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.
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.
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
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.
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.
lambdaone|3 months ago
autonomydriver|3 months ago
zhouyisu|3 months ago
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.
autonomydriver|3 months ago
sowbug|3 months ago
Has anyone ever seen something like a TENS shirt or shorts that has the pads built-in?
autonomydriver|3 months ago
clnhlzmn|3 months ago
> Each electrode channel is tied to a finger pad
but the layout shows the finger pads are all tied together. What am I missing?
autonomydriver|3 months ago
cheschire|3 months ago
https://youtube.com/watch?v=9alJwQG-Wbk
adolph|3 months ago
https://www.youtube.com/watch?v=DCp8-tc0dfY
mrcartmeneses|3 months ago
atombender|3 months ago
dmitrygr|3 months ago
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...
kees99|3 months ago
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)
cenamus|3 months ago
Below 2,5V is usually when you don't wanna use them anymore
Kirby64|3 months ago
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.
ricardobeat|3 months ago
arresin|3 months ago
NoSalt|3 months ago
Joshua-Peter|3 months ago
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