PCB Metro Map | Hacker News Reader

PCB Metro Map

chaijiaxun.com

124 pointszdw19 comments

In Paris, we used to have special boards at big stations: a map of the subway system, and a button board with one button per station in the city; if you pressed a button, the path would light on the map explaining how to reach it:

https://spacefiction.files.wordpress.com/2017/11/indicateur_...

Those appeared in 1937, so they're very old tech; it would be fun to have a pocket version.

They've since disappeared and been replaced by touch screens, but those are just not the same.

https://spacefiction.fr/2017/11/06/patrick-modiano-et-la-mem...

> The Bay Area Map was actually the simplest one to do since the train system is so sparse. I honestly am not terribly excited about the train system here, but since I do live in the Bay Area, I felt like I should do it for completion’s sake.

sigh

Same, and I live in the Bay too

Instead of attaching transistors to shift registers there are shift register with open drain outputs and led drivers with shift register like interface designed for usecase like this. Some of them even have constant current drivers builtin which would allow eliminating the resistors further simplifying the build although that might require higher supply voltages for longer LED chains which might not be ideal for this project.

Attiny85 operates at the same <20Mhz as ATMega328 in arduino pro mini lack so first one being too slow shouldn't be a thing. From the screenshots it seems that output enable pin wasn't used so I assume fading was done by quickly changing picture. A better approach would be connecting the output enable pin of shift registers to hardware PWM output of microcontroller that way fading can be controlled independently from picture content and easily run frequency where flickering isn't visible even for camera. You wouldn't try to dim a monitor by rapidly changing the picture, same situation with LEDs.

Expanding on this, for applications like this charlieplexing led drivers like the IS31FL3731 can make the layout even easier. They require fewer PCB traces and have built in individual PWM control. One chip can drive up to 144 LEDs, so even for the large maps 2 chips would be enough.

Pulling back soldermask is a useful trick to know if anyone's trying to do something like this themselves. It's another bit to play with: twice the number of visually distinct areas! And if you're willing to pay for multilayer boards, having different copper structures on layer 2 and (N-1) can create really interesting lighting effects.

And never use JLCpcb if you care about quality silk.

Still, nice project!

JLC "have" multiple factories, ie. they outsource board production to one of a number of third parties. You are mostly exposed to this with boards that do not have SMT components, since AFAIK SMT will automatically route your PCB to the SMT-capable PCBA (one factory only).

I am really nonplussed with them recently for a number of reasons and have begun to reach out to PCBAs here in China independently. As I would prefer to have a decent frontend for handing off work (quote, pay, support, etc.) I hacked one together last night. Let me know here if anyone else would like such a service. Ideally you pick your own PCBA and both parties communicate via the platform. Conceptually reputation should accrue with volume, with turnaround times and quality issues recorded publicly.

Wow, those look really nice!

Reminds me of this project which I stumbled across recently: https://www.traintrackr.io/

Irish trains used to have LED maps on the trains themselves, showing position. Though they only showed the relevant line, so were a lot less intricate than this.

They were also often just wrong; fun as they were it's probably just as well that they got rid of them.

Also there are very few lines with very few intersections. You will have to change train at Limerick Junction though.

The Dublin commuter network's probably about as complex as the Bay Area one shown in the article, but the LED maps never showed the whole thing, only the specific line.

Did the author consider bottom firing LEDs? (https://www.kingbrightusa.com/category.asp?catalog_name=LED&...) - they are like SMD LEDs, but the light comes out the bottom - the footprint needs to include a hole between the pads for the light to come through. Seems like a good solution for this problem.

You can also use buried components, which are sandwiched between layers inside the PCB. This of course requires a thick PCB and is really expensive. Though it would be quite nice for an art piece I suppose, zero exposed circuitry, everything buried. You could achieve a similar effect for this particular project by just ordering ~four PCBs with the necessary cutouts and gluing them together yourself, as connectivity between the PCBs isn't really required.

Mounting the LEDs on the back can work quite well if you have some kind of reasonably reflective surface on the back. You don’t even need a hole in the PCB, just a gap in all of the copper layers. I used this approach in my light meter project: https://github.com/addrummond/mlm In this case the reflector is just plastic painted with gloss white.

Also, awesome project!

A super cool next step would be to track the actual trains with the LEDs, is there any city with an open API for that?

And the next step: hover your mouse over a train and see information such as speed, whether it is on schedule, etc.

Boston’s MBTA has an API, and sells a live-updating PCB train tracker: https://www.mbtagifts.com/products/mbta-dual-direction-train...

Not sure where Matthew gets the data from, but he’s got a page with live London tube train positioning (updated today with the two new Northern Line stations): https://traintimes.org.uk/map/tube/

I don’t have anything to add, but this is pretty cool!

Pretty cool. I admire your perseverance on it.

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