jblang/ATtiny84A_spectrum2ATtiny Spectrum Analyzer
Spectrum is an open-source printed circuit board by jblang, from the jblang/ATtiny84A_spectrum repository on GitHub. It is a 2-layer board of 55.2 × 40.6 mm with 24 parts on 22 nets, routed with 76 tracks and 0 vias.
It is built around the ATTINY84A-PU. Its parts include 9 resistors, 8 diodes, 3 connectors, 1 capacitor and 1 IC. It belongs with the sensors and measurement boards and the AVR (ATmega, ATtiny) boards of this library.
This is an 8-channel spectrum analyzer using ATtiny84A and an electret microphone. The 20x gain stage of the differential ADC is used so a separate amplifier is not necessary.
The code uses a DFT algorithm by Łukasz Podkalicki. Original code was based on his blog post, but after I contacted him he kindly shared a newer version of the code which I don't believe he had published previously. I adapted the newest code to the ATtiny84A with 8 channels and tweaked the thresholds to work with an electret microphone.
The code for an earlier experiment with the ATtiny13A is also included. The 13A doesn't include a gain stage on it's ADC so a LM386 audio amplifier was used to amplify the audio signal before passing it into the 13's ADC.
I have also designed a PCB for the ATtiny84A version but I haven't had it manufactured yet.
| Qty | Value | Footprint | References |
|---|---|---|---|
| 8 | 220R | Resistor_THT:R_Axial_DIN0207_L6.3mm_D2.5mm_P7.62mm_Horizontal | R4, R5, R6, R7, R8, R9, R10, R11 |
| 2 | BLUE | LED_THT:LED_D3.0mm | D1, D2 |
| 2 | GREEN | LED_THT:LED_D3.0mm | D3, D4 |
| 2 | RED | LED_THT:LED_D3.0mm | D7, D8 |
| 2 | YELLOW | LED_THT:LED_D3.0mm | D5, D6 |
| 1 | 10K | Resistor_THT:R_Axial_DIN0207_L6.3mm_D2.5mm_P7.62mm_Horizontal | R3 |
| 1 | 15K | Potentiometer_THT:Potentiometer_Bourns_3296P_Horizontal | RV1 |
| 1 | ATtiny84A-PU | Package_DIP:DIP-14_W7.62mm | U1 |
| 1 | C | Capacitor_THT:C_Disc_D3.0mm_W1.6mm_P2.50mm | C1 |
| 1 | ISP | Connector_PinHeader_2.54mm:PinHeader_2x03_P2.54mm_Horizontal | J3 |
| 1 | Microphone | Connector_PinHeader_2.54mm:PinHeader_1x02_P2.54mm_Vertical | MK1 |
| 1 | PWR | Connector_PinHeader_2.54mm:PinHeader_1x02_P2.54mm_Horizontal | J1 |
| 1 | TXD | Connector_PinHeader_2.54mm:PinHeader_1x02_P2.54mm_Horizontal | J2 |
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It measures 55.2 × 40.6 mm and has 2 copper layers, 1.6 mm thick.
24 parts, built around the ATTINY84A-PU. The full list of its parts is on this page, with links to each part's symbol and footprint where PCBKit's library has them.
From the jblang/ATtiny84A_spectrum repository on GitHub, at the commit this page was made from: the board is pcb/spectrum.kicad_pcb. PCBKit opens the board in the browser, with nothing to install.
Its repository states no licence, so its author keeps all rights: ask jblang before reusing the design.
