Yet Another Inductance Measuring Scheme

How do you measure the value of an unknown inductor? If you have an LCR bridge or meter, you are probably going to use that. If not, there are many different techniques you can use. All of them rely on the same thing my Algebra teacher Mr. Harder used to say back in the 1970’s: you have to use what you know to get what you don’t know.

[Ronald Dekker] must think the same way. He took a 50-ohm signal generator and a scope. He puts the signal output to about 20kHz and adjusts for 1V peak-to-peak on the scope. Then he puts the unknown inductor across the signal and adjusts the frequency (and only the frequency) for an output of 1/2 volt peak-to-peak.

Continue reading “Yet Another Inductance Measuring Scheme”

Turntable Turns Waveform Generator

In need of a waveform generator for another project, [David Cook] crammed out the old turntable to modify it for a handy hack: By adding a simple reflectance sensor to the pickup he turned it into a waveform generator that optically plays back arbitrary waveforms from printed paper discs.

Continue reading “Turntable Turns Waveform Generator”

Retrotechtacular: TV Troubleshooting

As technology advances, finding the culprit in a malfunctioning device has become somewhat more difficult. As an example, troubleshooting an AM radio is pretty straightforward. There are two basic strategies. First, you can inject a signal in until you can hear it. Then you work backwards to find the stage that is bad. The other way is to trace a signal using a signal tracer or an oscilloscope. When the signal is gone, you’ve found the bad stage. Of course, you still need to figure out what’s wrong with the stage, but that’s usually one or two transistors (or tubes) and a handful of components.

A common signal injector was often a square wave generator that would generate audio frequencies and radio frequency harmonics. It was common to inject at the volume control (easy to find) to determine if the problem was in the RF or audio sections first. If you heard a buzz, you worked backwards into the RF stages. No buzz indicated an audio section problem.

A signal tracer was nothing more than an audio amplifier with a diode demodulator. Starting at the volume control was still a good idea. If you heard radio stations through the signal tracer, the RF section was fine. Television knocked radio off of its pedestal as the primary form of information and entertainment in most households, and thus the TV repair industry was created.

Continue reading “Retrotechtacular: TV Troubleshooting”

Arduino Masters Ham Radio Digital Mode

[jmilldrum] really gets a lot of use out of his Si5351A breakout board. He’s a ham [NT7S], and the Si5351A can generate multiple square waves ranging from 8 kHz to 160 MHz, so it only stands to reason that it is going to be a useful tool for any RF hacker. His most recent exploit is to use the I2C-controllable chip to implement a Fast Simple QSO (FSQ) beacon with an Arduino.

FSQ is a relatively new digital mode that uses a form of low rate FSK to send text and images in a way that is robust under difficult RF propagation. There are 32 different tones used for symbols so common characters only require a single tone. No character takes more than two tones.

Continue reading “Arduino Masters Ham Radio Digital Mode”

Hacking a $100 Signal Generator

Signal generators are a useful piece of kit to have on your electronics bench. The downside is that they tend to be rather expensive. If you have $100 to drop on a new toy, the MHS-5200A is a low cost, two channel, 25 MHz generator that can be found on eBay.

The downside is the software. It’s an ugly Windows interface that’s a pain to use. The good news is that [wd5gnr] reverse engineered the protocol so you don’t have to. This means other software can be developed to control the device.

When connected to a computer, this function generator shows up as a virtual USB serial port. The documentation that [wd5gnr] assembled lists all the serial commands you can send, and what they do. If you aren’t into manually setting waveforms from a serial terminal (who is?) there’s a tool for doing that automatically on Github. This takes in a CSV file describing a waveform, and programs the generator to make it for you.

The software is also compatible with Waveform Manager Plus, a free GUI tool for defining waveforms. Putting this all together, you can have a pretty capable waveform generator for less than $100.

Antique Case for Custom File Server

Michigan Tech was throwing out a bunch of old electronic equipment, and [Evan] snagged quite a gem: a UHF signal generator built by Hewlett Packard circa 1955. He stripped all of the remaining electronics out of the case, but kept the slide-out trays and the front instrument panel to create this antique-looking file server.

The bottom tray was where the bulk of the electronics were housed, and since widespread adaptation of transistors for electronics wasn’t common at the time (the first silicon transistor wasn’t made until 1954), the original equipment was all vacuum tubes. This meant that there was just enough space for a motherboard, heat sink, and a couple of power supplies.

The hard drives are held in custom housings in the top portion of the case. The real magic, however, is with the front display panel. [Evan] was able to use the original meters, including a display for “megacycles” which is still technically accurate. The meters are driven by a USB-to-serial cable and a python script that runs on the server.

The antique case is a great touch for this robust file server. Make sure to put it in a prominent place, like next to your antique tube radio.

An Audio Based USB Oscilloscope and Signal Generator for $20

SoundScope

Are you interested in building a 20kHz 2-channel oscilloscope and a 2-channel signal generator for only $20 with minimal effort? Be sure to check out [Jan_Henrik’s] Instructable that goes over how to build this awesome tool from a cheap USB audio card.

We have featured tons and tons of DIY oscilloscopes in the past, but this effort resulted in something very well put together while remaining very simple to understand and easy to build. You don’t even need to modify the USB audio card at all. One of the coolest parts of this build is that you can unplug your probe assembly from your USB audio card, and bring it wherever your hacking takes you. After the build, all you need is [Christian Zeitnitz’s] Soundcard Oscilloscope program and you are good to go. One of the major downsides that is often overlooked when using an audio based oscilloscope, is that it is “AC coupled”. This means you cannot measure low-frequencies (including DC signals) using a sound card. Be sure to heed [Jan_Henrik’s] advice and do not use your built in audio card as an oscilloscope. With no protection circuitry, it is a sure fire way to fry your computer.

What analog projects have you built around an audio interface? We have seen such an interface used for many different applications, including a few fun medical related hacks (be sure to keep safety your first priority). Write in and let us know!