SMath Studio - A Free Mathcad Alternative

While looking for a Mathcad alternative, I stumbled upon one free alternative. It's called SMath Studio and this will come in handy as I'm refreshing my undergraduate Math. This might also be useful to students who doesn't have access to Mathcad (we've had access to it back in college), or professionals who can't afford it.

Here's the URL to it.

http://www.smathstudio.com/ 

Circuits and Electronics - MITx 6.002x

7 years after graduation, I guess it's time to refresh some of my rusted fundamental analog design knowledge. What better way to do that than enroll on MIT's experimental online course, 6.002x - Electronics and Circuits. The course will be running, free of charge, from March 5 to June 8. A certificate is also awaiting at the end of the course.

Here's the URL, by the way.

https://6002x.mitx.mit.edu/

While at it, I am also refreshing most of my Mathematics. It's also a good time to learn about Multivariable Calculus which we never had back in college.

The courses can be found at MIT Open Courseware site. I'm particularly taking the ones designated as OCW Scholar which are deemed more complete than the other Open Courseware available.

Here's the URL to OCW Scholar course.

http://ocw.mit.edu/courses/ocw-scholar/ 

CD4007-Based Voice Changer

Voice Changer (Ring Modulator) based on CD4007

This project is my entry to the 7400 Contest. It's a Voice Changer/Distorter based on a CMOS IC originally intended for digital use, the CD4007 IC. CD4007 contains two Complementary MOS pairs with the third pair connected as an inverter.

Simulation: Single Balanced Modulator

Warming up for a personal project in my virtual lab. This Single Balanced Modulator based on MOS devices will be one part of the project. 

Here are some simulation screenshots before I make the actual circuit.

LTspice Transient Analysis
Circuit under test above plotted trace

LTspice FFT Analysis

Simulation: Headphone Passive Bass Enhance

LTspice simulation

Acer Aspire 4715z Touchpad Repair

Here's another quick video on a repair job on my Acer Aspire 4715z. This time, it's a replacement for the tactile switches on the touchpad (they died during the popularity of Plants vs. Zombies :D).

Acer Aspire 4715z Keyboard Replacement

My Acer Aspire 4715z has served me for 3 years now. Unfortunately, its keyboard is already missing a lot of keys (picked by my daughter Anika when she was one). Typical laptop repair costs around PhP 2000 but I found a replacement keyboard on eBay, and, it only costs approximately PhP 650 (including shipping).

Nillkin Hard Case For My Cherry Mobile Magnum

I just received my Nillkin Protective Case for my Cherry Mobile Magnum. I purchased it from ebay (at approximately PhP 870.00) as custom-fit cases and screen protectors for the Magnum are rare, if not available locally. The case is for Huawei Ideos X6 U9000 which is the same unit as the Cherry Mobile Magnum.

Android Phone Audio Signal Generator

An Audio Generator is a very useful tool in a hobbyist's lab especially during experiments and testing of audio circuits such as amplifiers. Unfortunately, this is one of those equipment that a hobbyist may not be willing to buy (that includes me) as it may not serve him much in other circuits i.e. digital circuits. Fortunately though, there are Virtual Instruments available for computers, and now as smartphones get smarter, they are now also available on phones.

Iwatsu SS-7810 100MHz Analog Oscilloscope

One great scope for serious hobbyists on a budget

HP 54503A 500MHz Digitizing Oscilloscope

Perhaps I was lucky enough to have owned this scope :D

Just Another Day At Work: Band Filter Testing

Quick and dirty Scalar Network Analyzer
Graph is noisy as there is no video filter after the detector

While waiting for a Network Analyzer, a quick and dirty Scalar Network Analyzer is realized by using an Anritsu Signal Generator on sweep mode, Analog Oscilloscope on XY mode, and a ADL5513 Log Detector. A box on the grid denotes 10dBm, thus, rejected bands are 40dB below passed bands. Both passed bands are Globe's GSM 900 bands, rejected bands are first 25 channels of Globe, and Smart's GSM 900 bands.

These Band Filters are replacement for the Frequency Shift Filters found on Globe's Frequency Shifting Repeater. The Project is to modify these repeaters to Band Selective Repeaters.

From Frequency Shifting, it's now Band Selective