Monophasic waveforms are generally considered less safe than biphasic waveforms. That's why many TENS units have an output stage based around a pulse transformer, so they can deliver two pulses, one in each direction, shortly after each other. Leaving this out seems to me to be a false economy when you've gone to all the effort of building the rest of the system.
I saw a CTO put an email send script in a while (true) loop like this and we only stopped dossing one of our investor’s email after our sendgrid bill hit £32k. Funny thing about emails is they get in a proverbial traffic jam all across the internet so no matter how many times the poor guy would clear his inbox more would magically arrive
The two BJTs do limit current to 20mA on all finger outputs. Voltage feedback is also set up to ensure maximum 32V. MCU protection, well just a ferrite bead.
My trusty TENS device has gotten me through a few bouts of whatever it is I have had for the last year (pudendal neuralgia, sciatica, pelvic floor issue, not sure). But it really is a pain in the ass (ha) to apply the sticky electrode pads.
Has anyone ever seen something like a TENS shirt or shorts that has the pads built-in?
I wonder if this is being used irl. Seems like the next thing would be to attach it to a digital scope like the below. Connecting the low latency of digital compute to the durable self-powered biologic actuators of a human seems like a natural evolution.
That final paragraph smells of LLM. I might be becoming a bit too paranoid, but without any pictures or description of how well it works, can't tell if this is real or not.
That is NOT how one uses lithium batteries one foe snot want to go boom. Consider 3.6V as empty. Discharging them down to 3.0 can cause them to go boom when recharged...
Most cell OEMs will specify safe discharge (low threshold) voltage in a datasheet. 2.75V is quite common [1].
That being said, system designer might choose higher cut-off point, since:
1) charge/discharge curve is S-shaped. There is very little energy in that last few millivolts;
2) battery (protection) circuit, and/or battery itself probably have some small leakage current. However minuscule, over months/years on a shelf, even some nano-amps of leakage will add up. If you want device to survive that, you have to factor this in, so that rest cell voltage still stays above safety threshold even after storage.
Also, "Li-ion" is quite a wide category. Don't use arbitrary voltage as a fast rule. Look up datasheet, or characterize actual cell you use. For some[2], disconnecting at 3.6V would mean leaving 50% of capacity unused. For other[3], that would be a reasonable, if somewhat conservative threshold.
3.6V is considered the nominal voltage, certainly not the low end cut off.
3.0V is considered basically the highest voltage. Most chemistries suggest even lower, 2.8, or even 2.5 in some situations assuming you can control the cutoff carefully. Perfectly safe to do so. You only start to have issues when you’re south of 2.5 without a load.
Most advanced battery usages let the cells drop even below that during heavy load.
>3.6V is considered the nominal voltage, certainly not the low end cut off.
This is not right (3.6v certainly is and can be cut off depending on device and battery).
One thing you are not considering is discharge after the cut off. Fuel gauge, protection circuitry, the cut off circuitry and battery itself has some discharge.
So you don’t want to have the cut off being too low because then the battery is permanently dead after not using it for X period of time.
You want to leave some margin there.
Depending on product, battery chemistry and design I have seen cut-off at 3.0-3.6v.
Anyone setting cut-off at 3.6V either is using it in some insanely industrial, ludicrous application where you need to handle cases like multiple years in storage... or doesn't know how to properly design their protection circuitry.
The margin is already there at 3.0V. You can still recharge batteries discharged below 3.0V. It just becomes dicey below ~2.5V.
>Anyone setting cut-off at 3.6V either is using it in some insanely industrial, ludicrous application where you need to handle cases like multiple years in storage... or doesn't know how to properly design their protection circuitry.
It really depends on application, battery size and leakage. In consumer world of electronics for example there’s an often requirement to make sure device turns on after being on a shelf for 1/2 - 2 years.
Then when you do the math it ends up needing to set the limit to 3-3.6v.
>The margin is already there at 3.0V. You can still recharge batteries discharged below 3.0V. It just becomes dicey below ~2.5V.
The margin isn’t big enough for some products. Furthermore some of the more leading edge batteries (in terms of energy density) have higher leakage which requires having more margin.
Monophasic waveforms are generally considered less safe than biphasic waveforms. That's why many TENS units have an output stage based around a pulse transformer, so they can deliver two pulses, one in each direction, shortly after each other. Leaving this out seems to me to be a false economy when you've gone to all the effort of building the rest of the system.
Coming in a V2, semester just started again, so I have a little less time for it. Given that I also have some other projects on the way :)
I saw a CTO put an email send script in a while (true) loop like this and we only stopped dossing one of our investor’s email after our sendgrid bill hit £32k. Funny thing about emails is they get in a proverbial traffic jam all across the internet so no matter how many times the poor guy would clear his inbox more would magically arrive
Did you reply to the wrong thread?
I tried to build some TENS device, but lost in "safety maze".
I reverse engineered some existing device, there are TONS of safety measures.
At least: current limiting resistor, transformer, voltage/current feedback, GND isolation, MCU protection.
After replicate all of these, I still not brave enough to try it myself, I just find it too dangerous.
PS: TENS device is fun. article seems like a bait.
The two BJTs do limit current to 20mA on all finger outputs. Voltage feedback is also set up to ensure maximum 32V. MCU protection, well just a ferrite bead.
My trusty TENS device has gotten me through a few bouts of whatever it is I have had for the last year (pudendal neuralgia, sciatica, pelvic floor issue, not sure). But it really is a pain in the ass (ha) to apply the sticky electrode pads.
Has anyone ever seen something like a TENS shirt or shorts that has the pads built-in?
In my searches, yes, I found something like that from an italian university. Sadly can't find the paper now.
I see
> Each electrode channel is tied to a finger pad
but the layout shows the finger pads are all tied together. What am I missing?
Poor wording, should mean that each finger has a dedicated output, but you are right, they are all tied together
Tangentially related homebrew effort by Basically Homeless to built an aimbot using similar tech.
https://youtube.com/watch?v=9alJwQG-Wbk
I wonder if this is being used irl. Seems like the next thing would be to attach it to a digital scope like the below. Connecting the low latency of digital compute to the durable self-powered biologic actuators of a human seems like a natural evolution.
https://www.youtube.com/watch?v=DCp8-tc0dfY
That final paragraph smells of LLM. I might be becoming a bit too paranoid, but without any pictures or description of how well it works, can't tell if this is real or not.
What do people use this for?
This is cool, and all, but you can buy a TENS unit for $20.00 to $40.00 on Amazon.
> down to ~3.0V (discharged).
That is NOT how one uses lithium batteries one foe snot want to go boom. Consider 3.6V as empty. Discharging them down to 3.0 can cause them to go boom when recharged...
Most cell OEMs will specify safe discharge (low threshold) voltage in a datasheet. 2.75V is quite common [1].
That being said, system designer might choose higher cut-off point, since:
1) charge/discharge curve is S-shaped. There is very little energy in that last few millivolts;
2) battery (protection) circuit, and/or battery itself probably have some small leakage current. However minuscule, over months/years on a shelf, even some nano-amps of leakage will add up. If you want device to survive that, you have to factor this in, so that rest cell voltage still stays above safety threshold even after storage.
Also, "Li-ion" is quite a wide category. Don't use arbitrary voltage as a fast rule. Look up datasheet, or characterize actual cell you use. For some[2], disconnecting at 3.6V would mean leaving 50% of capacity unused. For other[3], that would be a reasonable, if somewhat conservative threshold.
[1] https://docs.rs-online.com/080b/A700000007848112.pdf
[2] https://www.murata.com/-/media/webrenewal/products/batteries...
[3] https://ntrs.nasa.gov/api/citations/20140005830/downloads/20... (page 4)
Of course you can go down there? That's literally the lower limit of design voltage?
Below 2,5V is usually when you don't wanna use them anymore
only if you want them to lose capacity fast and become spicy pillows in your lifetime
2.5V is the absolute minimum typically mentioned in spec sheets, 2.8V and above is perfectly fine.
3.6V is considered the nominal voltage, certainly not the low end cut off.
3.0V is considered basically the highest voltage. Most chemistries suggest even lower, 2.8, or even 2.5 in some situations assuming you can control the cutoff carefully. Perfectly safe to do so. You only start to have issues when you’re south of 2.5 without a load.
Most advanced battery usages let the cells drop even below that during heavy load.
>3.6V is considered the nominal voltage, certainly not the low end cut off.
This is not right (3.6v certainly is and can be cut off depending on device and battery).
One thing you are not considering is discharge after the cut off. Fuel gauge, protection circuitry, the cut off circuitry and battery itself has some discharge.
So you don’t want to have the cut off being too low because then the battery is permanently dead after not using it for X period of time.
You want to leave some margin there.
Depending on product, battery chemistry and design I have seen cut-off at 3.0-3.6v.
Anyone setting cut-off at 3.6V either is using it in some insanely industrial, ludicrous application where you need to handle cases like multiple years in storage... or doesn't know how to properly design their protection circuitry.
The margin is already there at 3.0V. You can still recharge batteries discharged below 3.0V. It just becomes dicey below ~2.5V.
>Anyone setting cut-off at 3.6V either is using it in some insanely industrial, ludicrous application where you need to handle cases like multiple years in storage... or doesn't know how to properly design their protection circuitry.
It really depends on application, battery size and leakage. In consumer world of electronics for example there’s an often requirement to make sure device turns on after being on a shelf for 1/2 - 2 years.
Then when you do the math it ends up needing to set the limit to 3-3.6v.
>The margin is already there at 3.0V. You can still recharge batteries discharged below 3.0V. It just becomes dicey below ~2.5V.
The margin isn’t big enough for some products. Furthermore some of the more leading edge batteries (in terms of energy density) have higher leakage which requires having more margin.
^^ this
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