[B Arnold] is hearing voices and needs help from the Hackaday community. But before any of you armchair psychiatrists run off to WebMD, rest assured that [B Arnold] suffers not from schizophrenia but rather has an RF coupling problem.
The project (which isn’t posted yet) is an attempt to turn a C.H.I.P into an Amazon Echo, for which [B Arnold] needed an audio amplifier. Turning to the junk bin, he unearthed an LM386, that venerable power amp chip that first appeared in the mid-70s. Dead simple and able to run off a 9-volt battery, the LM386 that has found its way into thousands of commercial products and countless hacks.
Shortly after applying power to the amp, [B Arnold] started hearing things – faint, far-off voices, scratchy but discernible. A bit of repositioning of wires and hands improved the signal enough for a station ID – an FM talk radio station on 97.1 MHz. [B Arnold] doesn’t mention the call sign, but it might have been KFTK out of St. Louis, Missouri; in any case, it would be helpful to know the range from the transmitter to the inadvertent receiver. Two low-fidelity audio clips are included below for your listening pleasure – you’ll want your headphones on, and Sample 2 is better than Sample 1 – as are photos of the offending circuit.
What do you think is going on here? We’ve heard of RF coupling of AM radio stations before, but how would FM signals be making it into this circuit and out of the speaker? Is there anything [B Arnold] did wrong to get this result? Sound off in the comments and let us know your horror stories of RF coupling.
Continue reading “Fail of the Week: The Accidental FM Radio”
Sometimes it’s worth doing something in an inefficient way. For example, it might be worth it in order to learn something new, or just to use a particular part. [Deater] did just that with the Raspberry Pi AY-3-8910 Chiptune Player (with LED visualizers!)
The venerable General Instrument AY-3-8910 series sound chips were common in older hardware like home computers and game consoles as well as sound cards for the Apple II family. They were capable of generating three channels of square waves with various effects. Developers eventually squeezed every little bit of performance out with clever hacks. The Raspberry Pi has more than enough power to do all this in software, but as [Deater] puts it, it’s far more interesting to use an actual AY-3-8910 from the 80’s. Some LED bar graphs and matrices round out the whole system.
All the code for the Raspberry Pi AY-3-8910 chiptune player can be found on [deater]’s github repository for the project. A video of the player banging out some sounds is embedded after the break.
Continue reading “Raspberry Pi Chiptune Player Rocks a Sound Chip from the 80’s”
The folks at [ElectroSmash] recently released 1Wamp – a one watt, open hardware, Guitar amplifier packed with features. It consists of a JFET based pre-amplifier, a Big Muff Pi a.k.a BMP based Tone control and an LM386 power amplifier. The dual JFET pre-amp provides tube-like sound, the BMP provides a nice tonal range while the LM386 can drive various types of output’s ranging from headphones to speaker cabinets.
1Wamp had controls for Tone, Volume and Gain, a Speaker/Cabinet output, a headphone output with an integrated attenuator switch and an aux. input. The aux. input is handy as it adds any line level input signal to the guitar sound, allowing you to practice with metronome or MP3 backing tracks or drum bases. It runs off either a 9V battery or can be powered via an external power source. [ElectroSmash] have released all the native KiCad design files. If you’d like a quick look at the design, check out the Schematic PDF and the Bill of Materials. There’s also a handy assembly manual [PDF] that shows how to build it in five easy steps.
Their blog post provides extremely detailed circuit analysis of every part of the design, starting from the power supply filter to remove mains “hum” all the way through to PCB layout considerations for noise reduction. Oscilloscope screen shots provide signal analysis showing bias points and signal levels throughout the circuit. The choice of value for every component is explained, along with the consequences of changing those values. This makes it easy to customise the 1Wamp to suit individual tastes. We also noticed SPICE models for the recommended and alternative JFET transistors, in case you need to customise the design by changing component values.
There’s also a lot of audio amplifier trivia, references and links shared in their post. This includes a detailed analysis of the LM386 op-amp. Want to add some bling to your 1Wamp build? There are a lot of handy tips on how to add cool LED lighting to the amplifier if it is mounted in a standard metal enclosure. However, the PCB has some really nice graphics, so an acrylic-sandwich-type enclosures look best. Check out the video that walks through the features of the 1Wamp and shows off its performance. And while on the subject of Audio electronics, here’s one of their earlier projects – an open source Arduino guitar pedal.
Documentation to this level proves several things, most notably a love for this design and deep consideration for those who will use and modify this amplifier. It’s a great pattern to follow with your own Open Source designs.
Continue reading “1Wamp, An Open Hardware Guitar Amplifier”
Crystal radios may be the simplest kind to make, but regenerative receivers are more practical and only a little more complicated. A recent design by [Selenium] is super simple because it uses a single LM386 audio amplifier IC.
You might be surprised that you can convert an audio amplifier to a receiver using just a handful of components (a variable capacitor, a coil, a handful of capacitors, and a speaker). However, [Selenium] realized he could subvert the gain and bypass pins to cause regeneration and wound up with a very simple receiver.
If you haven’t looked at regenerative receivers before, the principle is simple (and dates back to 1912). An oscillator is an amplifier that gets (theoretically) an infinite amount of gain at one particular frequency. A regenerative receiver is just an amplifier that is almost (but not quite) at the point of oscillation. This gives it very high frequency-specific gain and a measure of selectivity. You can also nudge the receiver just into oscillation to receive CW or SSB signals.
[Selenium] built his prototype on an old receiver chassis because it had the IC and the variable capacitor already in place. However, others have built successful copies on breadboards ([Austin Heller] created several good looking breadboard versions) and on PCB material. [Selenium] also released some other unique LM386-based designs that use more parts (and, probably, have better performance). Looks like a simple way to build a practical receiver.
“You can’t put new wine in old bottles” – so the saying goes. But you would if you’re a hacker stuck with a radio built in 2005, which looked like it was put together using technology from 1975. [Marcus Jenkins] did just that, pulling out the innards from his old radio and converting it to an Arduino FM radio.
His cheap, mains powered radio was pretty bad at tuning. It had trouble locating stations, and tended to drift. One look at the insides, and it was obvious that it was not well engineered at all, so any attempts at fixing it would be pointless. Instead, he drew up a simple schematic that used an Arduino Nano, an FM radio module based on the TEA5767, and an audio amplifier based on the LM386.
A single button on the Arduino helps cycle through a range of preset frequencies stored in memory. The Arduino connects to the FM radio module over I2C. The existing antenna was connected to the TEA5767 module. The radio module outputs stereo audio, but [Marcus] was content with using just a mono channel, as it would be used in his workshop. The audio amplifier is pretty straightforward, based on a typical application found in the data sheet. He put it all together on proto-board, although soldering the FM radio module was a bit tricky. The Arduino code is quite simple, and available for download (zip file).
He retained the original tuning knob, which is no longer functional. The AM-FM selector knob was fitted with a micro-switch connected to the Arduino for selecting the preset stations. Almost everything inside was held together with what [Marcus] calls “hot-snot” glue. The whole exercise cost him a few Euros, and parts scavenged from his parts bin. A good radio could probably be had for a few Euros from a yard sale and much less effort, but that wouldn’t be as cool as this.
Go deeper and explore how FM signals are modulated and demodulated for playback.
Sometimes, the best birthday presents are the ones you give yourself. In [Dino]’s case, they’re the ones you make for yourself. In honor of his 55th, he built the Sqonkbox 55, a 13-note cigar box organ based on a 555 and amplified with an LM386.
It’s based on a 555 wired in astable mode, turning it into an oscillator that outputs a frequency. This frequency is determined by the resistors between pins 6 and 7, another between 7 and 8, and the capacitor between pin 2 and ground. [Dino] shows a breadboard version first, with a single tuning pot and momentary acting as a piano key. As he explains, this portion of the circuit is repeated 13 times with pots and momentaries that he arranges like piano keys through the lid of a cigar box.
“Sqonkbox,” you ask? A second 555 in astable mode sends the output through an LED. This LED stands face to face with an LDR, and they are shrouded in this configuration with black heat shrink tubing. The ‘sqonk’ 555 changes the frequency of the first 555, providing a clippy, rhythmic tone at the rate set by a potentiometer. [Dino]’s full video of the build is after the break. A BOM is forthcoming, but it’s easy enough to puzzle it out between the video and the lovely, Forrest Mims-esque schematic. Continue reading “Sqonkbox 55 is a Cigar Box Organ of Awesome”
The Magnetophone is the latest electro-acoustic instrument from [Aaron Sherwood]. This tower contains 14 strings, and 14 hand-wound electromagnets. By energizing each electromagnet with a square wave, the strings can be vibrated to create music.
The brains of the device consist of an Arduino Mega attached to the top of the tower. The microcontroller has 6 timers, which allows for 6 notes to play at the same time. An open source tone library was used to generate square waves at the correct frequencies. These square waves are amplified by LM386 based circuits, which provide enough power to the coil to oscillate the string. By using square waves at specific frequencies, overtones of strings can be created.
This isn’t the first time we’ve seen [Aaron] combine strings and electronics. His Glockentar used solenoids to strike strings. However, this project provides new possibilities by allowing the rate of oscillation to be controlled precisely. You can see the instrument in action after the break.
Continue reading “The Magnetophone”