Add polyphony, update readme

Author: Jan Knipper

README.md

@@ -1,26 +1,26 @@
-# Raspberry Pi Pico DCO
+# Raspberry Pi Pico Polyphonic DCO
 
-This repository contains source code and schematics for a digitally controlled oscillator (DCO) which is driven by a Raspberry Pi Pico. It uses PIO to generate a highly accurate frequency which is controlled by MIDI USB. The analog oscillator part is based on the Juno 106 and generates sawtooth and square wave signal with a 10Vpp amplitude. Amplitude compensation is done by a smoothed PWM signal coming from the Pico.
+This repository contains source code, schematics and PCB for a digitally controlled oscillator (DCO) with up to 6 voices which are driven by a Raspberry Pi Pico. It uses PIO to generate a highly accurate frequency which is controlled by USB or serial MIDI. The analog oscillator part is based on the Juno 106 and generates sawtooth and square wave signal with a 10Vpp amplitude. Amplitude compensation is done by a smoothed PWM signal coming from the Pico.
 
-This is how it sounds: [Ramp sample](https://soundcloud.com/polykit/pico-dco-ramp) [Pulse sample](https://soundcloud.com/polykit/pico-dco-pulse)
+This is how it sounds: [Ramp sample](https://soundcloud.com/polykit/pico-dco-ramp) [Pulse sample](https://soundcloud.com/polykit/pico-dco-pulse) [Polyphonic sample](https://soundcloud.com/polykit/pico-dco-polyphonic)
 
-## Schematics
+## Schematics and PCB
 
 ![Raspberry Pi Pico DCO](pico-dco.png)
 
+![Raspberry Pi Pico DCO PCB](pico-dco-pcb.png)
+
 ## Installing (simple)
 
 Press `BOOTSEL` button on the Pico while powering it with USB. Copy file `build/pico-dco.uf2` onto the USB mass storage device.
 
 ## Usage
 
-After installing the Pico should register as USB MIDI device. The DCO listens to note on/note off messages on MIDI channel 1.
+After installing the Pico should register as USB MIDI device. Alternatively serial MIDI input is available. The DCO listens to note on/note off messages on MIDI channel 1.
 
-## Todo
+## Known issues
 
-- Add DIN MIDI input
-- Add polyphony (up to 8 voices should be possible)
-- Add velocity and pitch bend output (additional DAC needed)
+- USB MIDI apparently looses notes while playing. This seems to be caused by the TinyUSB library included in the Raspberry Pi Pico SDK. Hopefully this will be fixed in a future release.
 
 ## References
 

build/pico-dco.uf2

@@ -36,7 +36,7 @@ AR Path="/60ADE329/60873A52" Ref="R34"  Part="1"
 AR Path="/60ADFCBC/60873A52" Ref="R48"  Part="1" 
 AR Path="/60AE15A4/60873A52" Ref="R62"  Part="1" 
 AR Path="/60AE2DA8/60873A52" Ref="R76"  Part="1" 
-F 0 "R20" V 3693 2850 50  0000 C CNN
+F 0 "R76" V 3693 2850 50  0000 C CNN
 F 1 "100k" V 3784 2850 50  0000 C CNN
 F 2 "Resistor_THT:R_Axial_DIN0207_L6.3mm_D2.5mm_P10.16mm_Horizontal" V 3830 2850 50  0001 C CNN
 F 3 "~" H 3900 2850 50  0001 C CNN
@@ -58,7 +58,7 @@ AR Path="/60ADE329/60873A58" Ref="R33"  Part="1"
 AR Path="/60ADFCBC/60873A58" Ref="R47"  Part="1" 
 AR Path="/60AE15A4/60873A58" Ref="R61"  Part="1" 
 AR Path="/60AE2DA8/60873A58" Ref="R75"  Part="1" 
-F 0 "R19" V 2893 3100 50  0000 C CNN
+F 0 "R75" V 2893 3100 50  0000 C CNN
 F 1 "100k" V 2984 3100 50  0000 C CNN
 F 2 "Resistor_THT:R_Axial_DIN0207_L6.3mm_D2.5mm_P10.16mm_Horizontal" V 3030 3100 50  0001 C CNN
 F 3 "~" H 3100 3100 50  0001 C CNN
@@ -128,7 +128,7 @@ AR Path="/60ADE329/60873A7B" Ref="R43"  Part="1"
 AR Path="/60ADFCBC/60873A7B" Ref="R57"  Part="1" 
 AR Path="/60AE15A4/60873A7B" Ref="R71"  Part="1" 
 AR Path="/60AE2DA8/60873A7B" Ref="R85"  Part="1" 
-F 0 "R29" H 6280 4204 50  0000 R CNN
+F 0 "R85" H 6280 4204 50  0000 R CNN
 F 1 "100k" H 6280 4295 50  0000 R CNN
 F 2 "Resistor_THT:R_Axial_DIN0207_L6.3mm_D2.5mm_P10.16mm_Horizontal" V 6280 4250 50  0001 C CNN
 F 3 "~" H 6350 4250 50  0001 C CNN
@@ -150,7 +150,7 @@ AR Path="/60ADE329/60873A81" Ref="C19"  Part="1"
 AR Path="/60ADFCBC/60873A81" Ref="C24"  Part="1" 
 AR Path="/60AE15A4/60873A81" Ref="C29"  Part="1" 
 AR Path="/60AE2DA8/60873A81" Ref="C34"  Part="1" 
-F 0 "C14" V 6355 3750 50  0000 C CNN
+F 0 "C34" V 6355 3750 50  0000 C CNN
 F 1 "10u" V 6264 3750 50  0000 C CNN
 F 2 "Capacitor_THT:CP_Radial_D5.0mm_P2.00mm" H 6138 3600 50  0001 C CNN
 F 3 "~" H 6100 3750 50  0001 C CNN
@@ -177,7 +177,7 @@ AR Path="/60ADE329/60873A8A" Ref="U5"  Part="2"
 AR Path="/60ADFCBC/60873A8A" Ref="U6"  Part="2" 
 AR Path="/60AE15A4/60873A8A" Ref="U7"  Part="2" 
 AR Path="/60AE2DA8/60873A8A" Ref="U8"  Part="2" 
-F 0 "U4" H 3900 3567 50  0000 C CNN
+F 0 "U8" H 3900 3567 50  0000 C CNN
 F 1 "TL074" H 3900 3476 50  0000 C CNN
 F 2 "Package_DIP:DIP-14_W7.62mm_Socket_LongPads" H 3850 3300 50  0001 C CNN
 F 3 "http://www.ti.com/lit/ds/symlink/tl071.pdf" H 3950 3400 50  0001 C CNN
@@ -228,7 +228,7 @@ AR Path="/60ADE329/60873A9A" Ref="R36"  Part="1"
 AR Path="/60ADFCBC/60873A9A" Ref="R50"  Part="1" 
 AR Path="/60AE15A4/60873A9A" Ref="R64"  Part="1" 
 AR Path="/60AE2DA8/60873A9A" Ref="R78"  Part="1" 
-F 0 "R22" V 4343 3200 50  0000 C CNN
+F 0 "R78" V 4343 3200 50  0000 C CNN
 F 1 "100k" V 4434 3200 50  0000 C CNN
 F 2 "Resistor_THT:R_Axial_DIN0207_L6.3mm_D2.5mm_P10.16mm_Horizontal" V 4480 3200 50  0001 C CNN
 F 3 "~" H 4550 3200 50  0001 C CNN
@@ -254,7 +254,7 @@ AR Path="/60ADE329/60873AA2" Ref="U5"  Part="1"
 AR Path="/60ADFCBC/60873AA2" Ref="U6"  Part="1" 
 AR Path="/60AE15A4/60873AA2" Ref="U7"  Part="1" 
 AR Path="/60AE2DA8/60873AA2" Ref="U8"  Part="1" 
-F 0 "U4" H 5300 3667 50  0000 C CNN
+F 0 "U8" H 5300 3667 50  0000 C CNN
 F 1 "TL074" H 5300 3576 50  0000 C CNN
 F 2 "Package_DIP:DIP-14_W7.62mm_Socket_LongPads" H 5250 3400 50  0001 C CNN
 F 3 "http://www.ti.com/lit/ds/symlink/tl071.pdf" H 5350 3500 50  0001 C CNN
@@ -321,7 +321,7 @@ AR Path="/60ADE329/60873ABA" Ref="C17"  Part="1"
 AR Path="/60ADFCBC/60873ABA" Ref="C22"  Part="1" 
 AR Path="/60AE15A4/60873ABA" Ref="C27"  Part="1" 
 AR Path="/60AE2DA8/60873ABA" Ref="C32"  Part="1" 
-F 0 "C12" V 3848 1550 50  0000 C CNN
+F 0 "C32" V 3848 1550 50  0000 C CNN
 F 1 "470p" V 3939 1550 50  0000 C CNN
 F 2 "Capacitor_THT:C_Rect_L7.2mm_W4.5mm_P5.00mm_FKS2_FKP2_MKS2_MKP2" H 4138 1400 50  0001 C CNN
 F 3 "~" H 4100 1550 50  0001 C CNN
@@ -343,7 +343,7 @@ AR Path="/60ADE329/60873AC0" Ref="R35"  Part="1"
 AR Path="/60ADFCBC/60873AC0" Ref="R49"  Part="1" 
 AR Path="/60AE15A4/60873AC0" Ref="R63"  Part="1" 
 AR Path="/60AE2DA8/60873AC0" Ref="R77"  Part="1" 
-F 0 "R21" H 4520 1846 50  0000 L CNN
+F 0 "R77" H 4520 1846 50  0000 L CNN
 F 1 "10k" H 4520 1755 50  0000 L CNN
 F 2 "Resistor_THT:R_Axial_DIN0207_L6.3mm_D2.5mm_P10.16mm_Horizontal" V 4380 1800 50  0001 C CNN
 F 3 "~" H 4450 1800 50  0001 C CNN
@@ -365,7 +365,7 @@ AR Path="/60ADE329/60873AC6" Ref="R37"  Part="1"
 AR Path="/60ADFCBC/60873AC6" Ref="R51"  Part="1" 
 AR Path="/60AE15A4/60873AC6" Ref="R65"  Part="1" 
 AR Path="/60AE2DA8/60873AC6" Ref="R79"  Part="1" 
-F 0 "R23" V 4593 1550 50  0000 C CNN
+F 0 "R79" V 4593 1550 50  0000 C CNN
 F 1 "1k" V 4684 1550 50  0000 C CNN
 F 2 "Resistor_THT:R_Axial_DIN0207_L6.3mm_D2.5mm_P10.16mm_Horizontal" V 4730 1550 50  0001 C CNN
 F 3 "~" H 4800 1550 50  0001 C CNN
@@ -387,7 +387,7 @@ AR Path="/60ADE329/60873ACC" Ref="R41"  Part="1"
 AR Path="/60ADFCBC/60873ACC" Ref="R55"  Part="1" 
 AR Path="/60AE15A4/60873ACC" Ref="R69"  Part="1" 
 AR Path="/60AE2DA8/60873ACC" Ref="R83"  Part="1" 
-F 0 "R27" H 5720 2396 50  0000 L CNN
+F 0 "R83" H 5720 2396 50  0000 L CNN
 F 1 "2k2" H 5720 2305 50  0000 L CNN
 F 2 "Resistor_THT:R_Axial_DIN0207_L6.3mm_D2.5mm_P10.16mm_Horizontal" V 5580 2350 50  0001 C CNN
 F 3 "~" H 5650 2350 50  0001 C CNN
@@ -409,7 +409,7 @@ AR Path="/60ADE329/60873AD2" Ref="C18"  Part="1"
 AR Path="/60ADFCBC/60873AD2" Ref="C23"  Part="1" 
 AR Path="/60AE15A4/60873AD2" Ref="C28"  Part="1" 
 AR Path="/60AE2DA8/60873AD2" Ref="C33"  Part="1" 
-F 0 "C13" V 5048 2700 50  0000 C CNN
+F 0 "C33" V 5048 2700 50  0000 C CNN
 F 1 "1n*" V 5139 2700 50  0000 C CNN
 F 2 "Capacitor_THT:C_Rect_L7.2mm_W4.5mm_P5.00mm_FKS2_FKP2_MKS2_MKP2" H 5338 2550 50  0001 C CNN
 F 3 "~" H 5300 2700 50  0001 C CNN
@@ -431,7 +431,7 @@ AR Path="/60ADE329/60873AD8" Ref="Q3"  Part="1"
 AR Path="/60ADFCBC/60873AD8" Ref="Q4"  Part="1" 
 AR Path="/60AE15A4/60873AD8" Ref="Q5"  Part="1" 
 AR Path="/60AE2DA8/60873AD8" Ref="Q6"  Part="1" 
-F 0 "Q2" V 5535 1900 50  0000 C CNN
+F 0 "Q6" V 5535 1900 50  0000 C CNN
 F 1 "2N3904" V 5626 1900 50  0000 C CNN
 F 2 "Package_TO_SOT_THT:TO-92_Wide" H 5500 1825 50  0001 L CIN
 F 3 "https://www.onsemi.com/pub/Collateral/2N3903-D.PDF" H 5300 1900 50  0001 L CNN
@@ -453,7 +453,7 @@ AR Path="/60ADE329/60873ADE" Ref="U5"  Part="4"
 AR Path="/60ADFCBC/60873ADE" Ref="U6"  Part="4" 
 AR Path="/60AE15A4/60873ADE" Ref="U7"  Part="4" 
 AR Path="/60AE2DA8/60873ADE" Ref="U8"  Part="4" 
-F 0 "U4" H 6200 5867 50  0000 C CNN
+F 0 "U8" H 6200 5867 50  0000 C CNN
 F 1 "TL074" H 6200 5776 50  0000 C CNN
 F 2 "Package_DIP:DIP-14_W7.62mm_Socket_LongPads" H 6150 5600 50  0001 C CNN
 F 3 "http://www.ti.com/lit/ds/symlink/tl071.pdf" H 6250 5700 50  0001 C CNN
@@ -477,7 +477,7 @@ AR Path="/60ADE329/60873AE5" Ref="R42"  Part="1"
 AR Path="/60ADFCBC/60873AE5" Ref="R56"  Part="1" 
 AR Path="/60AE15A4/60873AE5" Ref="R70"  Part="1" 
 AR Path="/60AE2DA8/60873AE5" Ref="R84"  Part="1" 
-F 0 "R28" H 5580 4204 50  0000 R CNN
+F 0 "R84" H 5580 4204 50  0000 R CNN
 F 1 "10k" H 5580 4295 50  0000 R CNN
 F 2 "Resistor_THT:R_Axial_DIN0207_L6.3mm_D2.5mm_P10.16mm_Horizontal" V 5580 4250 50  0001 C CNN
 F 3 "~" H 5650 4250 50  0001 C CNN
@@ -499,7 +499,7 @@ AR Path="/60ADE329/60873AF2" Ref="R40"  Part="1"
 AR Path="/60ADFCBC/60873AF2" Ref="R54"  Part="1" 
 AR Path="/60AE15A4/60873AF2" Ref="R68"  Part="1" 
 AR Path="/60AE2DA8/60873AF2" Ref="R82"  Part="1" 
-F 0 "R26" H 5370 5996 50  0000 L CNN
+F 0 "R82" H 5370 5996 50  0000 L CNN
 F 1 "470k" H 5370 5905 50  0000 L CNN
 F 2 "Resistor_THT:R_Axial_DIN0207_L6.3mm_D2.5mm_P10.16mm_Horizontal" V 5230 5950 50  0001 C CNN
 F 3 "~" H 5300 5950 50  0001 C CNN
@@ -521,7 +521,7 @@ AR Path="/60ADE329/60873AF8" Ref="R38"  Part="1"
 AR Path="/60ADFCBC/60873AF8" Ref="R52"  Part="1" 
 AR Path="/60AE15A4/60873AF8" Ref="R66"  Part="1" 
 AR Path="/60AE2DA8/60873AF8" Ref="R80"  Part="1" 
-F 0 "R24" V 5007 4650 50  0000 C CNN
+F 0 "R80" V 5007 4650 50  0000 C CNN
 F 1 "150k" V 4916 4650 50  0000 C CNN
 F 2 "Resistor_THT:R_Axial_DIN0207_L6.3mm_D2.5mm_P10.16mm_Horizontal" V 4730 4650 50  0001 C CNN
 F 3 "~" H 4800 4650 50  0001 C CNN
@@ -543,7 +543,7 @@ AR Path="/60ADE329/60873AFE" Ref="R39"  Part="1"
 AR Path="/60ADFCBC/60873AFE" Ref="R53"  Part="1" 
 AR Path="/60AE15A4/60873AFE" Ref="R67"  Part="1" 
 AR Path="/60AE2DA8/60873AFE" Ref="R81"  Part="1" 
-F 0 "R25" V 5007 5600 50  0000 C CNN
+F 0 "R81" V 5007 5600 50  0000 C CNN
 F 1 "100k" V 4916 5600 50  0000 C CNN
 F 2 "Resistor_THT:R_Axial_DIN0207_L6.3mm_D2.5mm_P10.16mm_Horizontal" V 4730 5600 50  0001 C CNN
 F 3 "~" H 4800 5600 50  0001 C CNN
@@ -597,7 +597,7 @@ AR Path="/60ADE329/60873B1E" Ref="R44"  Part="1"
 AR Path="/60ADFCBC/60873B1E" Ref="R58"  Part="1" 
 AR Path="/60AE15A4/60873B1E" Ref="R72"  Part="1" 
 AR Path="/60AE2DA8/60873B1E" Ref="R86"  Part="1" 
-F 0 "R30" V 6593 5500 50  0000 C CNN
+F 0 "R86" V 6593 5500 50  0000 C CNN
 F 1 "10k" V 6684 5500 50  0000 C CNN
 F 2 "Resistor_THT:R_Axial_DIN0207_L6.3mm_D2.5mm_P10.16mm_Horizontal" V 6730 5500 50  0001 C CNN
 F 3 "~" H 6800 5500 50  0001 C CNN
@@ -619,7 +619,7 @@ AR Path="/60ADE329/60873B24" Ref="R45"  Part="1"
 AR Path="/60ADFCBC/60873B24" Ref="R59"  Part="1" 
 AR Path="/60AE15A4/60873B24" Ref="R73"  Part="1" 
 AR Path="/60AE2DA8/60873B24" Ref="R87"  Part="1" 
-F 0 "R31" H 7120 5796 50  0000 L CNN
+F 0 "R87" H 7120 5796 50  0000 L CNN
 F 1 "5k6" H 7120 5705 50  0000 L CNN
 F 2 "Resistor_THT:R_Axial_DIN0207_L6.3mm_D2.5mm_P10.16mm_Horizontal" V 6980 5750 50  0001 C CNN
 F 3 "~" H 7050 5750 50  0001 C CNN
@@ -710,7 +710,7 @@ AR Path="/60ADE329/60873B5B" Ref="R32"  Part="1"
 AR Path="/60ADFCBC/60873B5B" Ref="R46"  Part="1" 
 AR Path="/60AE15A4/60873B5B" Ref="R60"  Part="1" 
 AR Path="/60AE2DA8/60873B5B" Ref="R74"  Part="1" 
-F 0 "R18" V 2293 3100 50  0000 C CNN
+F 0 "R74" V 2293 3100 50  0000 C CNN
 F 1 "4k7" V 2384 3100 50  0000 C CNN
 F 2 "Resistor_THT:R_Axial_DIN0207_L6.3mm_D2.5mm_P10.16mm_Horizontal" V 2430 3100 50  0001 C CNN
 F 3 "~" H 2500 3100 50  0001 C CNN
@@ -756,7 +756,7 @@ AR Path="/60ADE329/60873B69" Ref="C16"  Part="1"
 AR Path="/60ADFCBC/60873B69" Ref="C21"  Part="1" 
 AR Path="/60AE15A4/60873B69" Ref="C26"  Part="1" 
 AR Path="/60AE2DA8/60873B69" Ref="C31"  Part="1" 
-F 0 "C11" V 2548 3400 50  0000 C CNN
+F 0 "C31" V 2548 3400 50  0000 C CNN
 F 1 "100n" V 2639 3400 50  0000 C CNN
 F 2 "Capacitor_THT:C_Rect_L7.2mm_W4.5mm_P5.00mm_FKS2_FKP2_MKS2_MKP2" H 2838 3250 50  0001 C CNN
 F 3 "~" H 2800 3400 50  0001 C CNN
@@ -801,7 +801,7 @@ AR Path="/60ADE329/60873A65" Ref="U5"  Part="3"
 AR Path="/60ADFCBC/60873A65" Ref="U6"  Part="3" 
 AR Path="/60AE15A4/60873A65" Ref="U7"  Part="3" 
 AR Path="/60AE2DA8/60873A65" Ref="U8"  Part="3" 
-F 0 "U4" H 7350 4217 50  0000 C CNN
+F 0 "U8" H 7350 4217 50  0000 C CNN
 F 1 "TL074" H 7350 4126 50  0000 C CNN
 F 2 "Package_DIP:DIP-14_W7.62mm_Socket_LongPads" H 7300 3950 50  0001 C CNN
 F 3 "http://www.ti.com/lit/ds/symlink/tl071.pdf" H 7400 4050 50  0001 C CNN
@@ -822,7 +822,7 @@ AR Path="/60ADE329/60926AFD" Ref="U5"  Part="5"
 AR Path="/60ADFCBC/60926AFD" Ref="U6"  Part="5" 
 AR Path="/60AE15A4/60926AFD" Ref="U7"  Part="5" 
 AR Path="/60AE2DA8/60926AFD" Ref="U8"  Part="5" 
-F 0 "U4" H 9958 5596 50  0000 L CNN
+F 0 "U8" H 9958 5596 50  0000 L CNN
 F 1 "TL074" H 9958 5505 50  0000 L CNN
 F 2 "" H 9950 5650 50  0001 C CNN
 F 3 "http://www.ti.com/lit/ds/symlink/tl071.pdf" H 10050 5750 50  0001 C CNN
@@ -886,7 +886,7 @@ AR Path="/60ADE329/609307F0" Ref="C20"  Part="1"
 AR Path="/60ADFCBC/609307F0" Ref="C25"  Part="1" 
 AR Path="/60AE15A4/609307F0" Ref="C30"  Part="1" 
 AR Path="/60AE2DA8/609307F0" Ref="C35"  Part="1" 
-F 0 "C15" V 9398 5600 50  0000 C CNN
+F 0 "C35" V 9398 5600 50  0000 C CNN
 F 1 "100n" V 9489 5600 50  0000 C CNN
 F 2 "Capacitor_THT:C_Rect_L7.2mm_W4.5mm_P5.00mm_FKS2_FKP2_MKS2_MKP2" H 9688 5450 50  0001 C CNN
 F 3 "~" H 9650 5600 50  0001 C CNN

kicad/Pico-DCO-1.sch

@@ -1,4 +1,4 @@
-update=Mo 10 Mai 2021 23:23:45 CEST
+update=So 23 Mai 2021 22:49:11 CEST
 version=1
 last_client=kicad
 [general]
@@ -249,3 +249,13 @@ uViaDrill=0.1
 dPairWidth=0.2
 dPairGap=0.25
 dPairViaGap=0.25
+[schematic_editor]
+version=1
+PageLayoutDescrFile=
+PlotDirectoryName=../
+SubpartIdSeparator=0
+SubpartFirstId=65
+NetFmtName=
+SpiceAjustPassiveValues=0
+LabSize=50
+ERC_TestSimilarLabels=1

kicad/pico-dco.pro

@@ -814,10 +814,10 @@ F 3 "~" H 3750 3800 50  0001 C CNN
 	1    0    0    -1  
 $EndComp
 $Comp
-L Regulator_Linear:L7805 U?
+L Regulator_Linear:L7805 U1
 U 1 1 61096C61
 P 1900 6400
-F 0 "U?" H 1900 6642 50  0000 C CNN
+F 0 "U1" H 1900 6642 50  0000 C CNN
 F 1 "L7805" H 1900 6551 50  0000 C CNN
 F 2 "Package_TO_SOT_THT:TO-220-3_Vertical" H 1925 6250 50  0001 L CIN
 F 3 "http://www.st.com/content/ccc/resource/technical/document/datasheet/41/4f/b3/b0/12/d4/47/88/CD00000444.pdf/files/CD00000444.pdf/jcr:content/translations/en.CD00000444.pdf" H 1900 6350 50  0001 C CNN

kicad/pico-dco.sch

@@ -10,13 +10,15 @@
 #include "tusb.h"
 #include "hardware/uart.h"
 
-#define NUM_VOICES 1
+#define NUM_VOICES 6
 #define MIDI_CHANNEL 1
 
 const float BASE_NOTE = 440.0f;
-const uint8_t OUT_PINS[NUM_VOICES] = {2};
-const uint8_t RANGE_PINS[NUM_VOICES] = {3};
-const uint8_t GATE_PINS[NUM_VOICES] = {4};
+const uint8_t RESET_PINS[NUM_VOICES] = {13, 8, 12, 9, 11, 10};
+const uint8_t RANGE_PINS[NUM_VOICES] = {16, 19, 15, 18, 14, 17};
+const uint8_t GATE_PINS[NUM_VOICES] = {2, 3, 4, 5, 6, 7};
+const uint8_t VOICE_TO_PIO[NUM_VOICES] = {0, 0, 0, 0, 1, 1};
+const uint8_t VOICE_TO_SM[NUM_VOICES] = {0, 1, 2, 3, 0, 1};
 const uint16_t DIV_COUNTER = 1250;
 uint8_t RANGE_PWM_SLICES[NUM_VOICES];
 uint8_t NOTES[128];
@@ -58,9 +60,11 @@ int main() {
     }
 
     // pio init
+    uint offset[2];
+    offset[0] = pio_add_program(pio[0], &frequency_program);
+    offset[1] = pio_add_program(pio[1], &frequency_program);
     for (int i=0; i<NUM_VOICES; i++) {
-        uint offset = pio_add_program(pio[0], &frequency_program);
-        init_sm(pio[0], i, offset, OUT_PINS[i]);
+        init_sm(pio[VOICE_TO_PIO[i]], VOICE_TO_SM[i], offset[VOICE_TO_PIO[i]], RESET_PINS[i]);
     }
 
     // gate gpio init
@@ -84,7 +88,9 @@ void init_sm(PIO pio, uint sm, uint offset, uint pin) {
 }
 
 void set_frequency(PIO pio, uint sm, float freq) {
-    pio_sm_put(pio, sm, clock_get_hz(clk_sys) / 2 / freq);
+    uint32_t clk_div = clock_get_hz(clk_sys) / 2 / freq;
+    if (freq == 0) clk_div = 0;
+    pio_sm_put(pio, sm, clk_div);
     pio_sm_exec(pio, sm, pio_encode_pull(false, false));
     pio_sm_exec(pio, sm, pio_encode_out(pio_y, 32));
 }
@@ -148,10 +154,11 @@ void serial_midi_task() {
 }
 
 void note_on(uint8_t note, uint8_t velocity) {
+    if (NOTES[note] > 0) return; // note already playing
     uint8_t voice_num = get_free_voice();
     NOTES[note] = voice_num;
     float freq = get_freq_from_midi_note(note);
-    set_frequency(pio[0], voice_num, freq);
+    set_frequency(pio[VOICE_TO_PIO[voice_num]], VOICE_TO_SM[voice_num], freq);
     // amplitude adjustment
     pwm_set_chan_level(RANGE_PWM_SLICES[voice_num], pwm_gpio_to_channel(RANGE_PINS[voice_num]), (int)(DIV_COUNTER*(freq*0.00025f-1/(100*freq))));
     // gate on
@@ -162,12 +169,23 @@ void note_off(uint8_t note) {
     // gate off
     gpio_put(GATE_PINS[NOTES[note]], 0);
     VOICES[NOTES[note]] = 0;
+    NOTES[note] = 0;
 }
 
 uint8_t get_free_voice() {
-    uint8_t voice = 0;
-    VOICES[voice] = board_millis();
-    return voice;
+    uint32_t oldest_time = board_millis();
+    uint8_t oldest_voice = 0;
+    for (int i=0; i<NUM_VOICES; i++) {
+        if (VOICES[i] == 0) {
+            VOICES[i] = board_millis();
+            return i;
+        }
+        if (VOICES[i]<oldest_time) {
+            oldest_time = VOICES[i];
+            oldest_voice = i;
+        }
+    }
+    return oldest_voice;
 }
 
 void led_blinking_task(void) {