"practically smallest" debug connector on tiny pcb - Page 1
Forum section: electronics / projects

author: Wilson__
author_rank: Frequent Contributor
timestamp: April 24, 2024, 08:11:19 pm
content: Appreciate advises on a 'practically smallest' connector on custom made PCB. For connection to ST-Link debugger 10 pins. Seem FPC is nice (flex printed circuit board as in Raspberry Pi camera) with a flip tab so FPC cable can be inserted with zero force and last for tens of insert/uninsert cycles. What are the going-to pitch that is easily available, 1mm or 0.5mm or others? Many thanks

author: jc101
author_rank: Frequent Contributor
timestamp: April 24, 2024, 08:36:56 pm
content: Presume all thehttps://www.tag-connect.com/productsare too large?

author: langwadt
author_rank: Super Contributor
timestamp: April 24, 2024, 08:48:35 pm
content: Quote from: Wilson__ on April 24, 2024, 08:11:19 pmwhy 10 pins? SWD debug only really need two pins plus gnd

author: ataradov
author_rank: Super Contributor
timestamp: April 24, 2024, 09:01:01 pm
content: First of all, reduce the number of pins. In addition to the SWD+GND you may need VCC for powering the debugger buffers, and may be reset. So, at most you need 5 pins.And then the smallest connector is just 0.05" though hole header. It can be populated with an actual connector or wires soldered to a more useful connector. It can also be used as test points for mass production.For the same small number of contacts, FPC connectors end up being bigger, since they need mechanical pads as well.

author: PCB.Wiz
author_rank: Super Contributor
timestamp: April 24, 2024, 09:13:45 pm
content: Quote from: Wilson__ on April 24, 2024, 08:11:19 pmOne approach I've seen for tight boards, is to extend the debug / program header off-board into a break-off tongue, that is used for development and program, but that is broken off when the board goes into the final case.Pogo pin pads can be provided, if you need subsequent physical contact firmware updates.

author: Wilson__
author_rank: Frequent Contributor
timestamp: April 24, 2024, 10:10:11 pm
content: yes, many thanks. 0.05 inch through hole look good. if one row, it can contact plate through hole with some bend force. swdio, swclk, gnd, vcc, nrst is 5 pins. the new swo not tried before, is one more pin. Document says spy on the mcu but need graphic programming on the debug pc to extract useful data. may not be too useful as now. for luxery, uart tx, rx will be 8.

author: Wilson__
author_rank: Frequent Contributor
timestamp: April 24, 2024, 10:12:16 pm
content: many thanks. very good thinking. snap off to 0.1 inch connector and on board hole or poco pin pads at 0.05 inch

author: ataradov
author_rank: Super Contributor
timestamp: April 24, 2024, 10:20:35 pm
content: You don't need SWO for programming. It may be useful for debugging, but in most cases it is not worth it, especially if you already have debug UART.

author: Wilson__
author_rank: Frequent Contributor
timestamp: April 24, 2024, 10:46:18 pm
content: Many thanks. Very clever way to do it. Castellated board edge takes little space on pcb

author: Kasper
author_rank: Frequent Contributor
timestamp: April 27, 2024, 03:54:10 am
content: If you include an extra pin, you can use it as a key, to reduce the chance of someone plugging the programmer in backwards.