7 ms·

In a similar vein, I discovered and have started using the Tag-Connect TC2030-USB to program/troubleshoot my boards. While it's technically/originally intended

In a similar vein, I discovered and have started using the Tag-Connect TC2030-USB to program/troubleshoot my boards. While it's technically/originally intended as a way to do JTAG debugging, I am completely enamored with the ability to drop a footprint on my PCB and be able to connect to it without having to place a relatively expensive connector (or a connector at all) that I don't necessarily want users interacting with. https://www.tag-connect.com/solutions-target-devices/usb-serial https://www.tag-connect.com/solutions-target-devices/usb-ser... They have FTDI versions as well, for those who want the full USB boot/reset treatment. Also, they have another connector for attaching to castellated edges. I think it's just so clever.

Brian_K_White 1y ago
I just use ordinary straight pin headers and stagered via holes. The board just has vias and the cable just has a plain pin header not even pogo pins.
- stavros 1y ago
  Why vias? So the pins don't go all the way through? Wouldn't any disparity in the lengths of the pins make that pin not touch?
  - azdle 1y ago
    I think they probably mean standard through-holes. It's the old trick where you stagger the holes just enough that the flex of the pinheaders still let's them be inserted, but have just enough friction to stay in place while you're flashing or whatever.
    - stavros 1y ago
      Oooh that's a great trick! Thanks, I'll try that on my next board.
    - Brian_K_White 1y ago
      Right, plated through holes, but with almost no exposed anular ring. As little as I can get away with without getting mask sprayed down into the hole. For 100 mil pitch, 25 mil square pins: 36 mil holes, 6 mil off center, 12 mil hole to hole. The short side of a generic pin header is the side that goes in the holes, so the long side is free to accept dupont sockets and shunts the same as if you had the same pins soldered in the pcb. So the cable is just ordinary programmer fly wires with female dupont ends. You don't even need to make an actual cable. If space is tight on the pcb then it does use up more pcb than pads that leave the other side free. And pogo pins are going to be a lot faster for producing something in numbers. I don't mind buying nice stuff like a fancy purpose made good-working tool for myself but I'm always making open source projects and one design goal is to require as little as possible, and as generic and universal as possible from the user. So I avoid fancy special things where possible. It's not designing for commercial production runs nor designing for one-off for myself, it's designing to a kind of a platonic ideal to strip away anything unnecessary and yet try to meet 2 opposing goals at the same time as much as possible: Don't require special tools that make things work reliably because of how fancy the tool is, and don't require the user to be a zen master craftsman that can attain a successful result with rocks and nails. Try to make the process reliable and repeatable while still only requiring basic materials and supplies. As much as possible anyway. Pogo pins are pretty common these days and not exactly exotic or expensive any more so maybe I can start using them. Then again, the through holes do 2 extra things besides make the connection. With pads you need to aim/register the pins to land on the pads, and you need to hold them there. That means aiming with your eyes and holding with at least one hand, or it means adding some kind of extra registration and grabbing features to both the pcb and the cable, like extra drill holes or slots and extra plastic shapes on a special cable-end etc. Or no extra features on the board and instead a whole clamping jig that holds both the board and the pins. Since these are holes that pins go in to, you don't need any other form of registration to aim the pins at the pads. The pins go in the holes. And they hold onto the pins themselves, so you don't need any other form of retention. It's just like plugging a plug into a socket where the socket provides all that naturally. I have one board that needs two different connections like that, one for jtag and one for power and to temporarily close a jumper to write-enable the cpld. So a 4-pin and a 6-pin, 2 different cables in 2 different places. The entire board is slightly smaller than a DIP-28 so no room for any real connectors. You just stick the cables in and two different cables hold themselves with zero hands while you operate the flashing software. The wires are all plain dupont wires stuck on the pins, no solder, and 2 of the pins just have a generic jumper on them. It's completely basic and not-special and works perfect. I have another board that needs 28 pins in a small space. For that one I used 2.0mm pitch pins in straight rows not staggered, but with the holes only 1.7mm apart. In that case it's the long side of the pins that goes into the holes, and the short side is soldered into a programming adapter pcb that goes into a programmer. The pins are in 2 sets of 2x7. Each set of 2x7 has 2 straight rows of 0.72mm holes 1.7mm apart. What happens there is, as the pins start to lean over, the top of the pins hit the opposite side of the hole on the top of the pcb, and don't want to go any further. The pins wedge solid and make 4 points of contact, 2 on bottom and 2 on top, and the board won't go any further even though the pins only just poke out the top and there is still almost 2mm of travel left. So you have a lot of remaining travel to just push a little more if you get a bad connection. It works great and no special parts anywhere.
wrs 1y ago
I've been doing a cheap DIY version of Tag-Connect for some STM32 projects (6-pin debug). I just put the holes for a pin header near the edge of the board, and use a pogo clip to connect [0]. (These are readily available on AliExpress in various sizes.) [0] https://www.adafruit.com/product/5433 https://www.adafruit.com/product/5433
- edanuff 1y ago
  I do exactly the same on my boards and use that same clip.
  - sam_bristow 1y ago
    Back in my undergrad days I built a similar clip out of a broken clothes peg, hot glue, and some 2.54mm headers. It worked well.
jkestner 1y ago
Same, enamored and I’m not even the EE. Elegant, no cost on the product side, and I don’t have to take the board out of the case to access it.
exmadscientist 1y ago
They're fine for one guy using them on the bench but they are a nightmare for mass production. The 50-mil pitch is annoying to make work with a bed-of-nails fixture, the clips are fundamentally incompatible with production lines, either robot or human, the parts are expensive, and the cycle life is not there. I have had one too many arguments with firmware people who think these things are sufficient for production that I am just done with them by now. There are other ways to do it.
- pidge 1y ago
  Out of curiosity what are the other ways?
  - BertoldVdb 1y ago
    Just put normal test pads next to the tag connect, a bit more spaced out. A bed of nails in the production line connects to that, the tag connect can be used for bench development.
    - scld 1y ago
      This is the way
  - davidzweig 1y ago
    0.1" header holes slightly staggered to grip inserted headers can work great and you don't need to have a special expensive cable on hand to use it.
- ACCount37 1y ago
  This reads like a skill issue to me. The only actual issue I had with Tag is that it takes up more space than an array of aggressively placed test points would. Which is still acceptable in some designs. If you can't hit a massive, enormous 1.27mm pitch connector complete with dedicated indexing holes with your jig, I can't fathom how that would be the fault of the connector.
mmoskal 1y ago
I had good experience with carefully spaced holes in PCB and a 50 mil header, see https://jacdac.github.io/jacdac-docs/ddk/firmware/jac-connect/ https://jacdac.github.io/jacdac-docs/ddk/firmware/jac-connec...
- amelius 1y ago
  You might be interested in this "SKEDD" connector: https://www.we-online.com/katalog/media/o210254v410%20ANE011b_EN.pdf https://www.we-online.com/katalog/media/o210254v410%20ANE011... https://www.digikey.com/en/products/detail/w%C3%BCrth-elektronik/490107670412/7917216 https://www.digikey.com/en/products/detail/w%C3%BCrth-elektr...
_Microft 1y ago
Maybe you like this - "paw connect", a whimsical version of the footprint for this connector: https://github.com/LeoDJ/Paw-Connect https://github.com/LeoDJ/Paw-Connect
the__alchemist 1y ago
I wish the cables weren't so expensive! They do wear out after a while; had one die that way. Using the 2030-NL STM32 6-pin one.

Brian_K_White 1y ago

I just use ordinary straight pin headers and stagered via holes. The board just has vias and the cable just has a plain pin header not even pogo pins.

stavros 1y ago
Why vias? So the pins don't go all the way through? Wouldn't any disparity in the lengths of the pins make that pin not touch?
- azdle 1y ago
  I think they probably mean standard through-holes. It's the old trick where you stagger the holes just enough that the flex of the pinheaders still let's them be inserted, but have just enough friction to stay in place while you're flashing or whatever.
  - stavros 1y ago
    Oooh that's a great trick! Thanks, I'll try that on my next board.
  - Brian_K_White 1y ago
    Right, plated through holes, but with almost no exposed anular ring. As little as I can get away with without getting mask sprayed down into the hole. For 100 mil pitch, 25 mil square pins: 36 mil holes, 6 mil off center, 12 mil hole to hole. The short side of a generic pin header is the side that goes in the holes, so the long side is free to accept dupont sockets and shunts the same as if you had the same pins soldered in the pcb. So the cable is just ordinary programmer fly wires with female dupont ends. You don't even need to make an actual cable. If space is tight on the pcb then it does use up more pcb than pads that leave the other side free. And pogo pins are going to be a lot faster for producing something in numbers. I don't mind buying nice stuff like a fancy purpose made good-working tool for myself but I'm always making open source projects and one design goal is to require as little as possible, and as generic and universal as possible from the user. So I avoid fancy special things where possible. It's not designing for commercial production runs nor designing for one-off for myself, it's designing to a kind of a platonic ideal to strip away anything unnecessary and yet try to meet 2 opposing goals at the same time as much as possible: Don't require special tools that make things work reliably because of how fancy the tool is, and don't require the user to be a zen master craftsman that can attain a successful result with rocks and nails. Try to make the process reliable and repeatable while still only requiring basic materials and supplies. As much as possible anyway. Pogo pins are pretty common these days and not exactly exotic or expensive any more so maybe I can start using them. Then again, the through holes do 2 extra things besides make the connection. With pads you need to aim/register the pins to land on the pads, and you need to hold them there. That means aiming with your eyes and holding with at least one hand, or it means adding some kind of extra registration and grabbing features to both the pcb and the cable, like extra drill holes or slots and extra plastic shapes on a special cable-end etc. Or no extra features on the board and instead a whole clamping jig that holds both the board and the pins. Since these are holes that pins go in to, you don't need any other form of registration to aim the pins at the pads. The pins go in the holes. And they hold onto the pins themselves, so you don't need any other form of retention. It's just like plugging a plug into a socket where the socket provides all that naturally. I have one board that needs two different connections like that, one for jtag and one for power and to temporarily close a jumper to write-enable the cpld. So a 4-pin and a 6-pin, 2 different cables in 2 different places. The entire board is slightly smaller than a DIP-28 so no room for any real connectors. You just stick the cables in and two different cables hold themselves with zero hands while you operate the flashing software. The wires are all plain dupont wires stuck on the pins, no solder, and 2 of the pins just have a generic jumper on them. It's completely basic and not-special and works perfect. I have another board that needs 28 pins in a small space. For that one I used 2.0mm pitch pins in straight rows not staggered, but with the holes only 1.7mm apart. In that case it's the long side of the pins that goes into the holes, and the short side is soldered into a programming adapter pcb that goes into a programmer. The pins are in 2 sets of 2x7. Each set of 2x7 has 2 straight rows of 0.72mm holes 1.7mm apart. What happens there is, as the pins start to lean over, the top of the pins hit the opposite side of the hole on the top of the pcb, and don't want to go any further. The pins wedge solid and make 4 points of contact, 2 on bottom and 2 on top, and the board won't go any further even though the pins only just poke out the top and there is still almost 2mm of travel left. So you have a lot of remaining travel to just push a little more if you get a bad connection. It works great and no special parts anywhere.

wrs 1y ago

I've been doing a cheap DIY version of Tag-Connect for some STM32 projects (6-pin debug). I just put the holes for a pin header near the edge of the board, and use a pogo clip to connect [0]. (These are readily available on AliExpress in various sizes.) [0] https://www.adafruit.com/product/5433 https://www.adafruit.com/product/5433

edanuff 1y ago
I do exactly the same on my boards and use that same clip.
- sam_bristow 1y ago
  Back in my undergrad days I built a similar clip out of a broken clothes peg, hot glue, and some 2.54mm headers. It worked well.

jkestner 1y ago

Same, enamored and I’m not even the EE. Elegant, no cost on the product side, and I don’t have to take the board out of the case to access it.

exmadscientist 1y ago

They're fine for one guy using them on the bench but they are a nightmare for mass production. The 50-mil pitch is annoying to make work with a bed-of-nails fixture, the clips are fundamentally incompatible with production lines, either robot or human, the parts are expensive, and the cycle life is not there. I have had one too many arguments with firmware people who think these things are sufficient for production that I am just done with them by now. There are other ways to do it.

pidge 1y ago
Out of curiosity what are the other ways?
- BertoldVdb 1y ago
  Just put normal test pads next to the tag connect, a bit more spaced out. A bed of nails in the production line connects to that, the tag connect can be used for bench development.
  - scld 1y ago
    This is the way
- davidzweig 1y ago
  0.1" header holes slightly staggered to grip inserted headers can work great and you don't need to have a special expensive cable on hand to use it.
ACCount37 1y ago
This reads like a skill issue to me. The only actual issue I had with Tag is that it takes up more space than an array of aggressively placed test points would. Which is still acceptable in some designs. If you can't hit a massive, enormous 1.27mm pitch connector complete with dedicated indexing holes with your jig, I can't fathom how that would be the fault of the connector.

mmoskal 1y ago

I had good experience with carefully spaced holes in PCB and a 50 mil header, see https://jacdac.github.io/jacdac-docs/ddk/firmware/jac-connect/ https://jacdac.github.io/jacdac-docs/ddk/firmware/jac-connec...

amelius 1y ago
You might be interested in this "SKEDD" connector: https://www.we-online.com/katalog/media/o210254v410%20ANE011b_EN.pdf https://www.we-online.com/katalog/media/o210254v410%20ANE011... https://www.digikey.com/en/products/detail/w%C3%BCrth-elektronik/490107670412/7917216 https://www.digikey.com/en/products/detail/w%C3%BCrth-elektr...

_Microft 1y ago

Maybe you like this - "paw connect", a whimsical version of the footprint for this connector: https://github.com/LeoDJ/Paw-Connect https://github.com/LeoDJ/Paw-Connect

the__alchemist 1y ago

I wish the cables weren't so expensive! They do wear out after a while; had one die that way. Using the 2030-NL STM32 6-pin one.