdir, rm, rmdir and a few other quick tips. Let's face it, reading a book on how to use the linux command line will give you grey hair; Hopefully this video series will give you the jump start you need to enter the wonderful world of linux!

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5) Wireless Battery Charger Project

Check out a small demo board I put together to demonstrate Qi wireless charging, using a Texas Instruments bq51013B wireless receiver chip & Microchip MCP73837 standalone Li-Ion charger management chip. I show you the basics of designing and selecting proper tank circuit capacitance. I also included a time lapse of soldering a QFN package and all other related components. I hope someone out there finds this useful!

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4) DIY Audio Dummy Load

Here's a non-inductive dummy load for biasing tube amplifiers, with separate channels for stereo applications. I went a little overboard on the build with this one, but it'll be sitting on my bench for hopefully decades to come so I wanted something that would make Mad Max proud.

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3) Tube Amplifier Post Phase Inverter Master Volume Mod

A friend of mine had an old, sick Marshall JCM800 head which had some issues from sitting in the Florida humidity. Dirty potentiometers, squealing and he didn't like that he had to crank it up to 11 to get distortion. That's where we clean things up a bit and add a phase inverter master volume control.(Unfortunately, I forgot to add the footage of cleaning the potentiometers with DeOxit, but wow it made a difference!) The Boss HM-2 was a quick fix which I didn't even record. However, the 9V battery connector was shot - totally corroded and a broken GND wire. Simple enough to desolder and pop in a new one. Replacement 9V connector by www.skycraftsurplus.com in Orlando; What an awesome place!

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2) GPIB Screen Capture - Prologix

How to capture screen information from your test equipment using a prologix GPIB to USB controller.

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1) Measuring THD with the HP334A Distortion Analyzer

Take a little gander at measuring total harmonic distortion with the ancient, yet venerable HP334A... And a little theory on time domain vs. frequency domain analysis. A beastly HP3562 DSA also makes an appearance; I needed a workout anyway.

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