4 ms·

> i want to use 3.5mm jacks for super simple data communications and power That sounds like an all around bad idea.

by geon 3y ago

icegreentea2 3y ago
It's not the best idea, but it's not the worst idea either. The original Stripe reader used the 3.5mm jack for example. It's even been used in some power applications (https://www.amazon.ca/UY-CHAN-Original-Soldering-Replacement/dp/B07KCKXJQZ?th=1 https://www.amazon.ca/UY-CHAN-Original-Soldering-Replacement...)
- krallja 3y ago
  Square*
- kragen 3y ago
  i haven't tested this, but i think it is a less bad idea for what i want to use it for, which is 5-volt power at up to 500 milliwatts, than for the ts80 tip. if the ts80 tip is 4.5Ω it needs to carry 3.8 amps, which means 17 volts, which would definitely kill your earphones. but you could imagine that the ts80 uses foldback current limiting or some more elaborate scheme to handle short circuits, which will happen in any case during hotplugging due to the shape of the 3.5mm plug. foldback wouldn't help (the earspeakers are higher resistance than the soldering tip, not lower) but you could design the iron to only turn on the 17 volts if 100 millivolts delivers 20 milliamps or more, say and, yeah, square. i want to do higher data rates and simpler electronics than an actual audio interface can handle, though
kragen 3y ago
it's like a ratburger: it's not good, but hey, it sure is cheap
ahdsr 3y ago
ZSA uses this for their keyboards. The moonlander I'm typing this on uses a headphone jack for all of the above [1] [1] https://www.zsa.io/moonlander/ https://www.zsa.io/moonlander/
- kragen 3y ago
  this is pretty cool
em3rgent0rdr 3y ago
Apple's iPod Shuffle 2G did charging and USB syncing over its 3.5mm TRRS socket. And for people concerned about accidentally shorting a power line when inserting the plug, hypothetically could use a socket with built in switches so power is only sent once the plug is fully inserted into the socket.
- kragen 3y ago
  oh hey, that's a pretty good idea, thanks! you can tell i'm a novice it would still probably burn out my earbuds if i put 5 volts at 100 milliamps on the tip connector once the plug was fully inserted
  - em3rgent0rdr 3y ago
    oh ok, I understand your concern now "how do i keep from burning out headphones if someone accidentally plugs them in". I am hesitant to give advice because I don't know a great way, but a possible method of detecting what type of device (a headphone or USB device) is plugged in could work by doing an impedance measurement right after the device is inserted. USB standard specifies that the signal-to-ground impedance on the data lines is 30 ohms and between data lines is differential impedance of 90 ohms. The right and left channel of headphones meanwhile have an impedance to ground (from 4 ohms to 32 ohms or higher), but aren't set to a differential impedance between the left and right channel. So maybe there is a simple circuit that could measure the differential impedance that is triggered just after a device is inserted, and if it matches 90 ohms, then will treat the device as a USB device, but if a measurement matches a headphone, then treat the device as a headphone. But the specifics on how to do this, I'm not sure.
    - em3rgent0rdr 3y ago
      Also see figure 3 of https://www.onsemi.com/pub/collateral/and8074-d.pdf https://www.onsemi.com/pub/collateral/and8074-d.pdf which gives a schematic of USB lines and says "if a 1.5 k pull up resistor is connected on either the D+ or D− line, the port is identified as upstream". Unfortunately downstream devices have pull-down to ground, so when not being driven would rest at low voltage, which I can't think of a great way to help to distinguish downstream USB from headphones.

> i want to use 3.5mm jacks for super simple data communications and power That sounds like an all around bad idea.

by geon 3y ago

> i want to use 3.5mm jacks for super simple data communications and power That sounds like an all around bad idea.

It's not the best idea, but it's not the worst idea either. The original Stripe reader used the 3.5mm jack for example. It's even been used in some power applications (https://www.amazon.ca/UY-CHAN-Original-Soldering-Replacement/dp/B07KCKXJQZ?th=1 https://www.amazon.ca/UY-CHAN-Original-Soldering-Replacement...)

krallja 3y ago
Square*
kragen 3y ago
i haven't tested this, but i think it is a less bad idea for what i want to use it for, which is 5-volt power at up to 500 milliwatts, than for the ts80 tip. if the ts80 tip is 4.5Ω it needs to carry 3.8 amps, which means 17 volts, which would definitely kill your earphones. but you could imagine that the ts80 uses foldback current limiting or some more elaborate scheme to handle short circuits, which will happen in any case during hotplugging due to the shape of the 3.5mm plug. foldback wouldn't help (the earspeakers are higher resistance than the soldering tip, not lower) but you could design the iron to only turn on the 17 volts if 100 millivolts delivers 20 milliamps or more, say and, yeah, square. i want to do higher data rates and simpler electronics than an actual audio interface can handle, though

kragen 3y ago

it's like a ratburger: it's not good, but hey, it sure is cheap

ahdsr 3y ago

ZSA uses this for their keyboards. The moonlander I'm typing this on uses a headphone jack for all of the above [1] [1] https://www.zsa.io/moonlander/ https://www.zsa.io/moonlander/

kragen 3y ago
this is pretty cool

em3rgent0rdr 3y ago

Apple's iPod Shuffle 2G did charging and USB syncing over its 3.5mm TRRS socket. And for people concerned about accidentally shorting a power line when inserting the plug, hypothetically could use a socket with built in switches so power is only sent once the plug is fully inserted into the socket.

kragen 3y ago
oh hey, that's a pretty good idea, thanks! you can tell i'm a novice it would still probably burn out my earbuds if i put 5 volts at 100 milliamps on the tip connector once the plug was fully inserted
- em3rgent0rdr 3y ago
  oh ok, I understand your concern now "how do i keep from burning out headphones if someone accidentally plugs them in". I am hesitant to give advice because I don't know a great way, but a possible method of detecting what type of device (a headphone or USB device) is plugged in could work by doing an impedance measurement right after the device is inserted. USB standard specifies that the signal-to-ground impedance on the data lines is 30 ohms and between data lines is differential impedance of 90 ohms. The right and left channel of headphones meanwhile have an impedance to ground (from 4 ohms to 32 ohms or higher), but aren't set to a differential impedance between the left and right channel. So maybe there is a simple circuit that could measure the differential impedance that is triggered just after a device is inserted, and if it matches 90 ohms, then will treat the device as a USB device, but if a measurement matches a headphone, then treat the device as a headphone. But the specifics on how to do this, I'm not sure.
  - em3rgent0rdr 3y ago
    Also see figure 3 of https://www.onsemi.com/pub/collateral/and8074-d.pdf https://www.onsemi.com/pub/collateral/and8074-d.pdf which gives a schematic of USB lines and says "if a 1.5 k pull up resistor is connected on either the D+ or D− line, the port is identified as upstream". Unfortunately downstream devices have pull-down to ground, so when not being driven would rest at low voltage, which I can't think of a great way to help to distinguish downstream USB from headphones.