ATTiny44 Guitar Effector

A DIY ATTiny44 based guitar preamp+effector. All the audio processing is done digitally on-board. So it is definitely not a HiFi system, but something you can definitely have fun programming. You can program the audio properties in Arduino IDE and create mobile apps that talk to the module for remotely controlling the effects.

This instructable project requires a milling machine to create the circuit as well as SMD components, but if anyone is looking for a more accessible option, please check out this Arduino based version: https://www.instructables.com/id/Arduino-Guitar-Ef...

The circuit for the effector will be made using a CNC milling machine. I used a Modela but anything similar will work. The list of material required will include:

• LM386 (I used a DIP chip but SMD will make it more compact, while the traces need to be changed)
• ATTiny44
• 4 x 10k resistors
• 1 x 1k resistor
• 1 x 255k resistor
• 1 x 5 ohm resistor
• 1 x 0.1 uF capacitor
• 1 x 2.2 uF capacitor
• 2 x voltage regulator
• 1 x 6-by-1 male connector
• 1 x 3-by-2 male connector
• 2 x 2-by-1 male connectors
• 2 x 3-by-1 male connectors
• 1 x 3-by-2 female connector
• 1 x 20 MHz crystal

There is redundancy in the schematics since I designed it for many other purposes. FTDI connection (6-by-1) is not very necessary since only two pins we need are Rx and Tx. If an SMD version of LM386 is used, the 3-by-2 female connectors are not necessary.

Components needed outside the circuit board are:

• 9V battery connector
• 10k potentiometer (a big one with a knob)
• 220 uF capacitor
• 1/4" male audio connector
• 1/4" female audio jack
• 1/8" female audio jack
• Sparkfun Bluetooth Silver Mate

I used the png file above for routing the board. Depending on your setup, you will need to convert the file to machine code accordingly (eagle project for further modification is attached as well). In the png file, the outer border is through-cut, and the traces inside are only to remove the copper layer.

Note that there are two boards in the png file. The one in the left is the main circuit board with the microcontroller, where the one on the right is to have a separate voltage regulator for the Bluetooth module. It helps with reducing noise.

Once the circuit is completed, it is soldering time. The components placement can be found in the schematic (png or eagle) and in the picture above.

The final step for the circuit is to add audio connectors, a volume knob (potentiometer), a battery, and the Bluetooth module. The connections are illustrated above in the picture. I used female to female jumpers for the connection, but soldering cables directly to the circuit board (without connector pints) will make it more compact.

Note: I also added a capacitor between the knob potentiometer input and ground pins, and a potentiometer at the input stage for controlling volume. These are up to experiment and preference.

Download the arduino code and upload to your ATTiny44. Detailed instruction on how to program ATTiny can be found here if needed: http://highlowtech.org/?p=1695

Two parts of the case slide and snap into each other. Very sturdy, and no hinges are needed. The STL files for the casing are attached below.

Now finally the time to put everything together. All components connected to the circuit board are either mounted or enclosed by the 3D printed case. The volume knob and three audio connectors are mounted, and the battery, the circuit board, and the Bluetooth module will be placed in inside compartments like the picture above.

Now it's time to play! Here are some more samples. To use the effector, plug in the effector to your electric guitar and a pair of headphones to the 1/4" jack, and start playing. I built a simple openframeworks app that sends numbers to the effector so I can switch between presets. It simply makes a serial connection with the effector and sends a single integer.