ATtiny412 Voice Changer

# Overview The ATtiny412 VoiceChanger is a simple device for changing the pitch of speech and other audio signals. An electret microphone is installed for audio input, and a small loudspeaker can be connected directly to the board for output. * Firmware (EasyEDA): [https://github.com/wagiminator/ATtiny412-VoiceChanger](https://github.com/wagiminator/ATtiny412-VoiceChanger)  # Hardware The schematic is shown below:  The inexpensive LMV358 rail-to-rail dual OpAmp is used to amplify the audio signals. The first OpAmp amplifies the weak signal from the electret microphone. The amplification factor is determined by resistors R2 and R3 (Gain = R3 / R2 = 47). If desired, the gain can be increased by replacing the 47k (R3) with a 100k resistor, which will also increase the output volume. The voltage divider formed by R4 and R5 at the positive input of the OpAmp defines the virtual ground and lets the audio signal oscillate around half the supply voltage. The output of the first OpAmp is connected to the ATtiny's analog-to-digital converter (ADC), which samples the amplified audio signal. This signal is modified by the ATtiny and output via its digital-to-analog converter (DAC). Since the DAC cannot drive a load directly, the signal is amplified by the LMV358's second OpAmp, which is configured as a voltage follower/buffer. The output of this OpAmp drives the speaker through a coupling capacitor (C2).  # Software ## Implementation The amplified input signal is sampled by the ATtiny's ADC. For this purpose, the ADC is operated in free-running mode with a resolution of 8 bits and an ADC clock frequency of 500kHz. This results in a sampling rate of 500kHz/13 = 38kHz. After each conversion, an interrupt is triggered, in the service routine of which the sampled value is pushed into a 192-byte ring buffer. ``` c // =================================================================================== // Ring Buffer Implementation // =================================================================================== #define BUF_LEN 192 // buffer length volatile uint8_t BUF_buffer[BUF_LEN];           // this is the buffer volatile uint8_t BUF_head, BUF_tail;            // head and tail pointer // Push byte to ring buffer void BUF_push(uint8_t data) { if(++BUF_head >= BUF_LEN) BUF_head = 0; // increase head pointer BUF_buffer[BUF_head] = data; // push data byte to buffer } // Pop data byte from buffer uint8_t BUF_pop(void) { if(++BUF_tail >= BUF_LEN) BUF_tail = 0; // increase tail pointer return BUF_buffer[BUF_tail]; // pop data byte from buffer } // =================================================================================== // ADC Implementation for Audio Input // =================================================================================== // Init analog to digital converter (ADC) void ADC_init(void) { pinDisable(PIN_ADC); // disable digital input buffer ADC0.CTRLA = ADC_RESSEL_8BIT_gc // 8-bit resolution | ADC_FREERUN_bm // free running mode | ADC_ENABLE_bm; // enable ADC ADC0.CTRLC = ADC_SAMPCAP_bm // select sample capacitance | ADC_REFSEL_VDDREF_gc // set Vdd as reference | ADC_PRESC_DIV8_gc; // set prescaler -> 500kHz ADC clock ADC0.MUXPOS = PIN_ADC; // set the input pin ADC0.INTCTRL = ADC_RESRDY_bm; // enable result ready interrupt ADC0.COMMAND = ADC_STCONV_bm; // start first conversion } // ADC result ready interrupt service routine ISR(ADC0_RESRDY_vect) { BUF_push(ADC0.RESL); // push result to buffer } ``` The timer/counter B (TCB) is set up in such a way that it periodically triggers another interrupt, in the service routine of which a value is pulled from the ring buffer and written to the data register of the DAC. The frequency of these interrupts can be changed using the keys. If the frequency of the timer interrupts is equal to the ADC sampling frequency (38kHz), the output signal also corresponds to the input signal. If the frequency of the timer interrupt is higher than the sampling frequency of the ADC, the pitch of the audio signal will be increased and vice versa. ``` c // =================================================================================== // DAC Implementation for Audio Output // =================================================================================== // Setup the digital to analog converter (DAC) void DAC_init(void) { pinDisable(PIN_DAC); // disable digital input buffer VREF_CTRLA |= VREF_DAC0REFSEL_4V34_gc; // set DAC reference to 4.3V DAC0.CTRLA = DAC_ENABLE_bm // enable DAC | DAC_OUTEN_bm; // enable output buffer } // Set DAC value void DAC_set(uint8_t value) { DAC0.DATA = value; // set DAC } // =================================================================================== // Periodic Interrupt Implementation using TCB for Audio Output // =================================================================================== // Init timer/counter B (TCB) void TCB_init(void) { TCB0.CTRLA = TCB_CLKSEL_CLKDIV1_gc // set prescaler | TCB_ENABLE_bm; // enable timer TCB0.CTRLB = TCB_CNTMODE_INT_gc; // set timer to periodic interrupt mode TCB0.CCMP = PITCH_START; // set TOP value TCB0.INTCTRL = TCB_CAPT_bm; // enable interrupt } // Set pitch value void TCB_setPitch(uint8_t value) { TCB0.CCMP = value; // set pitch value TCB0.CNT = 0; // reset counter } // Timer interrupt service routine ISR(TCB0_INT_vect) { TCB0.INTFLAGS = TCB_CAPT_bm; // clear interrupt flag DAC_set(BUF_pop()); // set DAC value from buffer } ``` ## Compiling and Uploading the Firmware ### If using the Arduino IDE * Open your Arduino IDE. * Make sure you have installed [megaTinyCore](https://github.com/SpenceKonde/megaTinyCore). * Go to **Tools -> Board -> megaTinyCore** and select **ATtiny412/402/212/202**. * Go to **Tools** and choose the following board options: * **Chip:** ATtiny412 * **Clock:** 4 MHz internal * Leave the rest at the default settings. * Connect your programmer to your PC and to the UPDI header on the board. * Go to **Tools -> Programmer** and select your UPDI programmer. * Go to **Tools -> Burn Bootloader** to burn the fuses. * Open the sketch and click **Upload**. ### If using the makefile (Linux/Mac) * Connect your [programmer](https://github.com/wagiminator/AVR-Programmer) (jtag2updi or SerialUPDI) to your PC and to the UPDI header on the board. * Download [AVR 8-bit Toolchain](https://www.microchip.com/mplab/avr-support/avr-and-arm-toolchains-c-compilers) and extract the sub-folders (avr, bin, include, ...) to /software/tools/avr-gcc. To do this, you have to register for free with Microchip on the download site. * Open the makefile and set the programmer and port (default is serialupdi on /dev/ttyUSB0). * Open a terminal. * Navigate to the folder with the makefile and the sketch. * Run `make install` to compile, burn the fuses and upload the firmware. # Operating Instructions 1. Connect a 5V power supply to the respective header on the board. Pay attention to the correct polarity! 2. Connect a little speaker (max 3W/4Ω) to the respective header. 3. Turn on the switch and speak into the microphone. 4. Use the buttons to modify the pitch. # References, Links and Notes 1. [ATtiny412 Datasheet](https://ww1.microchip.com/downloads/aemDocuments/documents/MCU08/ProductDocuments/DataSheets/ATtiny212-214-412-414-416-DataSheet-DS40002287A.pdf) 2. [LMV358 Datasheet](https://datasheet.lcsc.com/szlcsc/Texas-Instruments-TI-LMV358IDR_C63813.pdf) # License  This work is licensed under Creative Commons Attribution-ShareAlike 3.0 Unported License. (http://creativecommons.org/licenses/by-sa/3.0/)