6 ms·

lcamtuf, or as I like to call him "imposter syndrome as a service" (that's not totally fair; I've caught up to him in many ways over the past few years). Now t

by dekhn 3y ago

lcamtuf, or as I like to call him "imposter syndrome as a service" (that's not totally fair; I've caught up to him in many ways over the past few years). Now that I know what a relay is, I can't unhear it. When I plug in my EV for charging, I hear the solid click of a (probably quite large) relay. When my coffee maker cycles on or off, I hear a relay. I don't particularly like it.

082349872349872 3y ago
When I was small, my parents got me a Fischertechnik kit that included relays. I still remember the day I discovered that by hooking the output of a relay to its input, one could either produce stable or instable (cf the Y combinator?) behaviour, and the latter produced a relay clicking like mad, as fast as its time constants allowed it...
- jacquesm 3y ago
  Bonus points for mechanically tuning the relay to give you the highest frequency possible. A little screw set into the top of the relay casing that pushes down on the arm can make the relay substantially quicker (at the price of some more contact bounce but that's fine).
  - eichin 3y ago
    Oooh, flashback to early TRS-80 days - there was an on-motherboard relay to control the tapedeck (pause/continue transport, you still had to have the buttons pushed down.) You could instead drive it fast enough to make (very grating) tones, probably damaging it over time (your limiting factor was "everyone in earshot trying to make you stop", by "grating" I mean "small metal box full of bees" :-)
    - actionfromafar 3y ago
      MSX had the same thing. I played with it a bit but worried I might break it :-)
frabert 3y ago
What you're hearing when your coffee maker cycles on and off may actually be a bimetallic strip used as temperature control so technically not a relay
- byhemechi 3y ago
  Bimetallic strips are pretty slow, I can't imagine them being audible. I'd guess what you're hearing is almost certainly a relay, very likely driven by the bimetallic strip edit: Replies have pointed out that they sometimes do "snap", so i guess i'm wrong there. I'm still pretty sure anything in a kettle/coffee pot/toaster etc would be a relay to avoid arcing edit 2: i'm just going to shut up now
  - frabert 3y ago
    It's totally possible to shape a bimetallic strip in a way that makes it bistable, thus clicking between the two states, just like an electrical switch which uses springs inside which are normally not noisy either.
    - HeyLaughingBoy 3y ago
      This is actually the only type that I've ever seen.
      - bagels 3y ago
        They used to use a coiled strip with a mercury switch on the end of it.
        HeyLaughingBoy 3y ago
        Right!!! In the old thermostats. I forgot about those.
    - aidenn0 3y ago
      One construction I've seen is with a permanent magnet for hysteresis; the strip jumps to the magnet when it gets close, and then requires extra tension to release. The thermostat in my first apartment worked this way (and it looked to me like the strip was actually carrying the current to operate the gas heater; presumably a NC valve).
bqmjjx0kac 3y ago
I follow lcamtuf on Mastodon and I am convinced he's made of different stuff than I am. A full-time job is enough for me, I can't imagine starting (and completing) so many cool side projects. To that point, right before this relay madness, he wrote up an article in a playable embedded Tetris clone: <https://lcamtuf.substack.com/p/mcu-land-part-10-blocks-all-the-way https://lcamtuf.substack.com/p/mcu-land-part-10-blocks-all-t...>.
- dragontamer 3y ago
  That PCB mildly triggers me for some reason. No small 100nF capacitors. Only a bulk 1uF and 10uF capacitor inches away. Very inefficient layout. Is that just a 10 Ohm resistor connected to a physical switch to control the backlight? DC-DC module? He's got a PCB on there already, it shouldn't be that much harder to slap down a Buck converter himself. What size components are those? Far larger than 0805, they might actually be like 2012 (inch) components. Good grief. I guess Microchip / Atmel chips are legendary for this reason: they always were considered braindead easy to boot. But this is the higher-end Cortex-M7 series chips, I'd imagine that you'd need at least a _bit_ more care with regards to decoupling and power-delivery to achieve reliability than what he did here! No seriously. A 300MHz processor with _NO_ local decoupling capacitors? Is he mad? ------------ But then again, I guess there's something to be said about making a board "easier" and through less effort. I guess there's no reason to be a masochist with 0603 (or smaller) parts when prototyping.
  - dekhn 3y ago
    He explains all his decisions for PCB design (https://lcamtuf.substack.com/p/designing-your-own-pcbs https://lcamtuf.substack.com/p/designing-your-own-pcbs) and note this is a small-run device mainly intended for pedagogical reasons. Also the device worked even when it was on a breadboard, suggesting he made reasonable technical decisions regarding placebo capacitors.
    - dragontamer 3y ago
      AVR DB is a 24MHz computer though. This other post (https://lcamtuf.substack.com/p/mcu-land-part-3-baby-steps-with-cortex https://lcamtuf.substack.com/p/mcu-land-part-3-baby-steps-wi...) has more information with his experiments with SAMS70, suggesting experimentation with a breakout board. So same same overall but... He's upgraded to the SAMS70 which is 300MHz. Its a totally different class of processor. > Also the device worked even when it was on a breadboard, suggesting he made reasonable technical decisions regarding placebo capacitors. I dunno. PDN (power-delivery network) issues are really complex. You solve a lot of headaches with a 1-penny 100nF capacitor here and there. I'm very curious what the SAMS70's onboard capacitance is. I'm wondering if Microchip/Atmel goes overboard on onboard capacitance or something. In any case: the documentation from Microchip is clear about this. 100nF capacitors on every input pin. I don't see any reason to stray from this, its not like 100nF capacitors are expensive, or even difficult to solder.
Pathogen-David 3y ago
In an EV charger, it's more likely to be a contactor, which is similar to a relay but can better deal with high amounts of current. (Technology Connections has a video on the differences https://youtu.be/VsNHrAzx5_w https://youtu.be/VsNHrAzx5_w) If you want more household relays to notice, it's common to find them in digital thermostats for central HVAC control signaling. I've also found them inside of ovens, and cars also have lots of them for things like the starter and headlights (although maybe not the latter in newer cars.)
- dekhn 3y ago
  I hadn't heard of contactor but that looks like it's just a subtype of relay? And I notice that it says contactors are used where relays start to top out, around 15A. Which is interesting because the max current I can configure my RAV4 Prime to is ... 14A. Either way I'm not opening up the little portable box that makes this noise. It's clear there's something physical clacking in there, not solid state.
  - HeyLaughingBoy 3y ago
    Yes, the big deal with contactors is that they're designed to switch high-current inductive loads. Smaller relays may have problems with the arcing caused by a load like a motor welding the contacts together. So, they have bigger contacts to handle the current and strong springs and a powerful solenoid to open/close the contacts quickly and extinguish an arc before it has time to melt anything. The noise you're hearing is from the contacts opening and closing.
- throttlebody 3y ago
  Relays and contractors are the same. It's a coil physically movin some contacts together to allow current to flow. I got no idea why, where or how the naming came about or who decides. But i guess its the same as creeks and rivers, when does a creek become a river
  - userbinator 3y ago
    The term contactor came from industrial machinery, while relay came from telecoms.

by dekhn 3y ago

082349872349872 3y ago

When I was small, my parents got me a Fischertechnik kit that included relays. I still remember the day I discovered that by hooking the output of a relay to its input, one could either produce stable or instable (cf the Y combinator?) behaviour, and the latter produced a relay clicking like mad, as fast as its time constants allowed it...

jacquesm 3y ago
Bonus points for mechanically tuning the relay to give you the highest frequency possible. A little screw set into the top of the relay casing that pushes down on the arm can make the relay substantially quicker (at the price of some more contact bounce but that's fine).
- eichin 3y ago
  Oooh, flashback to early TRS-80 days - there was an on-motherboard relay to control the tapedeck (pause/continue transport, you still had to have the buttons pushed down.) You could instead drive it fast enough to make (very grating) tones, probably damaging it over time (your limiting factor was "everyone in earshot trying to make you stop", by "grating" I mean "small metal box full of bees" :-)
  - actionfromafar 3y ago
    MSX had the same thing. I played with it a bit but worried I might break it :-)

frabert 3y ago

What you're hearing when your coffee maker cycles on and off may actually be a bimetallic strip used as temperature control so technically not a relay

byhemechi 3y ago
Bimetallic strips are pretty slow, I can't imagine them being audible. I'd guess what you're hearing is almost certainly a relay, very likely driven by the bimetallic strip edit: Replies have pointed out that they sometimes do "snap", so i guess i'm wrong there. I'm still pretty sure anything in a kettle/coffee pot/toaster etc would be a relay to avoid arcing edit 2: i'm just going to shut up now
- frabert 3y ago
  It's totally possible to shape a bimetallic strip in a way that makes it bistable, thus clicking between the two states, just like an electrical switch which uses springs inside which are normally not noisy either.
  - HeyLaughingBoy 3y ago
    This is actually the only type that I've ever seen.
    - bagels 3y ago
      They used to use a coiled strip with a mercury switch on the end of it.
      - HeyLaughingBoy 3y ago
        Right!!! In the old thermostats. I forgot about those.
  - aidenn0 3y ago
    One construction I've seen is with a permanent magnet for hysteresis; the strip jumps to the magnet when it gets close, and then requires extra tension to release. The thermostat in my first apartment worked this way (and it looked to me like the strip was actually carrying the current to operate the gas heater; presumably a NC valve).

bqmjjx0kac 3y ago

I follow lcamtuf on Mastodon and I am convinced he's made of different stuff than I am. A full-time job is enough for me, I can't imagine starting (and completing) so many cool side projects. To that point, right before this relay madness, he wrote up an article in a playable embedded Tetris clone: <https://lcamtuf.substack.com/p/mcu-land-part-10-blocks-all-the-way https://lcamtuf.substack.com/p/mcu-land-part-10-blocks-all-t...>.

dragontamer 3y ago
That PCB mildly triggers me for some reason. No small 100nF capacitors. Only a bulk 1uF and 10uF capacitor inches away. Very inefficient layout. Is that just a 10 Ohm resistor connected to a physical switch to control the backlight? DC-DC module? He's got a PCB on there already, it shouldn't be that much harder to slap down a Buck converter himself. What size components are those? Far larger than 0805, they might actually be like 2012 (inch) components. Good grief. I guess Microchip / Atmel chips are legendary for this reason: they always were considered braindead easy to boot. But this is the higher-end Cortex-M7 series chips, I'd imagine that you'd need at least a _bit_ more care with regards to decoupling and power-delivery to achieve reliability than what he did here! No seriously. A 300MHz processor with _NO_ local decoupling capacitors? Is he mad? ------------ But then again, I guess there's something to be said about making a board "easier" and through less effort. I guess there's no reason to be a masochist with 0603 (or smaller) parts when prototyping.
- dekhn 3y ago
  He explains all his decisions for PCB design (https://lcamtuf.substack.com/p/designing-your-own-pcbs https://lcamtuf.substack.com/p/designing-your-own-pcbs) and note this is a small-run device mainly intended for pedagogical reasons. Also the device worked even when it was on a breadboard, suggesting he made reasonable technical decisions regarding placebo capacitors.
  - dragontamer 3y ago
    AVR DB is a 24MHz computer though. This other post (https://lcamtuf.substack.com/p/mcu-land-part-3-baby-steps-with-cortex https://lcamtuf.substack.com/p/mcu-land-part-3-baby-steps-wi...) has more information with his experiments with SAMS70, suggesting experimentation with a breakout board. So same same overall but... He's upgraded to the SAMS70 which is 300MHz. Its a totally different class of processor. > Also the device worked even when it was on a breadboard, suggesting he made reasonable technical decisions regarding placebo capacitors. I dunno. PDN (power-delivery network) issues are really complex. You solve a lot of headaches with a 1-penny 100nF capacitor here and there. I'm very curious what the SAMS70's onboard capacitance is. I'm wondering if Microchip/Atmel goes overboard on onboard capacitance or something. In any case: the documentation from Microchip is clear about this. 100nF capacitors on every input pin. I don't see any reason to stray from this, its not like 100nF capacitors are expensive, or even difficult to solder.

Pathogen-David 3y ago

In an EV charger, it's more likely to be a contactor, which is similar to a relay but can better deal with high amounts of current. (Technology Connections has a video on the differences https://youtu.be/VsNHrAzx5_w https://youtu.be/VsNHrAzx5_w) If you want more household relays to notice, it's common to find them in digital thermostats for central HVAC control signaling. I've also found them inside of ovens, and cars also have lots of them for things like the starter and headlights (although maybe not the latter in newer cars.)

dekhn 3y ago
I hadn't heard of contactor but that looks like it's just a subtype of relay? And I notice that it says contactors are used where relays start to top out, around 15A. Which is interesting because the max current I can configure my RAV4 Prime to is ... 14A. Either way I'm not opening up the little portable box that makes this noise. It's clear there's something physical clacking in there, not solid state.
- HeyLaughingBoy 3y ago
  Yes, the big deal with contactors is that they're designed to switch high-current inductive loads. Smaller relays may have problems with the arcing caused by a load like a motor welding the contacts together. So, they have bigger contacts to handle the current and strong springs and a powerful solenoid to open/close the contacts quickly and extinguish an arc before it has time to melt anything. The noise you're hearing is from the contacts opening and closing.
throttlebody 3y ago
Relays and contractors are the same. It's a coil physically movin some contacts together to allow current to flow. I got no idea why, where or how the naming came about or who decides. But i guess its the same as creeks and rivers, when does a creek become a river
- userbinator 3y ago
  The term contactor came from industrial machinery, while relay came from telecoms.