How to Drive a Latching Relay

Latching relay (a.k.a. impulse relay) can be turned on and off by momentarily applying a voltage across the relay coil. The relay would maintain in its last switched state without the need to maintain the coil current. In this post, I will show a simple circuit which can be used to drive such relays. In the video towards the end, I also included more explanations and some demonstrations.
Read more…

T is for TWT

Traveling-wave tube (TWT) is mainly used to amplify signals in the microwave frequency range. Unlike most vacuum tubes, which had largely given way to their more elegant semiconductor counterparts many decades ago, TWT is still being widely used today in many areas, especially in places where low noise and high output power is needed. I had always wanted to get my hands on one so when I saw an old HP 493A microwave amplifier for sale for peanuts, I simply could not resist snatching it.
Read more…

Visualizing Comparator and Op Amp Hysteresis

Hysteresis can be added to a comparator circuit to improve its stability, especially when the input signal is noisy. In this post, we will examine the hysteresis characteristics of some common comparator and Op Amps using an oscilloscope.
Read more…

Testing an RTL-SDR Spectrum Analyzer

Using software defined radio such as the popular RTL-SDR (1, 2) as a spectrum analyzer is nothing new (examples can be found on HackADay and EDN). In this blog post, we will discuss some of the do’s and don’ts when using SDR as a spectrum analyzer and look at some measurements I took using the popular NooElec SDR based on Realtek‘s RTL2832U DVB-T demodulator chip and Rafael Micro‘s R820T tuner chip.
Read more…

Keithley 197 Battery Option Build

I have been quite happy with my fixed-up Keithley 197 5 ½ digit bench meter purchased from eBay (you can find the teardown pictures here) earlier this year. Keithley 197 has a battery pack option (Model 1978), and this option allows it to run on battery power for 5 hours without having to plug into the mains. While it is far from being a truly portable meter, its performance easily surpasses most hand-held multimeters. So I decided to build the battery option myself and hopefully I would be able to use the meter more often in places where power outlets are not available.
Read more…

Using Arduino Due’s True Random Number Generator

Arduino Due uses an Atmel SAM3X8E ARM Cortex-M3 CPU, which has a native hardware based True Random Number Generator (TRNG). In this post, we will take a brief look at how to use it in the Arduino environment and take a look at some of its statistical characteristics.
Read more…

Building And Characterizing A DIY RF Power Sensor

Ever since I got my HP 436A power meter, I have been looking around hoping that I could obtain a compatible power sensor (e.g. 8484A) at a reasonable price to go with it. But these power sensors are quite expensive on the second-hand markets and even a non-functional unit can cost more than a hundred dollars. Since like most hobbyists, my requirements for a power sensor is not that high, I decided to build a simple RF power detector myself.
Read more…

On Arduino Due PWM Frequency

I just got myself a couple of Arduino Due boards. While they were released almost two years ago, I have not really got a chance to look at these until quite recently. Arduino Due is based on Atmel’s ATSAM3x8E 32-bit ARM Cortext-M3 processor. The processor core runs at 84 MHz, which is significantly faster than its 8-bit AVR counterpart ATmega328p which runs at 16 MHz. For an ATmega328p, the highest achievable PWM frequency is 8Mhz (square wave), so we should be able to generate much higher frequency signals on an Arduino Due. But how high can we go? Let’s find out.
Read more…

HP 8642B Teardown Pictures

In my last post, I showed my LED backlight mod of the HP 8642B synthesized signal generator. And during the process, I also showed some pictures of the A1 (keyboard and LCD) module and A2 (modulator) module alone with an intriguing Easter egg message in the firmware. In today’s post, I will do a full teardown of each module and take a closer look at what’s inside.
Read more…

HP 8642B Backlight Mod

If you take a look at the picture below, you may recognize immediately that it is a picture of an HP 8642B synthesized signal generator. But if you take a closer look, you probably will notice something different if you have ever used an HP 8642B before.
Read more…

A Four Channel Remote Control Using EnOcean Pi

In my last couple of blog posts, I did a brief overview of the EnOcean Pi sensor kit from Newark and demonstrated how to compile and run the example code using a Raspberry Pi. In this blog post, I will show a real world example – a four-channel remote control built using the EnOcean Pi in conjunction with the EnOcean pushbutton module.
Read more…

Compiling and Running EnOcean Sensor Kit Example Code

In my previous post, I took a quick look at the EnOcean sensor kit from Newark for Raspberry Pi and tested its basic functionalities using the Fhem home automation software. In this blog post, I will walk you through the process of compiling and running the example code that comes with the EnOcean Link library. While there are instructions on how to do this, some of the information is out-dated and hard to follow. So I will provide my own step-by-step instructions here.
Read more…

A Quick Overview of the EnOcean Pi and EnOcean Sensor Kit

I recently got the EnOcean Pi and EnOcean sensor kit from Newark. The sensor kit includes a temperature sensor module (STM330), a magnet contact transmitter module (STM320) and a pushbutton transmitter switch module (PTM210). The EnOcean Pi module is a receiver adapter board that connects directly to the popular Raspberry Pi. It is a gateway for handling the all the communications with the wirelessly connected sensors.
Read more…

Wavetek 907 Repair, YIG Oscillator Teardown

As I mentioned in my previous posting, there was an issue with my Wavetek 907 microwave frequency generator. While everything was fine during my initial testing, the frequency display is now stuck with an out-of-range display and the adjustable frequency range is limited to between around 6.9 Ghz to 7.9 Ghz (instead of all the way up to 11 Ghz). My initial suspicion was that the PTC heater inside the YIG-Gunn oscillator was malfunctioning. But as it turned out, it was something else.
Read more…

Wavetek 907 Signal Generator Teardown

Since I just got myself an HP 5350B microwave counter and I had fixed it up, I thought it would be great if I could get a SHF generator to test out the counter in the microwave range. So when I saw a super cheap Wavetek 907 for sale on eBay, I simply could not pass it up.
Read more…