Category Archives: Circuits & Electronics

Fix: Samsung Galaxy S3 not charging, charges slowly or charge toggles on and off

s3-charging-smallPretty soon after I bought my brand new Samsung Galaxy S3, it began to be erratic charging behavior. It would often not charge, charge slowly or rapidly switch/toggle between charging and not charging. Searching on the web didn’t yield any good solutions, with most sites arguing about whether the cable, phone, or software was to blame.

The charging cable seemed suspect, since it would work better sometimes if I manually held it at a particular angle. However, even if I used a brand new cable, our car’s USB cable or my wife’s cable (which was still working for her S3), my phone had this problem. After a few months, my wife’s Galaxy S3 started having the same problem. Continue reading Fix: Samsung Galaxy S3 not charging, charges slowly or charge toggles on and off

How to fix: Pantech Jest battery will not charge

My wife’s new Pantech Jest cell phone won’t charge its battery. This has been a recurring problem with new batteries we get for it, too: inevitably it always ends up refusing to charge the battery. If you plug the phone in to charge then the phone will turn on and power up, but it will not give any indication of charging. Then no matter how long it is plugged in, the moment the phone gets unplugged it instantly turns off. The first time this happened our wireless provider replaced the phone, but the new phone exhibited the exact same behavior right out of the box. This meant that the battery was at fault, not the phone, so then our wireless provider replaced the battery which did fix the problem. However, a few weeks later the exact same thing happened. So they gave us another replacement battery (which fixed the problem again). But now this week the same problem has happened a third time. Fortunately there is a solution. Continue reading How to fix: Pantech Jest battery will not charge

DC-DC switching voltage regulator: Buck converter

Power MOSFETWhen I took a power electronics course at MIT (6.334) almost two years ago I instantly fell in love with the simplicity and ubiquity of switching power supplies. They are so simple and interesting that I decided to devote a few posts here describing how they work. Voltage regulators are interesting and useful to learn about because they are used everywhere. Electronic components (for example, those within your home electronics equipment) often require different voltages, so voltage regulators included in the equipment to generate those voltages. The first question to answer in this post is “What is a voltage regulator”: Continue reading DC-DC switching voltage regulator: Buck converter

Convert 120 V AC to 3.3 V DC without a transformer

I finally made some progress with the AC to DC converter (without using a transformer.) I recently graduated from NAU and got a job, so I actually have a little more time on my hands to work on stuff like this (even with a 3-month old baby.) If you will remember from my previous post on this topic, the challenges facing this project are that it should convert 120 V AC to 3.3 or 5 V DC, handle a relatively high output current (more than 15 mA, and the more the better), have a small profile (so no transformer or huge capacitor,) and draw very little current when no load is attached. Continue reading Convert 120 V AC to 3.3 V DC without a transformer

Final Freqency Synthesizer Design

Unfortunately, I never had the extra time needed to post the progress of the frequency synthesizer school project. However, you can view all the info pertaining to the project at the website I created for the project: (Alternatively you can try to find it posted somewhere at, but they are always changing the address of our project’s page.)

Frequency Synthesizer

The Electrical Engineering Department at Northern Arizona University (NAU, where I am a student) provides a senior level capstone design course for students. The senior students are grouped into teams and work with sponsors to complete an advanced engineering project. Our senior capstone design team is working with our sponsor, Wulfsberg Electronics, and we will be designing and implementing a frequency synthesizer for them. Wulfsberg Electronics is designing a new communication radio product that will utilize newer and smaller parts than those currently being used, and our project will be a part of their new product. Continue reading Frequency Synthesizer

Coil Gun Results and Explanations

Several months ago when describing how the build the coil gun, I mentioned that I would explain some of the “extras” that we implemented in our coil gun project. I will explain the mounting brackets and the opto-interrupters here, as well as why a coil gun works.

How it works
When a current flows through a coil of wire a directed magnet field is induced inside that coil proportional to the current. After the capacitor is fully charged we discharge the capacitor into the coil. This provides a large current in the coil thereby inducing a strong magnetic field. The projectiles that we use are made of steel which contains a lot of iron, a ferromagnetic material. The magnetic field in the coil aligns the magnetic moments in the iron which makes the iron attracted to the center of the coil. The brief discharge of the capacitor finishes before the projectile reaches the middle of the coil so the projectile continues instead of stopping in the middle of the coil. Continue reading Coil Gun Results and Explanations

Simple Coil Gun

Barrel of the coil gunThe next project that I’ve been working on (with a lab partner) for my electromagnetics course is an “EM Buffet Lab.” In other words, we get to choose what we want to build, as long as it is EM related, and then do a write-up about why and how it works. What my lab partner and I are building is a coil gun. We have actually already finished it, but we are still preparing our presentation and report for Wednesday.

Note: Be sure to also read the follow-up post to see the projectile velocity and some other goodies.

What is a coil gun?
A coil gun uses a solenoid (coils of wire wrapped closely together) to create a magnetic field. This magnetic field attracts a ferromagnetic material during a strong, brief current discharge (usually produced by a capacitor.) The projectile wants to go to and stay in the middle of the solenoid due to the induced magnetic field, but by the time the projectile gets to the middle of the coils, the capacitor is fully discharged and no magnetic field exists anymore. Therefore, the projectile does not stop, but continues traveling through the solenoid instead of stopping in the middle of it. Continue reading Simple Coil Gun