Category Archives: How To…

Modify Mattel MindFlex to Contol Synthesizers with Your Brain Waves!


Robert Schneider is a musician and record producer best known for his involvement in The Apples in Stereo. He is also a student of mathematics, occasional experimentalist, and a GetLoFi reader! The other day he shared this simple yet elegant mod for Mattel MindFlex.

This toy device is designed to read brain wave activity via a headset which allows the wearer to control a fan that levitates a small ball.  The brain wave activity guides the fan and the ball around an obstacle course. The  modification allows the wearer to use brain waves to control and change the pitch on a synthesizer via CV (control voltage).  Schneider removed the DC power that goes to the internal fan and routed that to an added 1/4 inch output jack which he connected to a synthesizer.

In his own words Robert details the modification in the following video.[youtube][/youtube]

Control Voltage Output from 555 Timer Circuit

After successfully building the 555 timer circuit the next obvious step is to use this oscillator as a Control Voltage Source. The only problem is that the output from Pin 3 is a square wave either on or off. While great as a Pulse Out that can be used to power another circuit, it gets fairly boring as  a CV source. What we need do is add a few extra components to give it that Warble.  First the signal passes through a 10K resistor to limit the current,  then charges the capacitor in turn discharging to the Ground during the Low phase of the 555. The output voltage is now in the form of a ramp and can be used as a CV.

To Connect the 555 LFO to the APC you can use the same circuit consisting of 10K Resistor and 10uF cap connected to the Ground. It is possible to play around with values, increasing the Capacitor value and also adding the potentiometer to make the Ground draining slower. The output of the LFO can now be connected to Pin 3 or Pin 11 on the APC circuit board. It is also possible to use separate LFO circuits going into both 3 and 11 as well as Syncing those together.

The above circuit is just an example to get some experimenting off the ground, feel free to modify the basic idea.

Here is a short example of the circuit in action:


Kaoss Pad Pitch Modification w/Internal Controls

David M. just sent us useful information on how to add internal pitch controls for both Kaossilator and the Kaoss Pad, below are his words of wisdom…

After reading about the GetLoFi Tutorial for 1799 oscillator circuit mod on the KORG Mini KP/KO and with a few of the LTC Modules on hand I decided to give it a go on a brand new Kaossilator. The conversion took about 45 minutes to do, but the results just blew me away. A real transformer for this instrument.

Looking over the comments  at the GETLOFI site, it seems that nobody found a good place for potentiometer placement, all being too big. It took several orders of varied thin potentiometers from the usual suspects like: ebay, digikey, and mouser to locate a pot capable of doing the job.

Mouser ended up with the goods (digikey has a 16mm Panasonic pot in their latest catalog, but it is not available.)

You will need to fab a piece of thin metal, then bend and solder it to the pot in-order to mount it securely.

The piece of metal I used was from shielding of an old stereo, cut into an 8×45 mm strip. There also needs to be a 19mm gap in the U-shaped bracket to keep it from bumping into the components on the overhead board.

The hole for the roller is 1.5x13mm and the top of the hole is flush with the inner front-side of the case. A small jeweler’s file is helpful in shaping the hole. A small portion of the touchpad backing plate has to be notched out to make room for the pot.

Note the 100K resistor used for changing the range of the 500K Potentiometer to 100K, giving it a nicer operating frequency without going too Low.

A 10K trimpot was added to the circuit to dial in the value for preventing a crash (somewhere around 7.5K ohms. ) the trace must be scraped on the outer edge of the LTC board to fit the trimpot in, as well as the thin bridge on the pcb trace between the trimpot.

Since you have to take the plate off, this is the perfect chance to try Nebulagirl’s touchpad picture mod and how about a sporty paint job?

I used a different point for the negative hookup for the circuit, than listed in the tutorial. (second picture) This location allows you to use the dc adapter jack as well as battery.

Now before you do this, many people warn against wall-wart power on bent instruments.
What I use is a “battery bomb,” basically a battery holder with a power plug pig tail (an idea from Q.R. Ghazala’s book.) When I gig with these instruments, I carry one of these in my pocket for a quick back-up for failing batteries. Good luck.

by David M.

Links: GetLoFi Shop, GetLoFi LTC Module Kits, Previous Kaossilator Articles.

Nintendo Gameboy Pitch Mod with a Switch

The Gameboy Pitch and the Pro Sound modification has been covered previously. However several readers asked about a relatively simple feature to select between the LTC Module Pitch control and the Normal Gameboy Speed.

To do this correctly you need the LTC Module or the GameBoy Kit ( now including the switch) from the Shop. The Switch must be high quality with smooth movement switch, otherwise any resistance or noise in the switch will crash the Gameboy during the selection. The rest of the hook up could not be easier, simply cut the output wire in half and insert the switch in series as seen in the above photo on the yellow wire. Black and red wires are standard Power connections to the LTC. Mounting of the switch will be the hardest part of the procedure. Make sure that everything lines up and the Gameboy will close in the end. Good Luck.

Simple 3-Channel Stereo Mixer with VU Meter

Dear Readers, please welcome a new contributor Colin Merkel. His projects include an impressive built from scratch micro controller based looper and now a simple Stereo Mixer.  I’m sure this will be useful in circuit bending applications. It is worth noting that the project below was built from spare parts and could be done much smaller if needed. – CM

My name is Colin Merkel, and recently I have been annoyed by the audio setup in my room. I have some really awesome speakers, but they are usually attached to my computer-when I want to plug my iPod in, or anything else for that matter, I have to fiddle around with 3 different cables – very frustrating!

So, to fix my problem, I put together a simple 3 channel stereo mixer.


As you can see from the photograph, there is an analog VU meter, one volume knob and mute switch per channel, and a master volume control in the form of left/right level sliders.


The electronics behind the system are extremely simple- in fact, I used only a single LM324 quad op-amp, some resistors, and some diodes. The entire circuit runs off of a 12V DC wall wart power supply. Shown below are poorly-drawn schematics for the left and right channels.

As a possible improvement, I may add a headphone jack on the front so that you it would be easy to put all the mixer output through headphones. Here are some photos from the build:

Breadboard layout
Testing on the breadboard!
Soldering the circuit...
Completed circuit
Completed circuit
Have to keep good notes...

Anyway, the mixer was an easy build that managed to make my audio system a little bit more awesome. Thanks for reading! If you have any comments or questions, feel free to ask.

Excellent Tutorial on Building Logic IC Oscillators from Beavis Audio Research

The Beavis Audio Research Group just added a great overview for building CMOS Oscillators and LoFi Synths. Starting with your basic oscillating Hex Schmitt Trigger and finishing with a Heterodyne Peyote Space Explorer. The tutorial has clear examples with valuable pieces of information for adding LFOs, Rate LED Indicators, Line Level and Volume control as well as component values for good frequency ranges. Excellent work!

DIY Modular Sequencer Circuit Examples

by SailorMouth

So you have amassed a pile of circuit bent toys. What are you going to do with them now? Each creation has its own control interface — pitch knob, distortion and glitch switches, body contacts, and/or LDRs — and of course, the buttons to bring the noise. Naturally, though, you can only play so many toys at one time. Enter the modular sequencer, which will assist in making some sense of balancing control.

I chose to approach this project from the view of low-cost DIY because I have more time than money. With my time, I have been able to learn new things, which have grown to their own new ideas. I have kept the cost of working through new designs low, spending as much on components as I would for bending a piece, anyway. I am on my fifth sequencer design, and through all of them, the adapter interface to the bent toys has stayed the same. It is simple and expandable. It can work on basic 2 wire buttons and matrix buttons. The toys all have the same connection method, but the control circuits have changed from step to programmable to various pseudo random designs.

I will break this down to prepping the toy, adapter interface, control circuit, and some of what can be done. This will get somewhat technical, but it can be done with patience and rereading confusing parts. I’m also happy to answer questions. All though I refer to toys this can be applied to instruments, sound circuits you build, or anything with buttons that make sounds.
Continue reading DIY Modular Sequencer Circuit Examples

How to add Getlofi LTC1799 to Casio Sk-1

by Spunkytoofers

I’ve gotten several requests on how to hook up the Casio Sk-1 with a Getlofi1799 Oscillator so I’ve quickly drawn up a diagram for hookups. According to other sources the clock input can be directly injected without cutting the trace. That may be possible but there are bootup problems if the clock isn’t at it’s original setting so you may need to add a switch regardless. The note about the optional 500 ohm resistor is only if you notice your sk-1 is now out of tune for wiring to the clock lines. this should drop pitch to a range where you can fine tune the keyboard back to A=440.  Access to the fine tuning is available thru the bottom plate of the sk-1.  Click thru on the pictures to get an exploded view of the diagram.

GetLoFi 4017 Sequencer Kit Implementation

The 4017 Sequencer Kit has been available for quite some time, however the documentation has been rather lacking. Aside from that fact that it makes a great 8 step trigger circuit  we have not even tried it as a Control Voltage (CV) source until now.

Go get started the Sequencer circuit board needs 3 Input connections. Ground ( Black ), Positive Voltage ( Red ), and Clock Input (Blue ).

The Tempo to advance one step in the sequence is provided by a 555 Timer Module. Positive Voltage and Ground connections are shared.

The Simplest circuit demonstrating the most basic operation is an LED used to preview or indicate the steps in the sequence.  Negative side of the LED must be connected to the 4017 board Ground and the Output pad will serve as a source for Positive Voltage. A resistor is needed to limit the current, typically anything between 100 – 1,000 Ohm will do fine. When the step is set to High at the specific pad the positive voltage is sent out lighting up the LED. Note that this is the basis for using the sequencer as a triggering device for other circuits.



Circuit Bent Kaossilator with Internal Controls

Previously on GetLoFi we covered adding of the LTC Precision module to control the clock speed of the Kaossilator, thus pitching the device up and down. The only snag with the mod was not having the potentiometer mounter internally. Now that problem has been solved with a daring modification to the device.

There is plenty of space for the potentiometer if you remove an unused part of the output circuit board. The RCA jack board is the same for KP and the KO, however KO does not use the Input side. Carefully remove that section with a Dremel Cutoff disk. You may use the above image and black line as a guide. However do so at your own risk! The RCA jacks were tested and appear perfectly fine on my unit.

Remaining section is shown above.

Once the potentiometer is seated a slight modification to the case is needed in order to properly shut.  Cut away several of the plastic ridges on the inside of the case as well as the plastic holder of now missing Input section. Dremel Sanding cylinder disk works well.

Last step is to drill a hole in the aluminum for the potentiometer shaft. Measure the position of where the hole will go and use ridges as a center guide. Making the hole slightly bigger will help to reassemble the device.

Note that there is a 100k resistor soldered in parallel with the 250k potentiometer used to control the pitch. This is done prevent the pitch from dropping too low and it also gives a very nice usable pitch range.

The kit which includes the potentiometer, wire, and the LTC board is available from the GetLoFi Shop. Good Luck.