Overview

A capacitive touch sensing USB device.

A 32-bit version/descendant of the Cocomake7.

A work in progress prototype to learn more about ARM dev, STM32 peripherals and compare results with the AVR and teensy based versions.

The goal is to make a versatile, affordable and playful interface device, that can be used as a creative basis for interactive (non-usb) playthings, DIY projects and electronics/interaction/game dev workshops.

Hardware

General Notes

Microcontroller:

STM32F042F6P6
Crystal-less USB with integrated USB (fullspeed) PHY
Capacitive touch sensing peripheral
Cost: ~$2 on Aliexpress (Chips Store)

Revision 0.03

A test PCB with 6 touch pads lined up in a row. Easy to breakout, by cutting the PCB traces...

No USB (ESD) protection, no line termination resistors (D+/-), no filtering, optimized for simplicity, size and cost.

Features

6 touchpads
micro USB port
debug LED
I2C / SWD connector

BOM

Reference	Value		Footprint		Digikey				Comment		Count	Unit Cost	SUM

rawcoco:U1	STM32F042F6Px	w_smd_dil:tssop-20	STM32F042F6P6-ND		not available	1	1.48 EUR	1.48 EUR
rawcoco:U2	TLV70033DDCR	w_smd_trans:sot23-5	296-27937-1-ND					1	0.48 EUR	0.48 EUR
							
rawcoco:C1	100n		mylib:c_0402_mod0	490-10777-1-ND					1	0.09 EUR	0.09 EUR
rawcoco:C8 C9	1u		mylib:c_0603_mod0	490-6423-1-ND 					2	0.09 EUR	0.18 EUR
rawcoco:C10 C11	1n		mylib:c_0402_mod0	490-6349-1-ND					2	0.09 EUR	0.18 EUR
							
rawcoco:D1	LED		w_smd_leds:Led_0402	511-1651-1-ND					1	0.41 EUR	0.41 EUR
							
rawcoco:R1	470R		mylib:r_0402_mod0	CR0402-FX-4700GLFCT-ND 	470 Ohm			1	0.09 EUR	0.09 EUR
rawcoco:R7-R12	1k		mylib:r_0402_mod0	CR0402-FX-1001GLFCT-ND				6	0.09 EUR	0.54 EUR
							
rawcoco:CON1	USB-MINI-B_mod0	mylib:conn_usb_B_micro_smd-2_mod0wHoles	WM17141CT-ND			1	0.91 EUR	0.91 EUR
							
rawcoco:K1 K2	CONN_3		mylib:pin_header_3x1_1.27mm_pitch					2	0.00 EUR	0.00 EUR
rawcoco:P1 P2	CONN_4		mylib:pin_header_4x1_1.27mm_pitch					2	0.00 EUR	0.00 EUR
rawcoco:P4-P6	CONN_1		mylib:pin_header_1x1_1.27mm_pitch					3	0.00 EUR	0.00 EUR

											SUM		22			4.36 €

Digikey BOM (MCU not included):

1,296-27937-1-ND,rawcoco:U2
1,490-10777-1-ND,rawcoco:C1
2,490-6423-1-ND ,rawcoco:C8 C9
2,490-6349-1-ND,rawcoco:C10 C11
1,511-1651-1-ND,rawcoco:D1
1,CR0402-FX-4700GLFCT-ND ,rawcoco:R1
6,CR0402-FX-1001GLFCT-ND,rawcoco:R7-R12
1,WM17141CT-ND,rawcoco:CON1

PCB

Get it at: OSHPark

Pinouts

SWD Pinout (topview, USB plug on the left):

VDD
SWCLK
VSS
SWDIO

Touchpad (TSC) order (topview, USB plug on the left):

G1_IO4
G1_IO3
G1_IO2
G2_IO4
G2_IO3
G2_IO2

Errata / Known Bugs

tie PB8 to ground -> BOOT0

Software

Currently used/evaluated tools and sources to get the board up and running:

Free tools for ARM development (gcc-none-eabi toolchain, OpenOCD)
STM32CubeMX and sample code by ST
Code::Blocks as an IDE

More notes are collected here...

USB HID Device

Status: Mouse, Keyboard, Gamepad HID devices are working.

The generated code from STM32CubeMX was really helpful here. The HID report descriptor had to be modified in order to get keyboard and gamepad recognized by the OS.

This tutorial was helpful: http://eleccelerator.com/tutorial-about-usb-hid-report-descriptors/

The official doc as well: http://www.usb.org/developers/hidpage/HID1_11.pdf

The HID Descriptor Tool there comes with good examples and a validator plus exporter (header file...): http://www.usb.org/developers/hidpage/

Keyboard Test

This is the current test setup to send out keyboard keys from A-F. All six keys can be pressed at once... Funny, that the Keyboard HID descriptor can store six keys at max...

Current problem: The sensitivity of the keys and fine tuning of the TSC peripheral needs to be investigated more...