FPGA Based Theremin Project: : Cora Z7 Theremin Shield

This page describes design of theremin shield for Cora Z7

Connected to Cora Z7 board using Arduino/Chipkit connector.

Two on-board PMods of Cora board are left unused for future extensions.

Contains additional microSD card socket.

Used to connect other boards

Theremin Pitch and Volume sensor oscillators
TFT Touch Screen
Encoders board
Expression pedals board
Audio I/O PMods: I2S2 and AMP3

Design

The purpose of Theremin Shield is intefacing between FPGA board and peripherials.

The only peripherial placed on shield is MicroSD card socket.

The rest of peripherials are being connected via various connectors.

Based on chosen hardware components, it's necessary to plan available FPGA board pin usage.

Waveshare 4.3" 800x480 TFT Capacitive Touch Screen

TFT Touch screen with RGB interface requires a lot of FPGA pins. Only RGB data needs 24 (8 * 3) pins.

To minimize FPGA board pins usage for TFT, it was decided to reduce color resolution of display from 8 to 4 bits per component. Lower 4 pins of each component are wired to upper 4 bits. This approach allows to keep full range 0x00..0xff of component values equally distributed with 0x11 step - instead of 0x00..0xf0 if it decided to set lower components to 0.

Although LCD Touch screen allows to control virtually any device features, often it's feasible to have hardware controls. There is Encoders board with 5 incremental encoders and one button. Multiplexing is used to reduce number of required pins from 16 to 5.

There are 6 single ended analog inputs (ADC) on Cora Arduino/Chipkit connectors. They can be used as analog inputs from pot based pedals (expression pedals).

Since there were several unused pins on FPGA board after assignment of main peripherial devices, I decided to add MicroSD Card on shield.

Display supports both FPC and IDC connectors. Both types of connectors are traced on shield PCB. Although, FPC/FCC connector is really hard to solder. Probably, it makes sense to use IDC.

LCD interface pin assignment: IDC40 connector (J1)

Please note: odd/even pins are mirrored comparing with Waveshare LCD pins assignment

LCD pin header	Cora Z7 pin	Signal	Direction
Touch controller
1	IO41	Touch IRQ	Input
2	5V5	+5V	Power Output
3	n/c	n/c	n/c
4	SDA	Touch I2C SDA	Bidirectional
5	SCL	Touch I2C SCL	Output
6	IO40	Touch Reset	Output
Backlight control
7	IO5	LCD Backlight PWM	Output
8	GND	GND	Power Output
9	n/c	n/c	n/c
10	n/c	n/c	n/c
Red data
11	IO13	R0 = R4	Output
12	IO39	R1 = R5	Output
13	IO12	R2 = R6	Output
14	IO38	R3 = R7	Output
15	IO13	R4	Output
16	IO39	R5	Output
17	IO12	R6	Output
18	IO38	R7	Output
Green data
19	IO11	G0 = G4	Output
20	IO37	G1 = G5	Output
21	IO10	G2 = G6	Output
22	IO36	G3 = G7	Output
23	IO11	G4	Output
24	IO37	G5	Output
25	IO10	G6	Output
26	IO36	G7	Output
Blue data
27	IO9	B0 = B4	Output
28	IO35	B1 = B5	Output
29	IO8	B2 = B6	Output
30	IO34	B3 = B7	Output
31	IO9	B4	Output
32	IO35	B5	Output
33	IO8	B6	Output
34	IO34	B7	Output
LCD clock and control signals
35	IO7	PXCLK - pixel clock	Output
36	+3.3V via 10K R	DISP - display enable	Output
37	IO33	HSYNC - horizontal sync	Output
38	IO6	VSYNC - vertical sync	Output
39	IO32	DE - data enable	Output
20	GND	GND	Power Output

PMod adapters

PMod connectors for I2S2 and AMP3 PMods are made using custom pmod adapter boards - to place PMods above shield.

There are two audio PMODs used in this theremin design

I2S2 pmod: Line In + Line Out: one stereo input and one stereo output
AMP3 pmod: Phone Out Amplifier: one stereo output and I2C interface to control apmlifier parameters

I2S interface of both pmods reuse the same clocking signals: MCLK (master clock), WS(RLLK), SCLK(data clock)

I2S2 PMod uses 2 data pins - one for line in data, one for line out data

AMP3 PMod uses 1 data pin - out data to phones. Additionally it uses I2C interface for controlling.

PMod I2S2 connector (J8)

I2S2 pmod pin	Cora Z7 pin	Signal	Direction
1	IO3	Line Out MCLK = Line In MCLK	Output
2	IO29	Line Out LRCK = Line In LRCK (WS)	Output
3	IO2	Line Out SCLK = Line In SCLK	Output
4	IO28	Line Out data	Output
5	GND	GND	Power Output
6	+3.3V	+3.3V	Power Output
7	IO3	Line In MCLK = Line Out MCLK	Output
8	IO29	Line In LRCK = Line Out LRCK (WS)	Output
9	IO2	Line In SCLK = Line Out SCLK	Output
10	IO1	Line In data	Input
11	GND	GND	Power Output
12	+3.3V	+3.3V	Power Output

PMod AMP3 connector (J9)

AMP3 pmod pin	Cora Z7 pin	Signal	Direction
1	IO29	LRCK (WS)	Output
2	IO30	out data	Output
3	n/c	n/c	n/c
4	IO2	SCLK	Output
5	GND	GND	Power Output
6	+3.3V	+3.3V	Power Output
7	IO31	I2C SDA	Bidirectional
8	IO4	I2C SCL	Output
9	IO3	MCLK	Output
10	+3.3V via 10K R	nSD	Output
11	GND	GND	Power Output
12	+3.3V	+3.3V	Power Output

Oscillator connectors

To connect each of two oscillators it's necessary to use one input pin

Pitch oscillator connector (J7)

Connector pin	Cora Z7 pin	Signal	Direction
1	GND	GND	Power Output
2	IO0	Pitch oscillator signal	Input
3	+3.3V	+3.3V	Power output

Volume oscillator connector (J6)

Connector pin	Cora Z7 pin	Signal	Direction
1	GND	GND	Power Output
2	IO42	Volume oscillator signal	Input
3	+3.3V	+3.3V	Power output

Encoders board connector (J4)

Multiplexing is used to reduce number of used pins.

There are 5 incremental encoders with buttons and 1 tact button on Encoders board. They give 16 output signals.

To decrease number of used FPGA pins, multiplexing is used. Address A0..A3 selects signal to get value from. MUX out provides value of signal which index is set to A0..A3 pins.

Differencial ACD input pins are used as digital I/O for encoders board connection.

Connector pin	Cora Z7 pin	Signal	Direction
1	A7	MUX output	Input
2	n/c	n/c	n/c
3	A8	A0 mux address	Output
4	A9	A1 mux address	Output
5	A10	A2 mux address	Output
6	A11	A3 mux address	Output
7	+3.3V	+3.3V	Power output
8	GND	GND	Power Output

Analog pedals board connector (J5)

Additional controlls may be connected using 6 on-board single-ended ADC analog input pins.

Connector pin	Cora Z7 pin	Signal	Direction
1	A0	Analog In 1	Analog Input
2	A1	Analog In 2	Analog Input
3	A2	Analog In 3	Analog Input
4	A3	Analog In 4	Analog Input
5	A4	Analog In 5	Analog Input
6	A5	Analog In 6	Analog Input
7	+3.3V	+3.3V	Power output
8	GND	GND	Power Output

MicroSD Card socket (J3)

MicroSD socket is traced on theremin shield PCB.

uSD card pin	Cora Z7 pin	Signal	Direction
1	IO27	DAT2	Bidirectional
2	IO26	DAT3/CD	Bidirectional
3	SPI SS	CMD	Bidirectional
4	+3.3V	+3.3V	Power Output
5	SPI SCLK	CCLK	Output
6	GND	GND	Power Output
7	SPI MISO	DAT0	Bidirectional
8	SPI MOSI	DAT1	Bidirectional
9	A6	Card Detect B	Input
10	GND	Card Detect A	Power Output

PCB design

Schematic and PCB are designed in KiCAD.

Board	KiCAD Schematic	Gerber file
Cora Z7 Theremin Shield Connected to Cora Z7 board using Arduino/Chipkit connector.

FPGA part

TBD

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