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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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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Build A Simple Gate Sequencer

Gate Sequencer

For the past week or so I’ve been working on building a 4017 based matrix gate sequencer. I originally started thinking about this project after purchasing a set of Kawasaki electronic drum pads from a local thrift store. I wanted to create a tool I could use externally to trigger the drums in a continuous loop. As I began to design This build though i began to realize it’s full potential went well beyond that.

As this sequencer goes through each step it outputs a voltage (approximately 5V) at the top most pin on the matrix. By connecting this top pin to any of the 6 pins directly below it you can send this signal out through the associated output on the side of the gate sequencer. Because these signals are being sent at approximately 5V they are perfect for switching low voltage transistors such as the 2N3904 (essentially allowing it to turn on or off an electronic switch wherever you send it). By using these outputs to switch on or off transistors they could be used to trigger a sound from a toy, gate an oscillator, turn on or off a channel on a mixer, trigger an envelope or anything else you desire.

Click here for details on setting up triggers in a drum toy

Gate sequencer 4017

I’ve also included some basic controls common to more traditional sequencers like the Baby 8. These include a rate control to adjust the clock speed, a hold switch which pauses the sequence, a step selector switch which allows you to select how many steps the sequencer goes through before restarting and a clock out for syncing other sequencers or circuits to the gate sequencer’s clock rate.

Parts List:

  • 555 Timer IC
  • 4017 Decade Counter IC
  • 2 – 4.7 K ohm Resistor
  • 1 – 100 ohm Resistor
  • 200K ohm potentiometer
  • 1 – 10 uf Electrolytic Capacitor
  • 1 – 0.1 uf Ceramic Capacitor
  • LEDs (one for power and one for each step)
  • 1N914 Switching Diodes (One for each step)
  • Rotary Switch (number of positions equal to number of steps plus 1)
  • Toggle Switch – power
  • Toggle Switch – hold
  • Hook up wire (lots)
  • Ribbon Cable (Strands equal to number of steps)
  • Proto-Board
  • Clock out jack (I used 3.5 mm headphone jack)
  • Ground Connection Jack (I used banana)
  • 6 – Output jacks (I used bolts but banana jacks are ideal)
  • Matrix connections (I used pin headers but you can use whatever you have available, requires 1 out and 6 in per step)
  • 9V battery clip

Schematic:

This is the schematic I drew up while building the gate sequencer. For simplicity sake I did not draw out all of the steps but they will each mimic the first two shown on this schematic. Bear in mind though that the 4017 output pins do not go in order, make sure to check the pin out diagram to make sure you are setting up the steps in the correct order. For 8 steps you should be pulling from pins 3, 2, 4, 7, 10, 1, 5 and 6 in order.

I wanted to mention as well as it is not clear on this schematic. If you are using fewer than all 10 steps from the 4017 counter you will need to wire the output of the next pin higher than the ones you have used to the final position of your rotary switch so that the counter resets after going through the steps you have used rather than the full 10. For example my gate sequencer uses 8 steps (outputs 0 to 7 on the 4017) so I wired output 8 (pin 9) to the final position of my rotary switch.
AND gate for gate sequencer
If you are using this device to trigger circuit bent toys you may also run into an issue where you are not able to trigger the same noise for two consecutive steps. This is because if you send the signal to the same output for multiple steps the output will remain high rather than sending a pulse for each step. I was able to find the fix above from Peter Edwards of Casper Electronics who used it in a similar project he built a few years ago. In order to correct this you can place an AND Gate on each output and send the clock pulse into the second input on each AND gate as shown above. This will cause the output to pulse in time with the clock when the signal from the matrix stays high for multiple steps.

The Build:


The first step of the build was to populate the circuit. Following the schematic I had created while testing and designing my gate sequencer I placed and soldered all of the on board components. I also used a number of short leads to put the steps in order on the board so that I could work with them easier going forward. One thing I want to mention is the row of diodes shown in the above picture were actually removed and placed on a secondary board (more details to follow) to simplify the finished product.

At this point I also mapped out the surface of my project box and populated the off board components (switches, knobs and LEDs). Due to the number of components on the box I used a piece of graph paper cut to the size of the surface to plan the device locations then used a pin to mark each one through the paper. From here I drilled the holes for the larger components and secured them in place.

pin headers

Due to the sheer number of connectors required to build the matrix I was not able to use banana jacks (which would have been ideal). What I did have on hand though were a number of male to female jumper cables and a pile of pin headers. I cut 8 of the female heads for the top posts and used individual pin headers for the connections. To mount the individual pin headers i ran fairly high gauge solid core wire through the holes and soldered them to the short ends of each pin header. Next I pulled the wire back down the hole until the plastic guards on the pin headers sat securely against the top of the box. To secure them I poured a substantial amount of hot glue onto them from the underside of the box.

gate sequencer ribbon cable

In order to limit the rats nest I foresaw forming between the top of the box and the main board I used a small scrap piece of proto-board as a junction. From here I ran all the connections needed for each step. The ribbon cable shown here is attached back to the main board (orange is step 1 through to black for step 8). From the board there is an orange cable for each step to go to the rotary switch (attached to the reset pin), a green wire to connect to the LED for each step and a red wire to go to the top pin of the matrix for each step. Note the red wire is after a diode on each step while the orange and green are before it.


Here is a picture after each wire has been soldered to its place on the back of the lid. I also used hot glue to attach the small proto-board to the lid of my gate sequencer. Make sure you test all of the connections thoroughly prior to gluing it down. Check for any bleed between steps and that all the solder connections are strong. Once you glue it down it will be very difficult to modify.


I connected all of the pins on the matrix (excluding the top row) in rows and connected each row to the corresponding output on the side of the box. One more coating of glue and I was ready to make the final connections. First I connected the ribbon cable to each of the 8 steps on the main board. Then I worked my way around the components which needed to be connected to the main board. Once everything was connected I wired up the battery, power switch and power indicator LED. I secured the battery with some Velcro and after some brief troubleshooting (There was a faulty switch I had to change) it was ready to go.

I am currently in the process of setting up trigger bends on my drum pad. Once they are completed and running smoothly I will have another article up describing how you can use your new gate sequencer to trigger noises from circuit bent toys  and down the road you can expect to see me using gate and trigger voltages to control a variety of other devices. Within the next week or so I should also have a demo video of this device uploaded for you to check out.

Thanks for visiting and happy soldering!

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Voltage Controlled Atari Punk Console

Atari Punk Console (APC) complete 2     When I first started working with DIY electronics and synthesis I seemed to get the same advice everywhere I went. Every forum, blog and site I visited recommended the same project, The Atari Punk Console, and after building a few I can understand why. The Atari Punk Console (APC) is a simple yet rewarding project for beginners. With fairly limited parts it functions as a very basic standalone sound synthesizer but also has the capacity to be modified and controlled in a variety of interesting ways. This project is a great way to develop more experience soldering and circuit building and will serve as a platform as we begin to explore control voltage modules.

Click here to get started!

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