sacred lodge
*WIP* needs cleanup
Signal on lfrfid antenna at 77.5kHz is barely there, but significantly stronger (and picked up by my watch from more than a few mms away) on second harmonic.
Clock signal is generated from FZ internal clock.
Baseband signal also comes out through GPIO for those special times you need a portable DCF77 TXer and have a portable LF antenna array in your pocket. Building said TXer is left as an exercise for the reader.
topaz bronze
Is this for setting those watches and clocks through rf? Great work!
lime schooner
Too bad I don't still own a US radio clock, I wonder if 60khz for the USA WWVB station signal would be too low to get any kind reasonable output.
loud flare
where is the source?
umbral delta
Would love to see the source + get any pointers you have or references you used for the RFID HAL API! I’ve been trying to write my own app that uses the LF coil (similar to this) but have been struggling
loud flare
@sacred lodge ping
sacred lodge
bong
no source yet cause it s a mess
rfid hal api is no api for what i did, you simply set a timer and bitbang a pin. you can find more in the rfid reader app
lfrfid works entirely bitbanged in software, with the hardware simply being a gain stage for output, and a bunch of filters on the input
umbral delta
@sacred lodge how does the timer system work? I was looking at doing it naively with furi_delay_us() and loops, but skotopes#4130 mentioned I’d run into issues without disabling interrupts &c.
Also, when you say bitbanging, you mean just furi_hal_gpio_write()-ing to RFID_OUT? Anything else you had to do to get it to work beyond init-ing that pin?
glacial vale
@sacred lodge tried it with my DCF77 clock; no luck (yet) on what GPIO pin is the signal also available? will try again with a wire loop
used it with FW 0.71.2 , is that the correct API ?
sacred lodge
<@704692057867944009> how does the timer system work? I was looking at doing it ...
flipper is running an OS, you only get to use one app, but there's other stuff in the background, like lcd refresh or i/o to the lfrfid pin
bare metal, a timer simply stops execution and jumps to a specific piece of code (interrupt vector). in freertos and flipper, timers are a bit more involved, you schedule stuff to happen at specific intervalz
sacred lodge
Also, when you say bitbanging, you mean just furi_hal_gpio_write()-ing to RFID_O...
not really, no, i just set the timer to interrupt at twice my desired frequency to generate a carrier, and disable/enable it to match the signal
sacred lodge
<@704692057867944009> tried it with my DCF77 clock; no luck (yet) on what GPIO p...
the range is abysmal, i got a few centimeters at best. the antenna is severely mistuned at that freq. two clocks works for me, one doesn't - i suspect there's an encoding error somewhere
umbral delta
not really, no, i just set the timer to interrupt at twice my desired frequency ...
Appreciate the quick explainer. Any good spots to educate myself on timer usage then? The LFRFID source code is a bit obfuscated for me with the layers of workers / threads / error handling they’ve got in there
sacred lodge
iirc it was the leftmost pin, it should blink in sync with the FZ led. but it's only the baseband signal (1Hz and 80%/90% duty cycle for 0/1)
uh
sacred lodge
Appreciate the quick explainer. Any good spots to educate myself on timer usage ...
i'd honestly start with a simpler architecture, like avr or pic18
try to go bare metal and see what registers do and what happens
stm32 is quite a lot to take in as a first dive into embedded but... if you'd rather not do that
probably reading on freertos timers and threds and checking how flipper implements them will suffice for your application
the thing is, you really need to go deeper and understand the hardware
for example in my case (77.5khz rf signal, 1Hz baseband signal) you can bitbang and run a timer at 155 khz... or you can simply figure out how to tell the hardware to generate a 155khz signal for you, which you can enable or disable
umbral delta
stm32 is quite a lot to take in as a first dive into embedded but... if you'd ra...
Yeah, it’s definitely been drinking from the firehose; I’m a weird mix of pure math and MechE so this is all new territory to me
umbral delta
for example in my case (77.5khz rf signal, 1Hz baseband signal) you can bitbang ...
So the former is what you did here, right? How would the latter work?
sacred lodge
no, i did the latter
set timer registers to generate a 155khz signal, which i conveniently disable/enable to match dcf77 specs
you can check hardware "code" in the furi_hal_* files and check how those functions are used in stock applications
you can literally do it all on github too, it's got great search and crossreferencing, unlike some "modern" electronjs IDEs
guess bitbangijg it was a misnomer on my side
it was meant like "flipper does lfrfid with its gpio, no extra ICs"
glacial vale
the range is abysmal, i got a few centimeters at best. the antenna is severely m...
maybe this is the reason some work and others don't; there is a signal injection on the roll over from end to start over
sacred lodge
i don't understand what that means
the 59th second is marked different than 0 or 1 bits, otherwise, you wouldn't know when is the :00 second
glacial vale
this is the signal from FZ pinA7
glacial vale
on the GPIO side A7
all bits are banged clean
only the last sequence is disturbed
sacred lodge
yeah that shouldn't happen byt i never tested with a TXer from gpio, only with the rfid antenna
glacial vale
(stupid) idea to inject a time out at start/end to avoid /idenfy the cause?
sacred lodge
it probably filtered it out
will check
nah i know 100% what it is, it's what generates the special 59 seconds bit
glacial vale
what should be the freq? That I can verify
glacial vale
happens after -end bit-
sacred lodge
however, the 59th bit is a full 1000ms carrier on/0ms off
59th bit + 0th bit are usually a long, almost 2 sec mark
glacial vale
Ok will focus on that and report back
glacial vale
Build? nearby wire loop not enough?
sacred lodge
oh i don't mean anything on the scale of the Mainhausen installation 🙃
glacial vale
going for the easy/lazy way
what I can see = last bit is not cleared and first bit is mashed up , a small delay might solve it
glacial vale
you planning to build a TXer too?
using the FZ for this is a PLUS
glacial vale
59th bit + 0th bit are usually a long, almost 2 sec mark
no 2 sec mark found, only 1 sec
sacred lodge
i'm not using a delay, i'm syncing to FZ's clock and enabling the 77.5 carrier on, iirc, a 10 Hz timer (so i can create duty cycles in 10% steps)
pfobably just some logic messed up on the end condition
will check when i get home
glacial vale
Thanks!
sacred lodge
yeah, using the internal antenna is definitely the appeal here i agree
otherwise it would just be yet another arduino-clone-board project
glacial vale
use the onboard antenna (stealth mode) out of the box (thinking)
on the other hand: GPIO output gave a insight on the generated signal (debug)
glacial vale
@sacred lodge found some solution/strange code?
sacred lodge
sorry, didn't follow through
new kernel brought a lot of changes since 0.68 and even after compiling making the old app compile, it still randomly crashes on the new kernel
going back to 0.68, same code works fine, so I'm not sure what I'm doing wrong
will check
glacial vale
Thank you!
sacred lodge
compiled against 0.74.2, had a few changes
gpio out is C3 now near gnd, A7 was the comparator output
it's... sketchier though. i'm not sure what changed over in three releases, but the timer which generates the baseband signal is somehow even less stable now
(was 30 Hz, with 24/30 or 27/30 full carrier on - to generate 800, respectively 900 ms pulses)
gonna try with 10Hz lol, i should probably move away from a furi timer and use a rtos native one
it seems to stabilize after one cycle though
it seems to happen on a very dumb program too (interrupt at 30 hz, pin on for 15 cycles, off for 15 cycles) with jitter actually visible on a scope
it does not seem to happe non 0.69 so... idk
technically it works - just not the first try. it even set a watch that the previous ver didnt'
glacial vale
@sacred lodge downloaded and tested: not a (big) success = 1 clock only did catch-up with the minutes and seconds (not hour)
sacred lodge
sadly i doubt you'll get more range out of it, the antenna is really mistuned
even with a real DCF77 signal, it still takes a few minutes for everything to sync up, some smart devices will hold on to values they know they are correct, and compare them with the next values - untill every value is RXed and correctly predicted - some will simply overwrite them and display them. you can even have cheap clocks show 24:69
basically: one timestamp is sent per minute (end of minute = syncs to seconds 00)
if something is missing, you need to wait another minute
I needed about 5 minutes at least for a full sync (even with test dates, not real dates)
there's probably yet another version to abuse the hardware
using the piezo buzzer at 15.5khz
I think it was done like that over headphones
or maybe 7.75 khz, but that's audio range and annoying as hell
oh yeah baby, 7750 hz in audio range, buzzing every second, for a few minutes is going to be ear candy
the dates will probably fail much more often, because the parity is counted over 3 bytes, so if a single bit flips, the whole date fails
I need to learn how to do flipper-style menus and scenes, so I can implement some more tools and settings into this app
umbral delta
oh yeah baby, 7750 hz in audio range, buzzing every second, for a few minutes is...
Folks used the speakers’ parasitic EMF for a 7.8kHz shopping cart wheel lock/unlock signal
See https://www.begaydocrime.com/ for the files and linked defcon talk explaining
Can confirm it works on the flipper as well, you just have to hold it extremely close
sacred lodge
i mean
does the EMF from a voicecoil bouncing against a magnet really count as parasitic? 
the cool thing with audiofreq signals (and harmonics) is that you can do them with anything, phone, smart fridge, old timey mp3 player, reel tape player
so if dcf77 clocks really pick up on 7750hz voicecoil emf when they're tuned to 77500hz, that's cool
i've seen it working with 15500 hz and headphones, but it's so annoying
umbral delta
does the EMF from a voicecoil bouncing against a magnet really count as parasiti...
Lol fair
oblique seal
this is incredible!
thought about it, but dismissed it because i thought the rfid hardware couldnt be "misused" in this way.
sacred lodge
less of a mess 🤷 don't bypass locks and do stuff inside timers like I do; tl:dr don't use my code as reference
half jay
Good morning. For several weeks, it is no longer possible for me to read any RFID badge (although this worked before with these same badges). The emulator works. Any ideas? I have already formatted.