Help - completely overwhelmed by electronics but will do my best - Page 1
Forum section: electronics / beginners

author: John_
author_rank: Contributor
timestamp: December 23, 2021, 10:42:39 pm
content: Hi,after watching a video on youtube of "eevblog" and tutorials for a few hours, i finally decided to ask for help.Now years ago an engineer/electronician (in medical field?) made me a box to help me with chronic pain (i'm a painter)Since then i've used this device whenever i had to do intensive works, it helped after applying creams.I've misplaced the box and i do not know the person who made it (almost 30 years ago)I have no knowledge of electronics.This is what i remember and wrote about the device, from what was told to me.There's a 9v battery (common type), a dial on the front where this gentleman wrote0.5v - 0.9vand there was two plugs (?) to place cables (like electrodes cables on ebay).He had wrote that the current was4.0ua(constant) on the box.When we were talking i had wrote these, if they can be of help:"potential 0.7" "electrodes up to 200na"I just placed the electrodes after the cream when i needed on the skin (and turned the dial on 0.5v or 0.9v depending on the pain)I searched on medical websites and electronic forums and it seems it is called "electrotherapy/galvanic current".but none of the devices are similar, i asked at the electronic shop about this and they explained that i maybe should make a "voltage divider circuit" (but even after reading about this i didn't understand)The device REALLY helped after applying cream on the skin.I tried EMS/TENS device but the relief was not the same.Nowadays it might be even simpler to build a circuit like this (or to anyone on this forum)Providing informations I will build this and will acquire the tools necessary for the job, if it is not overly complicated.With all the things that is happening right now, i would really appreciate any help.Thank you for reading,Enjoy the holidays!John C. Terbe

author: bob91343
author_rank: Super Contributor
timestamp: December 23, 2021, 11:23:02 pm
content: John, it appears that it's a device for passing a small current through your body. But the characteristics of that current are unknown. Is it direct current? Or alternating, of what frequency? A 9V battery cannot pass much energy through your body, which is good to know.But without more information, I don't know how to help. Perhaps you can locate the one who built it, or perhaps you can find the unit. Your description isn't complete enough to know what this unit does.

author: xrunner
author_rank: Super Contributor
timestamp: December 23, 2021, 11:32:59 pm
content: QuoteWell ... I have no idea what was inside the box, and I do not want to provide any medical advice because I am not a doctor.The 4.0 ua may mean 4 micro amps (4 x 10 -6 amps). Potential may mean 0.7 volts which would be (could be) provided by the 9 V battery. 200 nA is 200 nano amps (200 x 10 -9 amps). That being said, I cannot know how these values were being provided by the box. Need a schematic diagram of the electronics. Something inside would need to control a current from the battery and since it's a medical device I cannot speculate on how that was done. It could be done via a variable resistor (potentiometer) but I do not have the medical training to advise further.

author: John_
author_rank: Contributor
timestamp: December 23, 2021, 11:46:47 pm
content: Hi bob91343 and xrunner!from what i read it is direct current, as the device seems to be referred as a "iontophoresis circuit".This is what i have found:Galvanic Current – Based on the concept of galvanism is a direct, constant, unvarying current. Current is delivered with electrodes reacting as a positive and negative force to create chemical or physiological effects. Galvanic current reacts on sensory nerves and motor nerves, instigating a prickly or stinging sensation and is generally used to introduce solutions into the tissue (iontophoresis) or for disencrustation.This is exactly the effect i have from this device.Except that there are no sensation (only the cream when it is applied), other devices are very different.Based on notes about the device it is powered by a 9v battery but the "output" is 0.5 to 0.9v and the current is 4ua (as you correctly explained it is µa, as i just learned).Does this help?There are constant voltage and current modules (on ebay), but the output is very different (the person insisted on constant "µa")Thank you for your help!

author: Kim Christensen
author_rank: Super Contributor
timestamp: December 23, 2021, 11:58:51 pm
content: QuoteTake a AA or AAA battery (1.5V) and hold it in your hand or touch both ends at the same time... Do you feel anything?I doubt you can feel these voltages, let alone voltages between 0.5V and 0.9V, unless you've got a cut or something.

author: jpanhalt
author_rank: Super Contributor
timestamp: December 24, 2021, 12:16:08 am
content: Use of low (or fake) currents to cure or remedy many disorders has been claimed for decades. Andy Flind had a DIY project that claimed to cure almost anything, including infectious diseases. He achieved some acclaim, but died June 5th, 2004 from a rapidly fatal disease.* Never could get a copy of his death certificate despite trying. I wondered whether his battery died just before he succumbed. In other words, I consider his device and many of the others from early to late 20th century to be scams, snake oil.On the other hand, legitimate research has found some benefits ranging from relief of chronic pain, expedited healing (particularly bones), and specific nerve stimulation (e.g., vagal nerve stimulation). Search on TENS (transcutaneous electrical nerve stimulation). Legitimate medical institutions, such as the Mayo Clinic, have published on it.The literature is too extensive to review here. If you have a local university-affiliated hospital talk to a physician there or one you trust about it. Departments of neurology or pain management would be the places to go for your question. There may be help, but it is not a cure all as Find claimed. Nor is it for a DIY'er.NB: The US FDA has some regulation on use of electrical stimulation.*From his obituary: Andrew James C. Flind was born in 1944 and died in Devon, Somerset, England at age 60.EDIT: Added links and corrected spelling of "Find" to "Flind."Here's a link to some of his zappers:https://moam.info/virus-zapper-everyday-practical-electronics_5a1c122e1723ddfe383526e3.htmlhttps://www.epemag.com/vault/0302.htm(March,2002)Apparently for sale (Original, March, 2002)http://zappers.narod.ru/Another homeopathic/naturalist "curer" Hulda Clark attained notoriety in the US. Her products are still sold in ebay, Amazon, and a site in her name. She died of cancer in Chula Vista,CA. One of her business locations was Tijuana, Mexico (just across the border). She also was subject to several enforcement action and lawsuits.

author: John_
author_rank: Contributor
timestamp: December 24, 2021, 12:32:59 am
content: Hi Kim Christensen and jpanhalt!After years of various paints and resins i am well versed in allergic contact and chronic effects and the various dermabrasion treatment (at least once a month).I can compare the other device i tried (EMS/TENS) the "box" clearly made a difference (even years ago)I hope i'm not being taken the wrong way here but i just want to "replicate" this device (similar output), i understand what the litterature may say but i'm result oriented and i stand by the results of what i can still do in my work to this day.When you paint for hours everyday since the 70s, you can tell when something helps you! (and wishful thinking "treatment" does not help a steady hand and mind nor keeping contracts!)

author: jpanhalt
author_rank: Super Contributor
timestamp: December 24, 2021, 12:50:32 am
content: So, you had a mysterious box with some wires in it that made you feel better. The biggest problem is pain research is "placebo effect." In some studies it is as good as morphine.Sorry, I hoped to help you. But it seems that will be impossible. Good luck.

author: xrunner
author_rank: Super Contributor
timestamp: December 24, 2021, 12:56:23 am
content: Even allowing for the most rudimentary circuit of a battery and a potentiometer, with the resistance of your skin as the "resistor" completing the circuit, you would have to calibrate the output current. If you wanted to allow the same current you would need an instrument that would be able to accurately display these small currents.I don't think, with a cream on your skin, it's going to give a very repeatable "circuit" each time, so in my mind you'd need a micro ammeter as part of the instrument. I do not see how the original box would have been able to provide a very accurate current without a meter. I have no idea at all what these small currents mean to any medical healing - that is above my pay grade.

author: John_
author_rank: Contributor
timestamp: December 24, 2021, 01:53:27 am
content: Glad to see many replies!my apologies if i wasn't clear jpanhalt so let me elaborate (feels like sunday at the family reunion!)I've had 3 knee "surgery" (in the mid 60s not a fun ride), worked in central africa for more than 10 years (not sure even placebo might help with bilharzia and consort! which i can tell you never really leaves it's the kind of gift that keeps on giving) and kept painting be it commercial (boats) and private (antiques) till today.Didn't expect to be put on the spot in what i took for a "gentler" part of the forum or as my french comrades used to say "une mise en bouche or entrée en matière".i hope at least your comment have proved useful to confirm your view, that is if you ever had to experience similar health issues (to test if placebo is of any comfort)if not my sympathies you'll get a chuckle.xrunner,I was at the workplace of the gentleman, so i know that he calibrated the circuit and tested it (as he offered me the device and explained the use of the circuit at the time)I usually do not question the eastern european craftmanship nor the kindness (in this case a schematic would've been of help!).Would a calibration have been sufficient (with the ammeter all those years ago?) i never opened the device (but have seen each steps).Is there any way i can replicate such a configuration (with the ammeter of course)The "cream" bioavailability is far from being excellent (as mentioned allergic reaction and "trade" tough skin) which from the litterature indicate that "iontophoresis device" might help with increase availability (surprising isn't it? seems like the litterature might agree with the MD's observations who follow me since the 2000s)Thank you for commenting on the question.If this post lacks proper etiquette let me know! (i am not used to forums).

author: bob91343
author_rank: Super Contributor
timestamp: December 24, 2021, 02:59:23 am
content: I found this:https://www.healthline.com/health/sweat-electrolytes-testBut so far have not been able to find specific parameters or even a DIY project.Well I found this:

author: bob91343
author_rank: Super Contributor
timestamp: December 24, 2021, 03:08:52 am
content: I just watched that video and it looks like the pans are touching each other, which should not be.

author: Kim Christensen
author_rank: Super Contributor
timestamp: December 24, 2021, 03:10:09 am
content: Quote from: John_ on December 24, 2021, 01:53:27 amThe problem with your post isn't about etiquette at all. It is more of a technical issue about something called "ohms law".Ohms law is a simple mathematical formula. If I explain it to you, it may help you understand why we can't really answer your question properly with the informative you've given us. Ohms law states that if you put a voltage across a resistance then a set current will flow. The formula is thus:Current = Voltage / ResistanceThis formula can be rearranged if we don't know the Resistance but do know the Voltage and Current:Resistance = Voltage / CurrentYour skin has resistance. This resistance will change with moisture, how far apart the electrodes are placed, how much cream you smeared on, etc...So the problem comes when you say "theoutputis 0.5 to 0.9v and thecurrentis 4ua". If we put these numbers into the Ohms Law formula we know that your skin resistance MUST between 125Kohms (0.5V / 4uA) and 225Kohms (0.9V / 4uA)...But if your skin resistance is not between 125Kohms and 225Kohms no device can satisfy BOTH the voltage (0.5V to 0.9V) AND the current (4uA) at the same time.ie: If the skin resistance between the two electrodes was 50Kohms and we put 0.5V across them, then 10uA will flow (0.5V /50K)... But if we change our minds and decide to set the current to 4uA then only 0.2V (4uA * 50K) would appear across the two electrodes.

author: John_
author_rank: Contributor
timestamp: December 24, 2021, 11:50:06 am
content: Hi bob91343 and Kim Christensen!thank you for explaining the Ohms law formula in such details, i understand better now what the issue is.based on available data 225kohm is in the range of dry skin (and callous tissues), 125kohm for hydrated (stratum intact).50kohm with dermabrasion treatment and cream and/or gel.I found this:"The removal of the stratum corneum is commonly used in esthetic applications for skin remodeling, and in methods of preparing the skin for drug conveyance, such as iontophoresis. They interest us only for the electrical measurements taken to correlate quantity and thickness of removed material and skin resistance.""Tape stripping seems to increase ion mobility by two orders of magnitude (that is a hundredfold increase).12 This correlates very well with the findings on microdermabrasion, which decreases resistance from thousands of kΩ to tens of kΩ.15 Gill and colleagues15 give a value of about 20–80 kΩ for skin resistance after complete stratum removal.""To give an order of magnitude for skin resistance, in an earlier work Inada et al16 had given 12–120 kΩ/cm2, while Kalia and Guy11 found a value of 187 kΩ for the real part of the complex skin impedance in hydrated skin with intact stratum corneum"Then i could do three circuits 0.2v, 0.5v and 0.9v (could the person have placed two circuits and toggle with the dial?) in three boxes.I also found a thread about a circuit with similar values (this seems to be about "tissues samples") but the battery is a 3v button cell. here is the answer to constant of 1µa and 0.9v with a 3v battery:"After doing a bit of googling I now think you could use a 3V lithium cell to power a constant-current source. There are micropower 1.25V voltage references available (e.g. LTC6656-1.25) and micropower op-amps (e.g. MAX40006). Something based on the attached circuit might meet your requirements, so far as I understand them.""The Sample current here is 2μA, set by resistor R1 (increase R1 to reduce the current, reduce R1 to increase the current). The LT6656 draws <1μA and the MAX40006 draws <5μA, so the lithium cell should run for a long time.""Simulation suggests that if R1 is increased to 1.5 Megohms, the constant current becomes 1μA and the voltage across the sample remains below 1V for all sample resistances up to 1 Megohm. [Note: I don't have a Spice model of the MAX4006. My simulation used the LTspice Universal op-amp2 model, so isn't precise]."bob91343,This might be of help?http://www.nlvocables.com/blog/?p=609Thank you for the time you take to explain it in details.

author: Simon
author_rank: Unknown
timestamp: December 24, 2021, 12:13:49 pm
content: I would suggest you look into a new one. These devices are now readily available rom simple and hopefully cheap pain relief to more advanced adaptive devices such as the Skenar I use. Depending on your budget a home use skenar is a few hundred pounds.

author: wizard69
author_rank: Super Contributor
timestamp: December 25, 2021, 12:36:55 am
content: This is one of those things where i really believe you need to seek a medical professional. Even if such a box works you will want it to be safe to use and in a case like this it really needs to be an FDA approved unit.Honestly there are so many issues with pain that it is extremely difficult to find the right treatment these days. It may be that more modern solutions exist. By the way that cream you are putting on could be the solution with the electronics just giving you time for the cream to work.

author: John_
author_rank: Contributor
timestamp: December 25, 2021, 05:12:20 pm
content: Hi Simon and wizard69!i have looked at the Skenar description, and the research the device is based on (very interesting, there is a lot to read!)Thank you for the suggestion.I have also found the SIS Electro based on ultra low intensity direct current (LIDC), this might also be of interest to you.From the litterature i have found iontophoresis is a "transdermal delivery system as charged molecules of medication penetrate through the skin to underlying tissues via wired or wireless skin patches."This would be interesting to see if a simple project like this one (and the measurement of skin resistance parameters) can influence transdermal delivery (and to test both electrodes placements, voltage, and µa)As a project i want to try a LIDC circuit (from what i read a voltage divider with potentiometer, and calibration with a multimeter of the load should suffice as a test project) but as the skin resistance varies greatly a potentiometer would be more suitable.A simple LIDC is a battery, linear potentiometer and analog µammeter, is that correct?The issue i see is that fine adjustement is needed as Kim Christensen noted (as 4µa is the reference)Let's say 9v with the linear multi turn potentiometer as voltage divider up to 0.9v, max reference for skin resistance 250k , 0.9v (3.6µa * 250k)I don't know if the tolerance is similar in voltage divider as it is as variable resistor.But if the tolerance is 20%, it's 1.2 (4µa * 300k) but in range with 0.8 (4µa * 200k)These are three option for a "simple "LIDC":Battery, Potentiometer, µammeter.Battery, resistors.Constant current circuit (LTC6656 and MAX40006 as example like the thread mentioned)in application:test various skin resistance placements and condition (dry, hydrated, stratum treatment) with a multimeter (i've looked at data with baseline and distance), place resistor with similar value as load to test the circuit, adjust µammeter with the potentiometer to match values before placing electrodes on skin (measure changes in skin resistance)What i do not understand is the mention of Vout upper and lower (R1 - R2), is there a different potential at the output of a voltage divider circuit and the "loading" effect (possible need to buffer the output first?)I thought that with a potentiometer as voltage divider, it's the value of R1+R2?see:https://electronics.stackexchange.com/questions/328212/voltage-divider-equation-with-load-on-outputHave a great day!

author: CaptDon
author_rank: Super Contributor
timestamp: December 25, 2021, 09:25:27 pm
content: I bet that box was nothing more than a 9vdc battery which had a power switch (possibly located on the rotary potentiometer) feeding a 100k series resistor to a 10k pot with the low side of the pot back to battery negative. That would give you the voltage and current limits mentioned but not well regulated. Apparently the (can we say electrolysis) helped whatever medicine was in the cream to better penetrate the skin and arrive at the locations of soreness. I still say 90% placebo effect. How did you know how high to turn it up?Was more ALWAYS better or was there some 'sweet spot' setting?Not to little, Not to much??? I seriously doubt the box had any 'active' circuitry??? As for placebo I saw a person get falling down drunk on non-alcoholic 'ginger beer' and I personally know a guy who wrecked his car thinking he was having an LSD trip when in fact the tiny little tablets were made from chalk!! 4ua of current, doubt it has any measurable effect in real double blind studies with one exception, among audiophools it probably increases the depth of the sound stage and adds certain clarity to the ultrasonic harmonics of audio signals above 18Khz but ONLY if the little box cost more than 2 kilobucks and only when you hold it near the center of your head with each of the two clip leads attached to an ear lobe.

author: John_
author_rank: Contributor
timestamp: December 25, 2021, 10:55:50 pm
content: Hi CaptDon!as i don't find believing nor betting in any matter a productive endeavor i abstain to comment on other personal belief system.The placement of electrodes at 0.5v was beneficial with the cables provided, when i changed the electrodes (and dermabrasion treatment) 0.9v improved tissues conditions following applications (mentioned in litterature with the principle of electrophoresis a transdermal method) of the dermatological preparation (more than ultrasound without dermabrasion)The cream is prepared for patient with acute contact allergy (paint and resin works) and monitored by the dermatology department.there are published peer reviewed and available studies, clinal trials, treatments in public and private institutions and patents on both iontophoresis (movement of ions) and LIDC.Effects in vivo and in vitro is researched and documented in µa in various pathologies and mechanism such as galvanotaxis being influenced (in vivo treatments of ulcers and dermatological conditions documented and details published)Anyone can access documents published on the subjects, as well as informations on researcher who worked on these studies and/or trials and if any personal expertise surmount the data published feel free to refute and/or propose a counter study by replicating both methodology and parameters.This should be beneficial to the advancement of the medical field if there is any validity to this kind of enterprise and amount to more than personal opinions.On the matter of electronics, does the informations provided in the previous message could be applied with relative tolerance to both voltage and current (µa)?Is there any similar available components than the one mentioned for the constant current circuit?Thank you!

author: Terry Bites
author_rank: Super Contributor
timestamp: December 26, 2021, 02:53:08 am
content: Iontophoresis is achieved with a constant current supply and usually with good skin prep. it really works. You can push active moleculeds down into skin and drive it latterally towards the second electrode.Polarity matters, the drug could be cationic or anionicIt looks as if the ccs has an ouput of 4uA and a complance range of 0.4 to 0.9V. That migh be a typo (0.4-9V) since the current is fixed increasing the complance range wont be a problem.IEC 60601 is only concerned about limiting current through applied parts. So heres a stable 2xAA current source. The bias LED Vf drifts in the oposite direction to the pnps Vbe.As shown its set close to 4uA for loads of zero ohms to megohms. Its stable to 5% over a 10-50'C range. And the red high eff LED shows you its on. Tweak the 270k if you need a different current.Note that the ground is the curcuit ground. Do not earth.....!Here's blast from the past: I was asked to help fix an iontophoresis ccs.The "constant currnet source" was made from an autotransformer, a wirewound pot, an 1N4007 a 100u caP, a Vu meter with paper tabs and some binding posts. Terrfying!I junked it and made a 60601 compliant unit. The surgeon who built in his shed said he was a keen ametuer engineer- so I said thats great, I'm a keen ametuer surgeon. Ooo,If looks could kill!Still severed limb reattachment progressed.

author: CaptDon
author_rank: Super Contributor
timestamp: December 26, 2021, 03:10:53 am
content: Just for giggles I tried an experiment. I connected a LION battery (low in charge) producing 3.0vdc with a microamp meter in series and when holding one lead in each hand I got about 10ua with damp fingers and about 6ua with dry fingers. I next placed the leads on my tongue and got about 70ua of current with only the tiniest of sensations of current flow. I suspect at .5 to .9vdc you would have to have very clean skin and cream to get 4ua of current flow. B.T.W., the microamp meter is a low series resistance lab unit so it was no a limiting factor in the current flow. Some very sensitive current meters have an internal resistance in the hundreds of ohms and their functional use can be very limited as they put a huge upset into the circuit under test. Cheers!!! The bit about the Audiophools was just a joke!!! Those folks are willing purchasers of the worst snake oil magic devices and their imagination is well documented.

author: John_
author_rank: Contributor
timestamp: December 26, 2021, 11:05:30 pm
content: Hi Terry Bites and CaptDon!Terry Bites,thanks for the provided schematic!In studies were electrolysis of the tissues were avoided the data indicate that it is detected at 1.1v (true current increase is noted at potential of 1.5v and higher)Exponential increase in current beginning at 0.8v to 1.0v (similar increase in electrolysis rate)Possible circuit configuration (a generator based on those informations for a study):Battery controlled by a field effect transistor Q1 and resistor R1, current flow through R1 establishes feedback voltage applied to the gate terminal of Q1. The signal cause Q1 to adjust it's resistance so that constant current is applied through patient resistance (from 0 to over 1 MOhm, and Changing R1 resistance changes magnitude of current)An alarm circuit (R2 and R3, comparator and buzzer) indicate when a voltage between patient leads exceed 1v.R2 and R3 form a voltage divider for voltage reference for the comparator.When patient circuit exceed reference voltage, comparator is switched on, sounding the buzzer (indicating electrodes placements and parameters to be adjusted)Thank you for any help on this!

author: John_
author_rank: Contributor
timestamp: December 29, 2021, 09:07:24 pm
content: Hi!I do not know if i can post link to the study as pdf in the thread.I don't understand comparators in circuit, in the examples i've seen sometimes V+ and V- are connected and sometimes they're not (in the study schematic only input and output).If i read correctly FET are JFET and MOSFET, is that correct? (FET (Q1) p-channel in the schematic)

author: gcewing
author_rank: Regular Contributor
timestamp: December 30, 2021, 04:42:49 am
content: Quote from: John_ on December 29, 2021, 09:07:24 pmSometimes power supply connections to op amps and comparators are not explicitly shown on schematics. If there are multiple devices in one package, the power supplies might be drawn on just one of the symbols, or there might be some indication elsewhere on the schematic, or they might just be omitted altogether. In any case, you should always assume they're there -- the circuit won't work without them!

author: strawberry
author_rank: Super Contributor
timestamp: December 30, 2021, 06:34:38 am
content: n JFET gate off ~-2Venchantment n MOSFET gate off ~+3Vcomparator is boolean logic device,if +input is more(1) than -input(0) then output is high(1)if +input is less(0) than -input(1) then output is low(0)

author: John_
author_rank: Contributor
timestamp: December 30, 2021, 11:10:51 pm
content: Hi gcewing and strawberry!so always implied but not always shown.As the reference is 1v max, is there differences with op amps as comparators? (i see LM358, LM393, LM741 as the most discussed and available)How to choose JFET? (apart from p-channel)

author: John_
author_rank: Contributor
timestamp: January 04, 2022, 08:22:09 pm
content: Hi,still on this project.Any recommendations for simulation circuits software? (who can also list alternative components or similar function with a database)Thanks!John.

author: Capernicus
author_rank: Frequent Contributor
timestamp: January 04, 2022, 09:30:47 pm
content: Whatever you do... when u finally start being to understand electronics DONT FORGET HOW YOU BEGAN!!!* a) YOU WILL BE HAPPIER PERSON. u wont take it all for granted.* b) you will be friendlier to other beginners.* c) youll be able to teach beginners better if u can remember being one!!!

author: John_
author_rank: Contributor
timestamp: January 11, 2022, 11:07:23 pm
content: Hi!I tried a few online circuits simulators and it's not intuitive (even for beginners) before trying LTSpice or other.About the circuit (already mentioned without values):As reference is 1v max for the comparator, taking into account skin resistance and electrodes placements, would it be better to have Vout at 1v or 0.9v for the voltage divider part of the circuit? (even if buzzer indicate skin resistance to be verifed and/or electrodes placement, the voltage would already be over reference and depend on reactivity to readjust)How to calculate the response of the comparator reference voltage switch on/off to the buzzer?Low power or precision type for comparators?Resistors (R1, R2 and R3) 1% tolerance.Q1 as JFET i found J174 TO-92.Thank you for any help!

author: John_
author_rank: Contributor
timestamp: February 26, 2022, 10:00:27 pm
content: Hi,What is the formula to know the current output of a voltage divider and how to calculate the drop response of voltage dividers with a load? (in this case skin resistance)circuit (No load)Vin - 1.5v (AA alkaline)Vout -0.9v (4µA)The values of the voltage divider cannot be accurately measured by the multimeter in the µV and µA, nA range, but checking the skin resistance (rest, dry and hydrated) with the multimeter as references for the tolerance related to time (ambient parameters, perspiration, etc...) the margin values could be maintained long enough to test the iontophoresis.I've seen probes "galvanic" devices, who use the anode (+) as contact on the skin and cathode (-) as smart sensors holding the device.I don't know if there are available (cheaper) alternatives for LT6656ACS6-1.25 and MAX40006, any suggestion?John.

author: Kim Christensen
author_rank: Super Contributor
timestamp: February 27, 2022, 05:15:06 am
content: Quote from: John_ on February 26, 2022, 10:00:27 pmWhat you want to figure out is the Thevenin equivalent of the voltage divider circuit. Once you do that, it's simple to see how it would behave under various loads. See attached.

author: John_
author_rank: Contributor
timestamp: March 01, 2022, 11:54:38 pm
content: Hi,thank you Kim Christensen for the information on the Thevenin equivalent (the Thevenin Theorem and the notion of Vth and Rth) much appreciated.The voltage divider seems like a suitable configuration for in vitro (without electrodes displacement and varying resistances) but a constant current circuit (in vivo) would help to avoid electrolysis (and electrodes adjustements)Here is a circuit i found with different values and requirement (for in vitro studies) but the current is constant (see attachment)I've looked at the precision voltage references series data and i don't know if there are alternatives to the LT6656ACS6-1.25 and MAX40006 (if a 3v or a 9v battery is used)John.

author: Kim Christensen
author_rank: Super Contributor
timestamp: March 03, 2022, 03:24:58 am
content: Quote from: John_ on March 01, 2022, 11:54:38 pmI can't see the JPG (schematic) without signing up. Could you download it and attach it here instead? Then everyone here can see it easily...QuoteWhile not as fancy, a TL431 (2.5V ref) could be used with a few circuit modifications. It'll be precise enough I would think.

author: John_
author_rank: Contributor
timestamp: July 07, 2022, 10:04:35 pm
content: Hi,i found the original schematic but without any components values.There is no info on Q1 and the comparator.if any one can help (or try to simulate this circuit) i would really appreciate it.Thank you.John.

author: Kim Christensen
author_rank: Super Contributor
timestamp: July 10, 2022, 05:46:38 pm
content: Q1 is a P-channel J-FET setup as a current source (with R1) providing a constant current (within limits) to the two output terminals ( downward pointing arrows with + & - )R2 & R3 set the trip point for the buzzer which sounds when the voltage on the two output terminals goes out of bounds.Note: Circuit could also be built with a more common N-channel J-FET, reversing the battery polarity, and swapping the output wires.

author: John_
author_rank: Contributor
timestamp: July 11, 2022, 02:41:31 pm
content: Hi Kim Christensen,i have simulated voltage dividers in software but not this schematic.The description of this circuit has this mention:"This signal cause Q1 to adjust it's resistance so that constant current is applied through patient resistances from zero ohms to over one megaohm"So R1 provide current reference and the voltage divider the voltage reference (the buzzer could also be a led if this is an indicator to adjust the placement)I don't understand what is the comparator component in this schematic and why the values are not included in the schematic notes (clearly would make things easier as references)I have looked at the TL431 and it's very interesting but would it be similar as the MAX40006 (the TL431 description is 2.5v reference and comparator), as you mentioned a few circuit modification.It may interest others who are also learning about electronic components:https://www.righto.com/2014/05/reverse-engineering-tl431-most-common.htmlIs there any way with "easy to find" components to design a precise constant µ current circuit? the only ones i found are very specific like the MAX40006 mentioned and this:https://www.eeweb.com/10-100-micro-amp-constant-current-source/Thanks again.John.