Hacker News Board Hacker News, browsed like a classic message board
Live data from Hacker News

Show HN: 32V TENS device from built from scratch under $100

littlemountainman.github.io

Post reply on HN
Print view View original

21–27 of 27 posts

Re: Show HN: 32V TENS device from built from scratch under $100

#21

Post by dmitrygr »

shadowpho wrote: post #20
Kirby64 wrote: post #16

Earlier quoted context omitted.

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…

^^ this

Re: Show HN: 32V TENS device from built from scratch under $100

#22

Post by autonomydriver »

zhouyisu wrote: post #13

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.

Re: Show HN: 32V TENS device from built from scratch under $100

#23

Post by autonomydriver »

lambdaone wrote: post #8

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 :)

Re: Show HN: 32V TENS device from built from scratch under $100

#24

Post by autonomydriver »

sowbug wrote: post #11

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.

Re: Show HN: 32V TENS device from built from scratch under $100

#25

Post by autonomydriver »

clnhlzmn wrote: post #9

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

Re: Show HN: 32V TENS device from built from scratch under $100

#26

Post by mrcartmeneses »

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

Re: Show HN: 32V TENS device from built from scratch under $100

#27

Post by atombender »

mrcartmeneses wrote: post #26

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?
Post reply on HN