nerve stimulator - Page 1
Forum section: electronics / projects

author: biomedical man
author_rank: Newbie
timestamp: June 15, 2022, 05:41:13 pm
content: hello there iam a biomedical engineer at my last yeari am working on nerve stimulation deviceand i need help to find the best circuitry for that .we know that nerve is stimulated with milly ampere like 50 mA maximum and the skin resistance is between 1 and 3 kiloso i used a transformer to Magnifeye the output volt from 5 to like 180 v {note the pulse width around 50 us}buti need help withamplification circuitwithfetandop ampto feed the transformer with fixed current to beindependent of the {load} skin resistancei prefer to use closed loop with current feedback to make the system more stable and to get wilder range

author: Gyro
author_rank: Super Contributor
timestamp: June 15, 2022, 05:58:00 pm
content: It really wouldn't be safe for members to give you circuit advice while you think that 50mA and 180V are acceptable values for nerve stimulation.

author: CJay
author_rank: Super Contributor
timestamp: June 15, 2022, 06:17:19 pm
content: Quote from: Gyro on June 15, 2022, 05:58:00 pmSounds rather more like a torture device at 180V 50mA

author: biomedical man
author_rank: Newbie
timestamp: June 15, 2022, 06:26:39 pm
content: rightbut that is the limitation of the volt and amp i want to usei am using a micro seconds puls width here

author: SiliconWizard
author_rank: Super Contributor
timestamp: June 15, 2022, 06:27:28 pm
content: Uh yeah. Ditto.Just an additional point: if you think of stimulating "nerves" through the skin, then you're looking at doing TENS. At this point, although I've seen some other potential uses of TENS, it's mainly used for pain control and the well known muscle stimulation devices. What exactly do you want to achieve with TENS?With the max values you talked about, such a device could lead to anywhere from very uncomfortable sensations to a lethal result.In particular if it's not properly isolated, or if you put the electrodes too close to the heart region, or simply too far apart from one another on the body. If the person has metallic implants of any kind, things could go sour also real quick.The usual approach for the front-end of such stimulators is to implement controlled current sources, for instance voltage-controlled. Such current sources (for general purpose) are actually a rather FAQ on this forum, so you'll find tens of suggestions.But again I would advise against doing that unless you really know what you are doing, or at least unless you intend never to use it on anyone and just keep it as a lab project for the sake of it. It could again be lethal. In any case, using it on anyone else but yourself, unless you managed to have it certified, would also be illegal.

author: Gyro
author_rank: Super Contributor
timestamp: June 15, 2022, 06:45:33 pm
content: Quote from: biomedical man on June 15, 2022, 06:26:39 pmAs SiliconWizard mentioned, there are legal and safety implications of such devices. Such things as galvanic isolation from mains power sources are critical to safety. You would need to providemuchmore information about things like pulse waveforms to convince people that you know what you are doing. For instance, driving the transformer with a fet would lead to a flyback type situation with poor control of waveform. Driving it with a push-pull amplifier would be much more appropriate to providing controlled waveforms, I would hope that your course had covered such things by now.I am by no means an expert (I did study some bioscience at Uni before changing courses) but I think pulses in the microsecond range would be far too short to provide effective stimulation of nerve cells - being way outside their operating bandwidth. I would have though that cell damage would be a more likely result.

author: biomedical man
author_rank: Newbie
timestamp: June 15, 2022, 06:47:23 pm
content: first yes its tens devicesecond yes i know its risks and hazards :dont use it with pregnant woman or with defibrillator or any patient use metals in there body and more ...and last yes is i need an current control from voltage control with op amp and current feedback control like this oneit is pain to simulate it on proteus and i need a way to calculate the suitable amplifier and resistors all again

author: Haenk
author_rank: Super Contributor
timestamp: June 15, 2022, 09:39:14 pm
content: I'd say "buy a cheap TENS device (a real certification, like CE, is a must), take it apart and reverse engineer it". Then you have a device that works and does not kill you - and you could refine from there on.

author: rfclown
author_rank: Frequent Contributor
timestamp: June 16, 2022, 01:13:43 am
content: Quote from: Haenk on June 15, 2022, 09:39:14 pmThis suggestion is good for a starting point into educating yourself on TENS devices. Your questions demonstrate that you need to do more self education before asking questions. Read technical articles on TENS devices and therapies. Read patents on devices. I've worked professionally with implanted neurostimulators, and I can say that you need to educate yourself, and this forum is not the place to start. Start with reading. Google is your friend. When I was interested in EEG years ago, I found a forum dedicated to building a home device (http://openeeg.sourceforge.net/doc/) and asked questions there. Find a forum dedicated to TENS, and read everything before asking questions.

author: biomedical man
author_rank: Newbie
timestamp: June 16, 2022, 06:13:08 am
content: thanks but i dont want to amplifie the nerve signal i want to amplifie signal to stimulate the nerve

author: jonpaul
author_rank: Super Contributor
timestamp: June 16, 2022, 08:16:25 am
content: Bonjour cher Monsieur1. Bioelectricity and électrique nerve stimulation was discovered by Galvanni 1771 and Volta 1791, in Italy, using a battery ( Volta Pile) to make a frog's leg jump.https://datatorch.com/data/Electricity_and_life_Galvani_experiment_with_frog_legs2. Biomédical R&D and education projects normally use small animals or cadaver muscles and nerves for experiments, not live human subjects. At CAL TECH in 1960s..1970s, toad bladders were used in nerve stimulation work.3. Driving a transformer with an opamp is not trivial.4. skin resistance is only 100s ohms to megohms, depending upon the dry, wet, skin type, depth of electrode insertion, etc. Suggest that you should check electrodes, the skin resistance definition and research more deeply.5. nerve transmission speed is an indication of nerve functions and health. Professionals have instruments to measure the nerve transmission speed, usually 100s uS...mS.Bon courageJonjust the ramblings of an old retired EE

author: Terry Bites
author_rank: Super Contributor
timestamp: June 16, 2022, 02:55:09 pm
content: You're right, we shouldnt promote the constuction of medical devices outside of a professional setting.

author: poorchava
author_rank: Super Contributor
timestamp: June 16, 2022, 06:14:34 pm
content: I have built something like that. It was a power stage for a device that was supposed to work around neurological deficits after accidents (damaged nerves in limbs). The idea was that the neural net would figure out what the user wants to do, and then generate pulses to make muscles move in appropriate way. The current source was controlled by a DAC from an STM32F205 uC.In our case the hardware had to be very small. It ended up being a boost converter generating 110V at about 100mA, followed by a FET bridge that had a linear current source at the low common point. I have taken apart TENS device or two before and one of them used a similar approach to mine, the other used some arrangement with 2 flyback fransformers. Not sure how exactly that one worked though.People who are scared about 180V and 50mA: if you shape the pulses correctly it's totally safe I can't disclose that part in detail, I'm only gonna tell you that pulses need to be symmetrical to keep DC component at 0, so as to not cause electrochemical reactions in the body. Also, 110V at 100mA is not immediately lethal. If this is gonna fail, you're gonna get DC electrocuted which doesn't cause ventricular fibrillation. It will cause a tiny burn at the contact points after some time and is quite unpleasant, but that's all. If you ran this for a few hours you could maybe risk hemolysis of blood, but that's a really remote possibility.Burns and/or irritation from badly attached electrodes are common. Patch electrodes need the outer layer of skin to be peeled which is quite painful. An alternative to this are needles that you have to push into the outer muscle tissue layer. Much better performance, actually less painful than peeling for patch electrodes. The only problem is that they can cause inflammation after some time.Yes, I have been experimenting on myself when building that. And yes, the client paid enough))

author: CJay
author_rank: Super Contributor
timestamp: June 16, 2022, 06:35:28 pm
content: Yeah, I've played with biphasic nerve stimulation before.There's no way I'm giving advice to a random on a forum

author: coppercone2
author_rank: Super Contributor
timestamp: June 17, 2022, 04:52:08 am
content: you should get help from a professor, this is too serious for the forum