Custom STM32H750 embedded development board

Introduction #

When doing embedded systems development, it can sometimes be hard to find a development board with the desired features at an affordable price. A solution to this is to learn how to design and manufacture your own custom development boards.

This project is my first custom development board. It features :

the STM32H750VBT6TR MCU containing an ARM cortex-m7 core;
an SWD debug interface with a pinout compatible with the 20 pin J-Link probe;
an USB-B mini connector;
a Micro SD card connector.

Essenceia/stm32h750-dev-board

Small embedded dev board with an STM32H7 and a full J-link connector

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The USB’s data transfer functionality and the SD card reader have not been tested as of writing. I suggest double checking the PCB schematics for these if you intend to use them in your own project.

An anniversary present #

I met my wonderful husband over 10 years ago, we were high school love birds. Today he is a talented low level C developer that writes kernels for fun.

He likes targeting microcontrollers but was often disappointed by the lack of proper JTAG or SWD debugging interface on all the development boards he owned.

As such, this board was made as my 10 year anniversary present to him.

Debug interface #

One of the goals on this design is to be able to directly plug the debug probe onto the board without the need for any additional adapter.

schematics — Board connected to our J-Link

J-Link connector pinout #

We are using a J-Link as our debug probe. It has a 20 pin connector and supports SWD using the following connector pinout:

J-Link connector pinout for SWD

The following table lists the J-Link / J-Trace SWD pinout.

Pin	Signal	Type	Description
1	VTref	Input	This is the target reference voltage. It is used to check if the target has power, to create the logic-level reference for the input comparators and to control the output logic levels to the target. It is normally fed from Vdd of the target board and must not have series resistors.
2	Vsupply	NC	This pin is not connected in the J-Link. It is reserved for compatibility with other equipment. Connect to Vdd or leave it open in target system.
3	Not used	NC	This pin is not used by the J-Link. If the device may also be accessed via JTAG, this pin may be connected to nTRST, otherwise leave it open.
5	Not used	NC	This pin is not used by the J-Link. If the device may also be accessed via JTAG, this pin may be connected to TDI, otherwise leave it open.
7	SWDIO	I/O	Single bi-directional data pin.
9	SWCLK	Output	Clock signal to target CPU. It is recommended that this pin is pulled to a defined state of the target board. Typically connected to TCK of target CPU.
11	Not used	NC	This pin is not used by the J-Link. This pin is not used by J-Link when operating in SWD mode. If the device may also be accessed via JTAG, this pin may be connected to RTCK, otherwise leave it open.
13	SWO	Input	Serial Wire Output trace port. (Optional, not required for SWD communication.)
15	nRESET	I/O	Target CPU reset signal. Typically connected to the RESET pin of the target CPU, which is typically called “nRST”, “nRESET” or “RESET”. This signal is an active low signal.
17	Not used	NC	This pin is not connected in the J-Link.
19	5V-Supply	Output	This pin is used to supply power to some eval boards.

Pins 4, 6, 8, 10, 12, 14, 16, 18, 20 are GND pins connected to GND in J-Link. They should also be connected to GND on the board.

jlink pcb bir — J-Link connections to the board.

All SWD J-Link pins are connected with the exception of the 5V-Supply, as even when the debug probe is connected power is still gotten from the USB.

Mounting the connector to the PCB #

The connector should be mounted with the slot facing up, away from the MCU as shown below.

CAD #

This board was designed using Kicad 7.0.8 and all project files are available for download in the following github repository.

Schematic #

Full schematics of the board :

PCB #

Computer rending of the PCB :

Final result :

pcb — Unmounted spare PCB’s, will be used for version 2.

Bill of Materials #

Item #	Designator	Qty	Manufacturer	Mfg Part #	Description / Value	Package/Footprint	Type	Your Instructions / Notes
1	DC6,DC3,DC5,DC4,DC8,DC9,DC7,DC11,DC1,DC2	10	KEMET	C0402C104K4RAC	100nF	0402	SMD
2	U3	1	Texas Instruments	TLV1117-33CDCYRG3	TLV1117-33	SOT-223	SMD
3	R4,R5,R3	3	SEI Stackpole	RMCF0603JJ1K00	1k	0603	SMD
4	Y2	1	ECS Inc.	ECS-250-9-37B2-CKM-TR	25MHz 9uF	2.0x1.6mm	SMD
5	R15,R14,R13,R7,R16,R12,R10,R11	8	YAGEO	RC0402FR-0710KL	10k	0402	SMD
6	U1	1	STMicroelectronics	STM32H750VBT6TR / STM32H742VIT6	STM32H750VBTx / STM32H742VI	LQFP-100	QFP	MCU for v1 and v2, pin compatible
7	J2	1	On Shore Technology Inc.	302-S201	Conn_ARM_JTAG_SWD_20	THD	Through Hole
8	C8,C5,C6,C7,C1,C2	6	Samsung Electro-Mechanics	CL31A476MQHNNNE	47uF/3528	1206	SMD
9	D2,D1	2	EVERLIGHT	19-213SYGC/S530-E2/5T	LED	0603	SMD
10	R1,R2	2	YAGEO	RC0402FR-0722RL	22	0402	SMD
11	R6,R8	2	SEI Stackpole	RMCA0603JT510R	510	0603	SMD
12	C4,C3	2	Murata Electronics	GJM1555C1H8R0DB01D	8pF	0402	SMD
13	J3	1	Molex	1040310811	Micro_SD_Card_Det1		SMD
14	D3	1	Toshiba	CRS30I40A(TE85L,QM	SS34	SOD-123F	SMD
15	L1,L2	2	TAI-TECH	FCM1608KF-102T02	1KB	0603	SMD
16	SW1	1	C&K	PTS636 SM43 SMTR LFS	SW_RESET	6.0x3.5mm	SMD
17	U2	1	STMicroelectronics	USBLC6-2P6	USBLC6-2P6	SOT-666	SMD
18	J1	1	Adam Tech	MUSB-B5-S-RA-SMT-PP-T/R	USB_B_Mini		SMD
19	J4,J5	2	Sullins Connector Solutions	PPTC252LFBN-RC	Conn_02x25_Odd_Even		Through Hole

For reference, I recently ordered components for 3 version 2 boards in Canada and spent 107 CAD at Mouser.

Version 2 #

Now that the first version is up and running it is time to start thinking of improvements for the second version.

The first revision of the board uses the STM32H750VBT6TR MCU, which only has 128kB of flash. Now that I have confirmed that the board is working it is time to upgrade to something with more flash.

This new revision will keep the existing PCB and components but drop in the STM32H742VIT6 as the MCU. This MCU features 2 MB of flash, 1 MB of RAM and is otherwise the same chip with regards to the features that matter to us.