Simple 555 Based Drone Synth

Today I have another very simple breadboard project based around the 555 timer. I’ve built three 555 astable oscillators similar to what I used in my 555 Serial Oscillator Project. This time however instead of connecting the oscillators in series I have run their square wave outputs through a simple mixer onto a single audio channel. This is known as a drone synthesizer

As you can see from the schematic this drone synth is a fairly straightforward build. If you are familiar with 555 oscillators you probably recognize the layout of the 555 chips as a basic astable oscillator almost directly out of the 555’s datasheet. Once the three oscillators were created I added a 1K ohm resistor to the output of each (pin 3) and connected these outputs together. Once the three outputs are connected you can run this through a large capacitor (I used 330 uf) and out through your output jack. It is also possible to connect this circuit directly to a speaker though the audio level may be a bit low without amplification.

Once you’ve built this circuit you can begin experimenting with it. Pin 5 on the 555 chip can be used as a control voltage input so you could easily add a method of control voltage to this circuit. The easiest way to do this would be to build three more 555 oscillators and connect their outputs to pin 5 of the 555 chips in your drone synth. These will function as basic LFOs and modulate the frequency of the drone’s oscillators. You could also experiment with other voltage controls like a sequencer or keyboard. You could also replace one or more of the potentiometers with things like photo-resistors or body contacts to make the project even more interesting.

Lastly I wanted to mention that this drone synth is not limited to three oscillators. You can add as many 555 oscillators as you want in parallel to make an even deeper and stranger sound. If you’re interested in seeing the extreme of this a YouTube user by the name of Look Mum No Computer recently built a 100 Oscillator Drone that is definitely worth checking out.

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Atari Punk Console – Adding LFOs

Today I wanted to show you guys something new I’ve been playing with on the breadboard. Essentially what I have here is a twist on a classic project. I’ve taken an Atari Punk Console (Stepped Tone Generator) and added two 555 timer based oscillators as LFOs to add more depth and interest to the sounds produced.

This modification is built on one simple characteristic of the 555 timer (and by extension the 556 which consists of two 555 timers). This is the control voltage pin which allows you to use an external voltage source to modify the chips performance. On a traditional 555 timer the control voltage input is located on pin 5 while on the 556 you would use pins 3 and 11 as I have here. By connecting the outputs of two 555 oscillators to these pins on the 556 we are able to use them to modify the frequency of the stepped tone generator.

You may notice in the video I play mostly with the left LFO knob. This is because in my experimentation I was able to illicit much more noticeable effects from the first oscillator connected to pin 3 of the Atari Punk Console. The second oscillator (connected to pin 11) only seemed to have a pronounced effect at fairly high frequencies. For this reason you may want to try switching the 500K pot on the second oscillator for something smaller like a 100K or 50K. Another option to increase the frequency range is to change out the 3.3uf capacitor for a 0.1uf cap.

Another thing you can do with this circuit to gain further control is to add a potentiometer to control the modulation of the LFOs on the Atari Punk Console. To accomplish this you can add a potentiometer in place of the 10K resistor at the output of the LFO oscillators. A 50K pot would likely work best for this.

Finally if you enjoyed this project I did build an Atari Punk Console back in the early days of this site with jacks for control voltage inputs. Feel free to have a look if you are interested.

 

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Kidtunes Keyboard – Demo Video

I just recorded a quick video of my Kidtunes Keyboard project and wanted to share it with you. This project has been a lot of fun and I recommend it highly. I can’t wait to get an output jack added on so I can run it through an amplifier and see what it’s really capable of.

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Basic Bends – Kidtunes Electronic Keyboard

I’ve been working on a new toy and I wanted to give a quick update on my progress with it. Today I’ve been working on a Kidtunes Electronic Keyboard which I picked up at Value Village. The Kidtunes electric keyboard is made by a Chinese company called Scientific Toys and though I wasn’t able to find an exact year I would assume based on the circuit that it came out in the early 2000s. The keyboard itself is a little odd as it has two octaves (from G to F)  but is missing the second F sharp. I guess they assumed kids wouldn’t notice. The toy is monophonic (only one note can be played at a time) but has two distinct voices. There is a sustained organ voice as well as a shorter cleaner piano sound. The Kidtunes keyboard also features a demo mode and a low-high volume control.

One thing struck me as odd on the circuit board of this toy. It looks like, though they have used a black blob IC, they manufactured it separately and then added it onto the board. This has left easy access to the pins of the IC where it was connected to the main board. Though the majority of these solder points are triggers for the keys it still allows a level of access which is rare with modern toys. Additionally all of the components outside the main IC are though hole which allows for fairly easy bending and modification.

The first thing I added to this keyboard was a simple pitch bend. To do this I located the pitch resistor and removed it. On this toy the pitch resistor was located immediately below the IC. The resistor I removed was 220K ohm so I replaced it with a 100K ohm pot and a 150K ohm resistor in series. While playing with the pitch bend I also noticed I could illicit some very interesting glitches by attaching one of the legs of the pitch resistor through a capacitor to the base of a transistor on the far left of the board. I wired this up through a switch and moved on to see what else was available.

The next two bends I found were fairly straight forward point to point connections which I wired through switches. The first (red wires) involved connecting one of the resistors on the board to the trace running across the emitter of the transistor I mentioned in the pitch bend. This bend seems to impact the sustain of the Kidtunes keyboard. By connecting these points all sustain is removed so that the keyboard sounds like an xylophone. The second (yellow wires) connects one of the trigger points to a resistor on the board. When the keyboard is in organ mode this has the effect of holding any note played indefinitely when the switch is turned. Further in demo mode this will cause a note to play repeatedly. This second functionality will be extremely helpful while searching for further bends as I will no longer have to keep pressing keys.

That’s as far as I’ve gotten with this one so far. If I am able to find more I will be sure to provide an update. Also I should have a video of this toy online within the next day or so.

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555 Based Piezo Trigger

I’ve always been drawn to drum pads and kits. They are lots of fun and offer a slightly more tactile method of control then rows of pots and switches. So today while I was playing around on my breadboard I was drawn to pull out some piezoelectric disks and start experimenting.  What I’ve come up with is a very simple drum trigger circuit that you can build and experiment with.

This circuit uses a 555 timer set up in monostable mode. A monostable 555 timer will output a square wave pulse whenever it receives a trigger pulse from the piezo disc at pin 2. The pulse output from the 555 can then be adjusted through the 500K ohm pot placed between V+ and pin 7. The output pulse is then sent into the base of a 2N3904 transistor which works as a gate between the audio source and the speaker. This means when the pulse from the 555 is high the audio will pass through the transistor and when the pulse ends and the 555 output goes low the transistor will block the audio from passing.

If you are interested in adjusting the pulse length beyond what is available using the pot this can be achieved by adjusting the electrolytic capacitor between pin 6 and ground. By lowering the value of this cap you can shorten the range of pulse lengths available. Conversely by increasing it you can access a longer range of pulses.

By setting up 4 or 5 of these piezo trigger circuits you could create a fairly versatile set of drum pads. Since the audio source can be switched out or developed further there’s a lot that you can do to expand on the acoustic possibilities of your drum kit. You can try experimenting with different oscillators, Filters, LFOs, White Noise Generators or anything you want.

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555 Oscillators in Series

I’ve been spending a lot of time lately playing around with 555 timer chips and wanted to quickly share my latest creation. This project uses four 555 timers each set up as a standard astable oscillator. I’ve then connected the output from pin 3 of each oscillator to the control voltage at pin 5 of the next subsequent chip. Essentially this means each 555 timer is working as an LFO for the next oscillator to it’s right. I also increased the size of the capacitor between pin 6 and ground of the two left-most oscillators in order to  lower their frequency.

I was quite pleased with the range and depth of sounds it produced however, it should be said that I built this as a proof of concept and it is not fully flushed out. I would be very interested to try a similar setup with a different waveform. I feel like this idea would really come into it’s own if used with a triangle or sine wave oscillator which produced a wider range of tones. I have also been experimenting, with some success, with adding capacitors between the output and control voltage inputs to smooth the square wave slightly and create a saw tooth pattern. Without an oscilloscope on hand however this is proving difficult to optimize.

This is also a circuit which can be easily expanded by adding additional oscillators and admittedly there is a little voice screaming in my head to take it to it’s logical conclusion. I expect in my near future I’ll spend a rainy afternoon stringing together as many 555 circuits as I can fit on my breadboards and see what I end up with. I’ll be sure to share the results.

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Young Scientist – 320 Project Lab


This past week I was taking my usual trip through my local Value Village thrift store when I came upon something really rather cool that I wanted to share with you guys. Tucked at the back of a shelf in the toy section I found this Young Scientist 320 Projects Lab. I was shocked when I opened it up to find this kit not only to be in working condition but that most if not all of the components were still present in the box, including the numerous IC chips (more on them later). I decided for 6.99 Canadian how could I lose and brought the project lab home for to try it out.

I’ve only been able to find very limited information on the 320 projects kit or the Young Scientist brand itself. For this reason I can’t say exactly when it was released or the products history but based on the “Laptop PC styled” case and the windows 95-esc graphics on the lid I would assume the kit came out some time in the mid to late 90s.

I have played with a number of other electronic kits through my life and generally have mixed feelings about them. Kits like Snap Circuits or many Radio Shack’s 200 in one, 150 in 1 ect. offer a great introduction to circuits and basic components, however they always left me wanting. Once you have completed the projects designed for the kit there is nothing left to do and the box finds itself gathering dust. Though the knowledge you gain through these projects is invaluable there is no easy way to transition from them into further electronics work.

The Young Scientist 320 Project Kit seems to have a slightly different philosophy. The usual spring connectors we know from Radio Shack kits are present but they are secondary. They are organized around a breadboard placed dead in the center of the kit. This kit uses standard through hole components the same as the ones you would use in any hobby electronics project. This means you can build and solder together any project from the kit onto protoboard and also build essentially any electronic circuit within the kit. Further within the instruction manual it encourages “Young Scientists” to expand their component collections and even gives some basic instructions for salvaging parts.

Another exciting feature of this kit can be found on the breadboard and that is the power supply. The power rail of this breadboard is split into 6 sections providing easy access to a full range of common voltages (1.5, 3, 4.5, 6, 7.5 and 9).

The kit also included a number of IC chips. Again these are standard through hole components the same as you would use in any hobby project. There was no surprise in finding the hobbyist heavyweight 555 timer along with some standard op-amp and amplifier chips but I was pleased to discover the set also contained a fairly complete array of digital logic gates, counters and decoders. The inclusion of these digital components allows for some extremely complex builds towards the end of the project book including Function Generators, Logic Probes, various games and Octave Generators (just to name a few).

As an adult with hobby electronics experience I am loving this kit but I should say in closing that it is not for everyone. The decision to use standard through hole components and a breadboard makes this a far more versatile project lab than others I have worked with and allows for the construction of far more complex projects but it is a double edged knife. If you are an absolute beginner to electronics the smaller more fiddly parts can be confusing or challenging to work with and the level of difficulty in many of the projects could be discouraging. For this reason this is lab is likely better suited to someone with some knowledge of electronics, components, resistor codes ect. Still, If you have some basic knowledge or are up for the challenge, a project lab like this one can be a great way to build your skill level and play with hundreds of new and interesting circuits.

 

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PSR-6 Demo Video

Hi Everyone

I just wanted to upload this quick demo video of me playing around with my PSR-6. I’m planning on reopening this project to expand on it in the next few weeks so I should have more updates soon but in the meantime this will give you an idea of the kinds of noises this thing can make.

Patch bay – Yamaha PSR-6

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Data Patch Bay – Yamaha PSR-6

circuit bending

While browsing some circuit bending sites some time ago I found an excellent tutorial over at Circuit-Bent.net for adding a patch bay to a retro Yamaha Keyboard. The tutorial dealt with the PSS-170, 270, 140 and SHS-10 but not having any of these models on hand I wanted to see if I could apply the same technique to the a PSR-6 I recently scooped up on the cheap at a local pawn shop. Finally this past week after the arrival of a big bag of banana plugs from E-bay I decided to give it a try.

– I also came across a very helpful forum post on Electro Music from another circuit bender (user name Dnny) who converted this mod for a PSR-6, It is definitely worth a read if you are attempting this bend.

circuit bending

To understand this bend you have to understand a bit about the inner workings of these keyboards. The PSR-6 (and many others of the era) operates using two primary IC chips. The first of these is the Yamaha XE323B0 CPU chip. This chip is easily identifiable as it will usually be the largest chip on the board and has a huge number of pins (I believe around 60). This CPU chip is the brain of the keyboard. Beside the CPU there is a smaller 18 pin FM synthesizer chip (the YM2413) which is responsible for actually creating the audio signals you hear out of the keyboard.

If you study the back (trace) side of the circuit board you will see there are 8 traces which travel directly from the CPU to the FM synthesizer chip. These 8 traces carry instructions from the CPU to the synthesizer chip and tell it when to make noises, and what noises to create. Further each separate pin carries information on a different aspect of the sound. These 8 traces are what I will be hijacking with this bend.

circuit bending

The first step I took was to cut each of the traces running between the CPU and the FM Synthesizer chip of the PSR-6. This will interrupt the normal flow of data. These circuit boards are very ruggedly made (as opposed to some more modern boards) so you may need to cut across them several times with an Exacto knife. Use a multimeter to confirm there is no connection between the two sides once the traces are cut.

Circuit Bending

Next up comes the really fiddly part. I soldered lengths of wires to each pin on the CPU and each pin on the FM synthesizer. I used yellow wire on the CPU and blue for the synthesizer so that they were easily identifiable. It is very important at this point to keep the pairs of corresponding wires together. I used pieces of painters tape to temporarily attach the pairs of yellow and blue wires together and numbered them in order from 1 to 8.

circuit bending

Once I had drilled and mounted the components for the patch bay I was ready for wiring. I soldered the blue and yellow wires to the middle and lower lugs of a row of switches. I then ran wire from these switches to two rows of banana jacks. All of the CPU connections I ran to the top row of jacks and all the synthesizer connections to the bottom row of jacks.

From here I closed up the keyboard and powered it up. To my delight it worked great. When the switches are all in the up position the data lines are connected and the keyboard works the same as it did without any modification. However when you flip the switches or connect any of the red jacks to any of the black jacks… things get weird.

Circuit Bending

When you are getting started with this patch bay it can be a little intimidating. It will crash and it will spew loud garbled noise, don’t be discouraged. You will also find strange, new and truly bizarre  noises you never knew the PSR-6 had in it. A good way to get your feet wet is to choose any instrument on the keyboard. flip down the second switch and then change to a different instrument. The turned switch will stop some of the information regarding the new instrument from reaching the FM synthesizer and you will be left with a strange hybrid of the two voices.

The more I play with this keyboard the more fun I have. Slowly I’m beginning to understand what each data line controls and I’ve been able to create more and more interesting patches. One surprising thing I’ve found is not all but many of the patches are repeatable allowing you a level of control over the noise I didn’t expect. This makes the device quite viable for live performance.

Now that I’ve gotten my feet wet with this bend I’m incredibly interested in taking it a step further. I’ve seen other circuit benders set up LED’s associated with each data line allowing you to see the data traveling through each connection. This seems like it would be extremely helpful in developing your understanding of what each connection controls. I’m also going to do some tests injecting a square wave oscillation into the data points to see what kind of results this elicits.  Finally I’d also be interested to try running the data through an inverter or other logic gates. If I have success with these tests I will create a second post detailing what I’ve found.

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LM386 Modifications – Yamaha PSS-30

circuit bending LM386 modifications
While completing my first set of mods on my Yamaha PSS-30 I noticed that the internal amplifier driving the mini keyboard was a 386D amplifier chip. This chip has an identical pin out and seemingly identical function to the popular LM386 which gave me some ideas for possible bends I could try. If I was able to apply some common modifications or adjustments which work with the LM386 in amplifier applications like the LM386 guitar amp I may be able to further expand the versatility of the instrument.

circuit bending

The first modification deals with the gain of the amplifier. If you’ve worked with LM386s in the past you may already know that the gain of the amplifier is set using pins 1 and 8 of the chip. Essentially by placing a resistor (usually 1 ohm – 10K ohm) and a capacitor (typically 10 uf) between these two pins you can set the gain. The higher the resistance of the resistor, the lower the gain. Upon inspection of the circuit I could see this is exactly how this 386D chip was set up. Pin 1 is connected through a 10 uf capacitor, which connects to a 1.1K ohm resistor (immediately to the left of the chip) And then to pin 8 of the chip. In order to replace this system with a variable gain control I removed the 1.1K resistor and replaced it with a 5K ohm potentiometer. By reducing the resistance you can get a slightly crunchier and more distorted sound, and by raising the resistance you can get a cleaner more polished sound. Note the gain level will influence the volume of the output so you will need to compensate for this either at the volume control added in Part 1 or at your mixer/amplifier.

circuit bending

While I was under the circuit board attaching the leads for the gain pot I also connected a few more wires for use with my second mod. I connected the first wire (yellow) to pin 1 (gain control pin) and two blue wires to pin 5 (output). These will be used for the second modification I had in mind. This is a slightly less used LM386 circuit modification but still one which is fairly well documented. By sending a signal from the output pin (5) through a small capacitor and resistor to the gain control pin (1) you can create a bass boost effect. To accomplish this I attached the first blue wire to a switch on my panel. I then ran it through a 0.1 uf capacitor and a 10K ohm resistor. I attached the yellow wire to the other side of the resistor completing the circuit. Now by flipping the switch you connect the bass boost circuit.

Though the bass boost is audible I am not overwhelmingly impressed with it. It is far from the thumping low end I was hoping for. This may be a limitation of the device itself but I feel like further experimentation is needed. I will be going back in to experiment with some other cap/resistor values and other circuit options to see if I can get a better effect. I will report back here if I find better results.

circuit bending

The second blue wire I connected through a resistor to an LED and tucked it behind the circuit board. Because I used a transparent panel this creates a cool back lit effect and since it is powered from the amplifier output it pulses along with whatever is being played on the keyboard.

That about raps it up for the PSS-30 for the time being. I really love the small form factor of this device and would love for it to make it’s way into my regular instrument lineup. In spite of this circuit being a bit limited as far as bend points and options, I still had a lot of fun and got to try out some interesting new things on the circuit. I’m going to keep this device in the back of my mind as I work on other projects and hopefully I can return to it down the road with some new ideas to further mangle it’s square wave outputs. That’s all for tonight but thanks for reading and happy soldering!

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