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Building the worlds jankiest serial to USB cable from scavenged parts

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Re: Building the worlds jankiest serial to USB cable from scavenged parts

#21

Post by tomn »

crispyambulance wrote: post #13

tldr; for those who didn't bother to look for "an explanation" of why the wires were soldered directly to the pins of the IC instead of THE BREAK-OUT BOARD... > Now, you're probably thinking to yourself: "Why would you not just solder to the nice, big, widely spaced holes for the pin headers?", which is a fair question. I suppose this the one place I opted for a little less jank. You see, differential pairs actually…

This could end up being worse from a signal-integrity point-of-view, as now both of those traces have a stub (of different lengths!), which will comb-filter the signal.

If you wanted to be fancy, it would have been better to lift those two pins, or to cut the traces.

All this is completely unnecessary given the speeds involved (12Mbit/s) and possible skew or stub lengths, which they acknowledge.

Re: Building the worlds jankiest serial to USB cable from scavenged parts

#22

Post by ajsnigrutin »

alias_neo wrote: post #4

I'm not sure why I expected more, but I was a little disappointed. Soldering some wires onto an FTDI chip in a pinch is great, but the chip is doing all of the work really. I was hoping to learn I could make a serial to USB with _less than_ an FTDI chip. That said, respect for the effort of taking the photos and writing it up, and it was worth a read to learn about those naughty Scots bricking peoples devices with ba…

USB is hard... you need a chip to deal with it. "Back in my day", you could bitbang stuff with a parallel port, but those days are gone.

I would've picked a more lazy approach, just pull the atmega chip from an arduino (to not cause issues), and use the rx and tx pins on the (now empty) arduino board, since they're both connected to ftdi chip already, and no de/soldering is needed.

Re: Building the worlds jankiest serial to USB cable from scavenged parts

#23

Post by MarkusWandel »

No need to junk a perfectly good Arduino for that. Just load a trivial sketch that disables the Arduino's TX pin and just access the serial link through the D0 (RX0) and D1 (TX0) pins. Reversed of course; what's RX to the Arduino is TX to the serial chip.

Re: Building the worlds jankiest serial to USB cable from scavenged parts

#24

Post by fstokesman »

MarkusWandel wrote: post #23

No need to junk a perfectly good Arduino for that. Just load a trivial sketch that disables the Arduino's TX pin and just access the serial link through the D0 (RX0) and D1 (TX0) pins. Reversed of course; what's RX to the Arduino is TX to the serial chip.

This is the most use that board has and would have gotten in the last 10+ years. I like to think it laying down its FTDI chip for a greater cause was an honour for it.

Re: Building the worlds jankiest serial to USB cable from scavenged parts

#25

Post by alias_neo »

fstokesman wrote: post #15
alias_neo wrote: post #4

I'm not sure why I expected more, but I was a little disappointed. Soldering some wires onto an FTDI chip in a pinch is great, but the chip is doing all of the work really. I was hoping to learn I could make a serial to USB with _less than_ an FTDI chip. That said, respect for the effort of taking the photos and writing it up, and it was worth a read to learn about those naughty Scots bricking peoples devices with ba…

Totally fair point. One of the videos I'm going to get around to making on my channel at some stage is a UART transceiver on an FPGA. Definitely not the "easier in a pinch" I was originally going for, but hey, if you've got the hardware hanging around!

I didn't mean for that to come across as a criticism, I was disappointed because I was hoping to learn something new, but I'm not the target for that post; I have a degree in Electronic Engineering and a couple of decades of tinkering.

I'll be interested in some FPGA content; I built my dissertation project on FPGA and would love to see some modern, affordable FPGA boards/circuits with useful I/O to actually build something like this. I'm sure they exist, I've just never looked.

Thanks for the interesting read and I'll keep an eye on your repo!

Re: Building the worlds jankiest serial to USB cable from scavenged parts

#26

Post by magnat »

ajsnigrutin wrote: post #22
alias_neo wrote: post #4

I'm not sure why I expected more, but I was a little disappointed. Soldering some wires onto an FTDI chip in a pinch is great, but the chip is doing all of the work really. I was hoping to learn I could make a serial to USB with _less than_ an FTDI chip. That said, respect for the effort of taking the photos and writing it up, and it was worth a read to learn about those naughty Scots bricking peoples devices with ba…

USB is hard... you need a chip to deal with it. "Back in my day", you could bitbang stuff with a parallel port, but those days are gone. I would've picked a more lazy approach, just pull the atmega chip from an arduino (to not cause issues), and use the rx and tx pins on the (now empty) arduino board, since they're both connected to ftdi chip already, and no de/soldering is needed.

You can actually bit-bang low speed USB on Arduino [0]. There is even a bootloader [1] for ATtiny visible to host as HID USB device. It is obviously not compatible with Arduino, but those tiny boards look too cute to ignore [2]. Also, you can use USB port both for downloading firmware and your application.

[0] https://github.com/obdev/v-usb

[1] https://github.com/micronucleus/micronucleus

[2] https://cpldcpu.wordpress.com/2014/04/25/the-nanite-85/

Re: Building the worlds jankiest serial to USB cable from scavenged parts

#27

Post by f1shy »

unwind wrote: post #7

I thought this was a fun journey through a tiny DIY tooling project, and I enjoyed it! I liked the detail level which is turned up quite high, taking care to explain many of the steps that are (typically) taken for granted by electronics hobbyists. Still, this part stuck with me so I feel a need to comment: The high level overview is that "serial", or UART (Universal Asynchronous Receive and Transmit) is a protocol f…

Actually synchronous in this context has nothing to do with clock. It refers to the fact that the data does not come at regular intervals (synchronous), but asynchronously.

Re: Building the worlds jankiest serial to USB cable from scavenged parts

#28

Post by stereo »

MarkusWandel wrote: post #23

No need to junk a perfectly good Arduino for that. Just load a trivial sketch that disables the Arduino's TX pin and just access the serial link through the D0 (RX0) and D1 (TX0) pins. Reversed of course; what's RX to the Arduino is TX to the serial chip.

My go-to serial adapter is an esp8266 dev board with EN connected to GND to stop the chip itself from booting. The TX and RX pins are then conveniently printed on the board - I just have to remember that, in this case, TX goes to TX and RX to RX, because it shows what's usually the chip's side of the dialog.

Re: Building the worlds jankiest serial to USB cable from scavenged parts

#29

Post by krallja »

Razengan wrote: post #18

Something I'm sure every tech person has mused about now and then: In the case of an apocalypse or cataclysm, how much of our current digital data would we be able to scavenge?

My favorite "arduino-apocalypse" is CollapseOS: https://hn.algolia.com/?query=collapseos

Re: Building the worlds jankiest serial to USB cable from scavenged parts

#30

Post by argulane »

MarkusWandel wrote: post #23

No need to junk a perfectly good Arduino for that. Just load a trivial sketch that disables the Arduino's TX pin and just access the serial link through the D0 (RX0) and D1 (TX0) pins. Reversed of course; what's RX to the Arduino is TX to the serial chip.

You don't even have to load a sketch to the Arduino. Just connect the RESET pin to GND. That will keep the Atmega IC on stop state and the TX/RX pins are free for what ever you need them to use for.
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