mirror of
https://github.com/scrapcomputing/WavetablePi.git
synced 2026-10-26 21:50:15 +00:00
Adds a low-pass filter for PWM audio
Improves the audio quality of PWM audio with a simple low-pass filter. This uses R3-C3 and R4-C4 (one filter for each channel).
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/kicad/*-cache
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/kicad/*-cache.lib
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/kicad/*-bak
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/kicad/gerbers/*
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@@ -16,6 +16,7 @@ For controlling the mt32-pi from DOS, please use [mt32-pi-control](https://githu
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- It currently supports two modes of audio: using the raspberry pi's PWM audio out (which is noisy and sounds pretty bad), and an external Hi-Fi PCM5102A based DAC.
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- You can also attach a 0.91 OLED SSD1306 I2C 128x32 display.
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- Starting from rev 0.3 PWM audio is filtered by a simple low-pass filter (R3-C3 and R4-C4).
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# I want to build one myself!
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- Please note that the current version of the WavetablePi board is quite tall (76mm x 40mm) so please check if it fits your sound card, especially if it needs to be placed perpendicularly to the ISA slots.
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@@ -26,16 +27,18 @@ For controlling the mt32-pi from DOS, please use [mt32-pi-control](https://githu
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# Bill of materials
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Item | ## | Description
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Item | # | Description
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-----------------------------------------|-----|-----------------------------------------
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Raspberry Pi Zero 2 W | 1 | The older RPi Zero is not fast enough
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40-pin 2x20 male header 2.54mm pitch | 1 | For attaching the RPi to the board.
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26-pin 2x13 female header 2.54mm pitch | 1 | For attaching the board to the wavetable header
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6-pin 2x3 pin male header 2.54mm pitch | 1 | For the audio select jumpers
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Jumper 2.54mm pitch | 2 | Jumpers for the audio selection header
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10uF through-hole ceramic capacitors | 2 |
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Capacitor 10uF through-hole ceramic | 2 |
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Capacitor 100nF through-hole ceramic | 2 | C3 and C4 which form the PWM audio low-pass filter along with R3 and R4. 100nF is for a 1.6KHz cutoff frequency. Use lower values for higher cutoff
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Resistor 22K Ohm | 1 |
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Resistor 10K Ohm | 1 |
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Resistor 1K Ohm | 2 | R3 and R4, which along with C3 and C4 form a low-pass filter of the PWM audio
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0.91 OLED SSD1306 I2C 128x32 module | 1 | (Optional)
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PCM5102A I2S DAC Module | 1 | (Optional but highly recommended) Please check the PCB for the supported dimensions and form factor!
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@@ -308,8 +308,6 @@ Wire Wire Line
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1200 5800 3700 5800
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Wire Wire Line
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3600 5600 3600 5900
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Wire Wire Line
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3600 5900 4200 5900
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$Comp
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L power:GND #PWR0101
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U 1 1 61CC6CE4
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@@ -338,8 +336,6 @@ Wire Wire Line
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3000 4000 3000 3950
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Wire Wire Line
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3100 3950 3500 3950
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Wire Wire Line
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3500 3950 3500 4600
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Wire Wire Line
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4200 3450 3100 3450
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Wire Wire Line
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@@ -575,4 +571,89 @@ Wire Wire Line
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4300 6350 4400 6350
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Wire Wire Line
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4300 6250 4400 6250
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$Comp
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L Device:R R3
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U 1 1 63CD298C
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P 3500 4400
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F 0 "R3" H 3570 4446 50 0000 L CNN
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F 1 "1K" H 3570 4355 50 0000 L CNN
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F 2 "Resistor_THT:R_Axial_DIN0207_L6.3mm_D2.5mm_P7.62mm_Horizontal" V 3430 4400 50 0001 C CNN
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F 3 "~" H 3500 4400 50 0001 C CNN
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1 3500 4400
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1 0 0 -1
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$EndComp
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Wire Wire Line
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3500 4550 3500 4600
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$Comp
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L Device:C C3
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U 1 1 63CE57FB
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P 3350 4250
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F 0 "C3" V 3098 4250 50 0000 C CNN
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F 1 "100nF" V 3189 4250 50 0000 C CNN
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F 2 "Capacitor_THT:C_Rect_L7.0mm_W2.0mm_P5.00mm" H 3388 4100 50 0001 C CNN
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F 3 "~" H 3350 4250 50 0001 C CNN
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1 3350 4250
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0 1 1 0
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$EndComp
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$Comp
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L power:GND #PWR01
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U 1 1 63CE7538
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P 3200 4250
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F 0 "#PWR01" H 3200 4000 50 0001 C CNN
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F 1 "GND" H 3205 4077 50 0000 C CNN
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F 2 "" H 3200 4250 50 0001 C CNN
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F 3 "" H 3200 4250 50 0001 C CNN
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1 3200 4250
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1 0 0 -1
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$EndComp
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Wire Wire Line
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3500 3950 3500 4250
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Connection ~ 3500 4250
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$Comp
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L Device:R R4
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U 1 1 63CEAFF8
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P 3750 5900
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F 0 "R4" V 3543 5900 50 0000 C CNN
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F 1 "1K" V 3634 5900 50 0000 C CNN
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F 2 "Resistor_THT:R_Axial_DIN0207_L6.3mm_D2.5mm_P7.62mm_Horizontal" V 3680 5900 50 0001 C CNN
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F 3 "~" H 3750 5900 50 0001 C CNN
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1 3750 5900
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0 1 1 0
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$EndComp
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$Comp
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L Device:C C4
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U 1 1 63CEBC9D
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P 3900 6050
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F 0 "C4" H 4015 6096 50 0000 L CNN
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F 1 "C" H 4015 6005 50 0000 L CNN
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F 2 "Capacitor_THT:C_Rect_L7.0mm_W2.0mm_P5.00mm" H 3938 5900 50 0001 C CNN
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F 3 "~" H 3900 6050 50 0001 C CNN
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1 3900 6050
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1 0 0 -1
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$EndComp
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$Comp
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L power:GND #PWR02
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U 1 1 63CECB7F
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P 3900 6200
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F 0 "#PWR02" H 3900 5950 50 0001 C CNN
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F 1 "GND" H 3905 6027 50 0000 C CNN
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F 2 "" H 3900 6200 50 0001 C CNN
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F 3 "" H 3900 6200 50 0001 C CNN
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1 3900 6200
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1 0 0 -1
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$EndComp
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Wire Wire Line
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3900 5900 4200 5900
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Connection ~ 3900 5900
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$Comp
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L power:GND #PWR0121
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U 1 1 63D51184
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P 3350 2100
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F 0 "#PWR0121" H 3350 1850 50 0001 C CNN
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F 1 "GND" H 3355 1927 50 0000 C CNN
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F 2 "" H 3350 2100 50 0001 C CNN
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F 3 "" H 3350 2100 50 0001 C CNN
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1 3350 2100
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-1 0 0 1
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$EndComp
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$EndSCHEMATC
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