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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Tone Control and Line Out – Yamaha PSS-30

The thrift store gods smiled on me again this past week. During one of my usual trip to my local charity shop I found a Yamaha PSS-30 marked at 5 dollars. Not only was this tiny keyboard still in the box, it looked like it had barely been played since it’s manufacture back in 1987. I happily scooped it up and brought it home to investigate.

Now after looking inside this keyboard and spending some time online I found unfortunately the PSS-30 may not be the holy grail I had hoped it would be. Many of the Yamaha Keyboards of this era (along with many of the infamous Casio SA keyboards) contain two primary chips. The first is a synthesizer chip (usually an FM synthesizer) and second a CPU which monitors the inputs and digitally controls the synthesizer. This allowed some extremely interesting bending by cutting or crossing the data lines to modify the signal reaching the synthesizer chip.

PSS-30 circuit board

Unfortunately the PSS-30 in an effort to cut costs and save space is built to run on only one IC chip. This means the single YM2410 chip monitors the inputs and generates the audio signal internally leaving us unable to access the data flow. That being said I still wanted to have some fun with this very cool vintage keyboard.

I wanted to start this project as I do most of my builds, By adding a line out. It was also fairly important to me to add an analog volume pot along the line out. The reason for this was simple, This keyboard uses a basic digital volume control which is extremely loud and distorted on the maximum setting. Unfortunately whenever the device is powered off and back on the digital register for the volume setting resets and it returns to this obnoxiously loud setting. With the addition of an analog volume pot I can set the volume where I want it and leave it there without having to worry about it resetting.

To add the line out I cut the speaker lines. I wired the positive speaker line to the top pin of a 100K potentiometer and the ground to the bottom pin. From here I connected the tip tab of a 1/4 inch jack to the middle pin of the pot and the ground from the jack to the bottom pin. This functions as a simple voltage divider and allows you to adjust the amount of the signal which reaches the jack.

Yamaha Circuit Bent cutting

Since the keyboard itself is so small, In order to create room for the controls I had to remove the speaker altogether. Initially I attempted to drill holes for my components into the slatted plastic speaker cover but things quickly got messy and it became obvious that wasn’t going to work. Instead I used my trusty rotary tool to cut out a rectangle where the speaker had been and covered it with a square of plastic I cut from an old DVD case. This will be my control panel for the time being. Once I have the device working how I’d like it I will likely replace this plastic panel with acrylic or steel to give it a more professional look.

Tone COntrol

Additionally as something of an experiment I built a small two knob tone control circuit into the line out. This is a circuit I picked up from an excellent article over at Nuts and Volts (Fig 12). The circuit essentially functions as an adjustable low pass and high pass filter. Since the circuit itself is passive I did experience some attenuation but not enough to become an issue. Since this keyboard uses only square wave audio the capacity of these filters is somewhat limited. You can make some adjustment to the sound but if you limit either end too far the sound will become very flat and tin-y.

I also noticed that the PSS-30 uses an LM386 as an amplifier meaning that I can try some common LM386 amplifier mods on the circuit as well. I will be posting again shortly to let you know how they went but in the interim thanks for your time and happy soldering!

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Danelectro BLT Slap Echo – Guitar Pedal Bending

Guitar pedal circuit bending

After getting my feet wet with my Danelectro T-Bone Distortion Pedal I wanted to keep up the momentum. My next victim would be my Danelectro BLT Slap Echo mini pedal. Like the T-bone the Danelectro BLT Slap Echo pedal is an extremely low cost and relatively simple pedal which makes it a perfect candidate for circuit bending.

guitar pedal circuit bending

The BLT Slap Echo consists of two circuit boards. The lower board (brown) is dedicated to driving the inputs and operating the foot switch. This lower board is identical to the one found on the T-Bone Pedal. Because it is not involved in effects creation I will be ignoring it while circuit bending.

The upper green board is where the magic happens. The upper board is driven by a PT2399S Digital Delay Analog Echo chip which is where I found the majority of the bend points. The second smaller IC is a simple TL072 op-amp which I largely ignored. One thing you will notice about these Danelectro mini pedals which makes them extremely pleasant to work with is that there are unused solder points throughout the circuit which can be easily connected to to create bends.

guitar pedal circuit bending

After probing the circuit board and some experimentation I settled on the points shown above. I soldered leads to each of these points using different colors to distinguish the different bends. Once the soldering was completed I also applied some glue to each solder point to hold the wires in place. This glue will keep the wires from tearing off the (admittedly weakly constructed) solder board and also prevent them moving around and touching other points.

From here I ran the wires out through the hole in the pedal case I had drilled and through the lid of the container I would use to house the switches. This container will likely be a temporary housing as it lacks the durability you need in a pedal. Down the road when I have the materials available I will create a post where I rehouse both the T-Bone pedal and the BLT Slap Echo into their own custom pedal boxes.

The first bend here is made by connecting the green and blue wires. This produces something of an infinite echo. rather than the echo decaying over time as it normally would it will continue until the bend is disconnected.

Next I used an on – off – on switch to connect the blue wire to either of the yellow wires. This bend creates a crunchy distorted echo effect. One of the yellow wires will give you a more treble base distortion, and the other will give you a more bass distortion. I have not tried it yet but I would be interested to know what happens if you wire the blue to the wiper on a potentiometer with the yellow on either side. You may be able to tune the pitch of the distortion this way. I expect I will attempt this when I rehouse the pedal.

Third I connected the red wires together. This is probably my favorite bend on this pedal. It is more subtly then some of the others but creates a really satisfying slow reverb effect that I really love.

The final bend was to connect the black and green wires. during testing this created a nice white noise effect behind the pedal output. Unfortunately though now that I have wired everything up it does not appear to be working. I’m not sure if I mixed up the solder points or if something came disconnected while I was closing up the circuit, but I will do some troubleshooting and provide an update if I can get it working again.

Guitar pedal circuit bending

From there all that’s left is to box everything back up and get playing with it. I will be creating a video within the next few days to demonstrate the bends on both my T-Bone Distortion Pedal and this BLT Slap Echo pedal. Overall I’ve found these Danelectro pedals to be really rewarding and great way to initiate myself into the world of guitar pedal bending. Hope you all enjoyed and have a great week.

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Danelectro T-Bone Distortion – Guitar Pedal Bending

guitar pedal circuit bending

I decided to try something new this week. I have a couple old guitar pedals laying around my shop and I wanted to open them up and see what I could do as far as circuit bending them. The first I bent was a Danelectro T-Bone Distortion mini pedal. I chose this as my first because it is small, relatively uncomplicated and most importantly cheap. I have a second Danelectro mini pedal (A BLT Slap Echo) which I will be bending next but before I do I wanted to get some practice with pedal bending. Also this distortion pedal will give me a better understanding of how these devices are put together as the two pedals are constructed very similarly.

After opening the T-Bone Distortion pedal up my suspicions about it’s simplicity were confirmed. The pedal is made up of two separate boards connected by a short ribbon cable. The lower board (brown board in this image) appears to primarily handle the functionality of the switch and the inputs and as such I will be largely ignoring it. A quick look in my BLT pedal confirmed that this lower board is shared between all pedals in this series and is therefore not involved in the effects production. I will be focusing my efforts on the upper (green) board.

The effects board on the T-Bone Distortion pedal appears to be built around an LM324 quad op-amp chip. This chip is essentially four op-amps (LM741s) arranged on a single chip with shared power and ground. Another helpful thing I found with this board is that there are numerous unused solder points throughout the circuit which made experimentation and modification extremely easy. Likely this board was developed to serve multiple purposes or be used in multiple pedals depending on which components or points were used.

By feeling around on these unused solder points I was able to find a number of areas which created additional effects though the majority of these effects were very similar to each other. In the end I decided to keep things simple for this project and settled on three soldering points. When these points are used in combination they allowed me to create two new effects which I found interesting and fairly unique. By connecting the blue wire shown above to either of the green wires (through a potentiometer) you can create these effects.

For the first (using the green wire on the left side of the board) I used a 200K ohm potentiometer. This creates a high gain bass boost effect. As you get closer to 0 ohms of resistance this boost devolves into a crunchy noisy mess and the melody for your guitar (or other inputs) is all but lost. That being said if that is the effect you are after it is quite pleasing. As you raise the resistance up close to 200K though you can get a very nice (if still a bit crunchy) bass boost added onto the melody you are playing.

The second bend is a bit harder to describe. For it I used a 10K pot and added a 27K resistor in series. With this bend the pedal will die if you lower the resistance below about 25-26K so the extra resistor stops this from happening. with no inputs going to the pedal this bend will create a smooth square wave oscillation, the pitch of which can be adjusted with the potentiometer. Once this is connected with inputs going to the pedal though things get a bit strange. The oscillation and the audio playing through the pedal begin to modulate each other and create some very fun and interesting effects.

Since there is very little free space in these pedals I opted to run the wires out to a small container I had on hand. I drilled a small hole in the side of the pedal and ran the wires out through there prior to attaching the switches and pots. This is not a very permanent solution and I expect I will be re boxing this pedal down the road. That being said it works for the time being. To protect the wires I loosely wrapped them with electric tape (heat shrink tubing will give a cleaner effect if you have some on hand) and created plugs for the holes on the pedal and box using hot glue. This will prevent the wires from being tugged which could disconnect the solder points. With that my Danelectro T-Bone Distortion was ready to play!

That’s it for today, I hope you guys enjoyed this project. Once I have finished the BLT echo pedal I will upload a video showing off the effects. Until next time, happy soldering!

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