837 Acoustic Interferometer
837 : Acoustic Interferometer
- Author: Josef Gajdusek
- Description: Displays direction of arrival of an 20kHz tone on a LED bar
- GitHub repository
- Open in 3D viewer
- Open in Tiny Tapeout Explorer
- Clock: 10240000 Hz
How it works
- The two PDM microphones are sampled at 2.56MHz (4x slower than the design), producing a pair of 1-bit real signals
- These 1-bit real signals are then mixed with a 20kHz (2.560 / 128) complex tone at 6-bits, shifting the 20Khz carrier into DC
- These complex samples are then averaged over 2^16 samples as a low pass filter stage
- CORDIC in vectoring mode then computes the phase difference of the two samples, yielding a 7-bit signed integer
- This integer is then displayed as an one-hot value on an 16-LED bar
The phase angle computed in step 4. is also transmitted over UART for debugging purposes.
How to test
Connect the designated PMOD PCB. Then, play a 20kHz tone using a phone speaker (preferably only either left or right speaker). The green LED bar should track the direction of arrival. The UART should transmit single bytes containing the relative angle computed each integration period.
External hardware
Built for a PMOD PCB available at the source repo. It could also possibly be jury rigged from LMD3526B261 modules and a bunch of LEDs on a breadboard.
IO
| # | Input | Output | Bidirectional |
|---|---|---|---|
| 0 | MIC_LEFT | PDM_CLK | LED_0 |
| 1 | MIC_RIGHT | LED_POS | LED_1 |
| 2 | LED_NEG | LED_2 | |
| 3 | PHASE_UART | LED_3 | |
| 4 | LED_4 | ||
| 5 | LED_5 | ||
| 6 | LED_6 | ||
| 7 | LED_7 |