Kerry D. Wong

Avalanche transistors can be used to generate fast rise time pulses. Their usage in the hobby world was made popular following an application note (AN72) by Jim Williams and was further publicized via this EEVBlog video. Many people have built such avalanche pulse generators for oscilloscope bandwidth measurements. In this post, I will show you the one I built using a general purpose BJT as well as some rise time measurements. Continue reading ‘Avalanche Pulse Generator Build Using 2N3904’ »

I wrote a tutorial a while ago on how to hand solder fine pitched LGA/QFN chips using perfboards. While The technique illustrated works well with low pin count chips, for many people it is still a rather daunting task to solder these tiny chips that way. Also, as the pin count increases hand soldering without using a board with proper footprint becomes much harder. Continue reading ‘QFN Soldering Using SchmartBoard’ »

My seven year old 24 inch LCD monitor (Westinghouse L2410NM) started to flicker recently, so I decided to take a look inside to see what was wrong. Even before I opened it up, I had a pretty good idea of what might be the culprit. These older LCDs use CCFLs for back-lighting. CCFLs are typically quite robust. While it is not totally impossible, it is rather rare to see a failed CCFL. So most likely the issue is related to the power supply module. Continue reading ‘Westinghouse L2410NM LCD Power Supply Repair’ »

I bought an old Tektronix 2445 150 Mhz oscilloscope on eBay the other day. It was listed under “For Parts/Not Working” condition. Since the pictures in the auction listing suggested that the scope powers up and shows traces on all channels, I thought I would get it and fix it up. Continue reading ‘Tektronix 2445 Teardown’ »

The current sourcing/sinking capability of the I/O pins on Raspberry Pi is quite limited. According to the Wiki page, the current limit for each I/O block (e.g. GPIO0 through GPIO27 combined) comes at only 26 mA maximum, which is only capable of driving a couple of LEDs at a time. Also the I/O pins are 3.3V only, and going beyond the current or voltage limit could result in permanently damages to the chip. Continue reading ‘A Bidirectional Level-Shifting Buffer for Raspberry Pi’ »

Neal from SchmartBoard sent me an MSP430F5172 development board to check out. This board, according to the website, was co-designed with the University of Colorado for itw educational needs. It is actually just a breakout board for TI’s MSP430F5172 mixed signal microcontroller with added power regulator circuitry and a conveniently positioned JTAG connector. Continue reading ‘SchmartBoard MSP430F5172 Development Kit’ »

Last week, I discussed the construction of a network-capable temperature and humidity sensor using SHT21 and ENC28J60 with an ATmega328P microcontroller. In this post, I will show the results obtained so far and the techniques used to chart the data. Continue reading ‘Temperature and Humidity Logging Over Ethernet — II’ »

I did a project on temperature/humidity logging a couple of years ago. In that project I logged the temperature and humidity readings in my basement lab over the course of a year. One issue with the approach I took back then was that the data could not be observed in real time because the logged data were written to an SD card and could only be retrieved once the logging process was done. Continue reading ‘Temperature and Humidity Logging Over Ethernet — I’ »

Basic constant current dummy load using an Op Amp and a by-passing MOSFET is very easy to build and had been made quite popular following Dave’s video on EEVBlog. I happened to have an old aluminum hard disk cooler case collecting dust. The die-cast aluminum case is relatively thick, making it an excellent heat sink. So I thought why not use it to build a dummy load myself? Continue reading ‘Constant Current Dummy Load In an HDD Cooler’ »

I got myself a Raspberry Pi (Model B V2) last month. After having played with it for a while, I have to say that I really like this tiny single-board computer. Since it runs on Linux, you can compile and run your C/C++ code on it. Most popular applications have already been adapted to the ARM architecture and can be run readily on Pi. Unlike some other SBCs, Pi allows easy access to GPIO ports which makes it equally attractive for people who are interested in hardware. Continue reading ‘Adding a Barrel Jack And a Switch to Raspberry Pi’ »

A typical 3 ½ or 4 ½ multimeter can measure voltage in the low mV range and current in the low mA range. Voltage measurement in the µV range and current measurement in the nA range are typically only available in the more expensive lab bench multimeters. In this post, I will show you a simple adapter circuit that can be used for precision voltage measurement down to the µV range. Using this circuit along with the current adapter circuit I discussed earlier you will be able to perform most of the low level measurements with a 3 ½ meter. Continue reading ‘Precision Voltage Adapter For Low Voltage Measurement’ »

It is well understood that resistors are typically binned in such a way that for a given tolerance the actual resistance values are distributed within the specified tolerance but are outside the range of the next tighter tolerance specification. So for instance, when you buy a bunch of 5% 100K resistor, you can expect the values to be between 95K and 99K or between 101K and 105K. Values between 99K and 101K will be missing as they are binned as 1% resistors. Continue reading ‘100K 5% Carbon Film Resistor Value Distribution’ »

I bought a used Keithley 196 bench multimeter a few weeks ago. This is a 6 ½ digit 3,030,000 counts meter, capable of measuring voltages down to 100nV and currents as low as 100nA. It can also be used to measure low resistance with a resolution of 100 µΩ using 4-wire measurement. And because of the high input resistance on lower voltage ranges (> 1 GΩ), this meter is great for working with analog circuits where precision measurements are often required. Continue reading ‘Keithley 196 Firmware/Calibration Data Backup’ »

I have been mainly using perf-boards for my electronics projects. Since most of the stuff I build are not very complicated and are one-offs, using perf-boards has been more than adequate. With that said, I did find wiring the headers in my Arduino projects to be a big pain and depending on the number of break-out pins needed to be wired this could be quite time consuming and error-prone as well. Since I have heard many good things about Seeed Studio‘s Fusion PCB Service, I decided to give it a try. Continue reading ‘Arduino Dev PCB Using Seeed Fusion PCB Service’ »

For current measurement in the low micro-amp and nano-amp ranges, a feedback ammeter is usually an excellent choice (see Keithley Application Note 1671). Because of the very high gain of an Op-amp, the burden voltage can usually be ignored when using a feedback ammeter. Thus, the measurement results can be obtained much more accurately compared to using the shunt resistance current measurement method. Also, because of the near zero burden voltage, circuit that is sensitive to power supply voltage changes can be instrumented without affecting its operation. Continue reading ‘Current Adapter for Low Current Measurement Using TS1001’ »