What value of resistors do I need and a sanity check

[davenn]

The right side of the potentiometer needs to be connected to the same place as the other four resistors, i.e. to the left side of the fuse, and you also need a resistor in series with the potentiometer.

Thanks Dave.

yeah ok it is but he, for what ever reason, wanted that isolated from the other 4 outputs .... hence the diode

personally I would do as you said and put the ammeter in the final output right before the fuse

just get a final comment before I post the revised diag


D

 

[KrisBlueNZ]

yeah ok it is but he, for what ever reason, wanted that isolated from the other 4 outputs .... hence the diode

I think his reason was that he thought you could indicate the setting of the potentiometer with the meter. But that's not possible. And the diode won't work, because the LM334's current is set by the resistance between -V and Rset and you can't have a series diode in that path.

 

[davenn]

I think his reason was that he thought you could indicate the setting of the potentiometer with the meter. But that's not possible. And the diode won't work, because the LM334's current is set by the resistance between -V and Rset and you can't have a series diode in that path.

ok will remove it

D

 

[davenn]

OK revised version

Thanks Kris for the input

cheers
Dave

 

[jjanes]

Dave, I do thank you for your help your diagram is very good. I guess because I also put time in mine to get those types of responses to my very first post just put me a bit off.
As far as your diagram it is very easily read and I understand what is being done. In KrisBlueNZ post he mentioned using the 5 pole switch for the pot on 5 and with the dual throw it isolates the circuitry yet keeps them connected visually with the LEDS. With some experience I will also be able to come up with diagrams like that I just need some experience thinking like that and also knowing that I need to do something like that in the first place it will come with experience which you definitely have.

Kris I do understand and I do hold all your data as informational and will if I can use at my own risk but thanks for reminding me.

A question regarding LM334Z and the 470uf cap, How do you find out about things like the fact it is not only a current regulator but is also a temperature sensors as well
and that the unit needs to be fully connected or else it act in the opposite manner and not give a soft start and finish.

I do thank everyone for their help

 

[KrisBlueNZ]

Nice one Dave, that looks just right.

In KrisBlueNZ post he mentioned using the 5 pole switch for the pot on 5 and with the dual throw it isolates the circuitry yet keeps them connected visually with the LEDS. With some experience I will also be able to come up with diagrams like that I just need some experience thinking like that and also knowing that I need to do something like that in the first place it will come with experience which you definitely have.

That's right, it's just a matter of experience and knowing what's available and how things are done. You can learn a lot from taking things apart. You're supposed to wait until the thing is broken, but when I was young I discovered a shortcut - break it in the process of taking it apart. Then you don't have to try to put it back together.

Kris I do understand and I do hold all your data as informational and will if I can use at my own risk but thanks for reminding me.

It's as much for my own peace of mind really. Equipment that is intended for direct connection to the human body has to be very carefully designed and put through strict tests before it can be approved. I can't even tell you that it's safe to feed current through your head. I do think that that circuit will do what you want, but that's all I'm prepared to say!

A question regarding LM334Z and the 470uf cap, How do you find out about things like the fact it is not only a current regulator but is also a temperature sensors as well

Read the data sheet! http://www.ti.com/lit/ds/symlink/lm134.pdf

... and that the unit needs to be fully connected or else it act in the opposite manner and not give a soft start and finish.

That comes from understanding how that circuit will behave when there is no load, and knowing what capacitors do. A capacitor stores energy. It's a lot like a rechargeable battery, but batteries store much more energy for the same size. When there's no load on the circuit, the current from the LM334 will charge the capacitor, and the output voltage will increase until it's near the battery voltage - say 10 volts. At this point, the capacitor contains energy stored as charge. Since the capacitor was connected to the electrodes, the current regulator circuit will not limit the current that the capacitor can supply to the electrodes. When the electrodes are connected, the current flow will only be limited by the resistance between the electrodes, and will be typically a lot higher than the wanted current, until the capacitor discharges. A 470 uF capacitor can store enough energy that this might be a problem in this case.

 

[KJ6EAD]

Nice schematic Dave. It's so much easier to look at.

Skin resistance being what it is, I expect the regulator will always output it's maximum available voltage and still not achieve even the 0.5mA of the lowest setting unless the skin is wet.

 

[KrisBlueNZ]

Skin resistance being what it is, I expect the regulator will always output it's maximum available voltage and still not achieve even the 0.5mA of the lowest setting unless the skin is wet.

See http://en.wikipedia.org/wiki/Transcranial_direct-current_stimulation
The electrodes are prepared with saline solution and the skin at the contact area is prepared with "electrode cream".

 

[CDRIVE]

Dave, you did a great job inverting, transposing and in general, making the the schematic easy to follow and understand.

Kris, you never cease to impress me with your lengthy attention to detail. Few of us have the motivation to type that much. You never leave the OP lacking pertinent and concise information.

jjanes, this forum is comprised of humans. Humans have personalities, though I sometimes wonder if Kris is actually a Vulcan. Anyway, there are thousands of chips out there and it's doubtful that all of us are familiar with all of them... Vulcan's excluded. So, when an unorthodoxly constructed schematic is posted it makes it that much harder to follow. Hey, we know that you just built upon the existing schematic but that's what scares me the most. It's obvious that the original schematic was not drawn by an experienced Electron Head. Even the symbol he used for the LM334Z resembles a logic block more than an analog device. When you compile these facts it really begs the question; Does this guy have the knowledge to be passing electron current through anyone's head?

Nice schematic Dave. It's so much easier to look at.

Skin resistance being what it is, I expect the regulator will always output it's maximum available voltage and still not achieve even the 0.5mA of the lowest setting unless the skin is wet.

I did a very uncontrolled unscientific test. I dampened my temples with nice salty saliva and measured the resistance with meter probes. I actually applied pressure where the points were starting to penetrate the skin. The average reading was 120K. Giving the benefit of the doubt I rounded that all the way down to 100K. At 12V I = 120uA. Since those results didn't convince me, so I did the classic tongue test. Can't beat it for human conductivity. The results were still high with quite a bit of bobble. Hard to say, with all the bobble, but 28K was the lowest I attained. That puts I = 428uA @ 12V. Electrode pads would be nice to have as I'm still not convinced of the actual resistance.

By the way, I did a short search for a 5mA pico fuse. Sadly, I've never mastered the Digikey search engine but I suspect finding a 5mA fuse might be analogous to searching for Hens Teeth. I'm not saying they don't exist. I'm skeptical but technology is changing all the time.

Just in: Scientists believe they have discovered the first documented remains of Hens Teeth in Australia! New Zealand is disputing the find, claiming their Hens have always had teeth.


Chris

 

[KrisBlueNZ]

Kris, you never cease to impress me with your lengthy attention to detail. Few of us have the motivation to type that much. You never leave the OP lacking pertinent and concise information.

Thanks Chris I obviously have much too much time on my hands. I need a job :-/

It's obvious that the original schematic was not drawn by an experienced Electron Head. [...] Does this guy have the knowledge to be passing electron current through anyone's head?

Agreed. After reading the relevant Wikipedia page I can see a few things I would do differently if I was designing the current generator, but I'm cautious about suggesting anything because of the application. If it was an LED tester, no problem, but when you're connecting electrodes to people's heads, it's a different story!

I did a very uncontrolled unscientific test. I dampened my temples with nice salty saliva and measured the resistance with meter probes.

I think electrodes will have a larger contact area than meter probes.

By the way, I did a short search for a 5mA pico fuse. Sadly, I've never mastered the Digikey search engine but I suspect finding a 5mA fuse might be analogous to searching for Hens Teeth.

I'm not surprised. Perhaps the original designer put it in his schematic as an ass-covering measure.

Just in: Scientists believe they have discovered the first documented remains of Hens Teeth in Australia! New Zealand is disputing the find, claiming their Hens have always had teeth.

LOL Did you know that chickens, being descended from dinosaurs, actually have the genes to make teeth? I'm not making this up.
http://indianapublicmedia.org/amomentofscience/as-scarce-as-hens-teeth/
http://www.npr.org/templates/story/story.php?storyId=5230538

 

[CDRIVE]

I think electrodes will have a larger contact area than meter probes.

Agreed and I think I should have my head examined. The DMM that I used for my measurements is the same DMM that I carried with me for over a decade. It and its probes have been in and out of patient rooms, their heads, including isolation rooms. I must be out of my bloody mind sticking the probes in my mouth!

Dinosaurs/ Hens... Velociraptor with an accent on the Raptor. "Fast Bird Of Prey"

 

[KJ6EAD]

See http://en.wikipedia.org/wiki/Transcranial_direct-current_stimulation
The electrodes are prepared with saline solution and the skin at the contact area is prepared with "electrode cream".

Why does the term "electrode cream" make me giggle?

You're such a child. This is a serious forum for serious people to discuss serious things.

Even with the aforementioned preparations, the tiny current's just going to flow in the scalp making the treatment safe but ineffective.

And do not say anything about applying the electrodes with a nail gun!

I got 12 options when I looked for 5mA fuses at Digikey. Most were micros like this:

You can't see it but there's a tiny fuse wire half an atom thick between the leads.

 

[CDRIVE]

I got 12 options when I looked for 5mA fuses at Digikey. Most were micros like this:

You can't see it but there's a tiny fuse wire half an atom thick between the leads.

Ha, like I said, I have no patience with the DK search engine. You apparently have managed to master it. How much does this little jewel cost?

Chris

Edit: What's the nominal resistance? I would imagine a 5mA fuse would be measurable.

 

[KJ6EAD]

Around $25 each. They're probably laser trimmed to perfection. That doesn't come cheap especially when you're cutting atoms in half.

 

[CDRIVE]

Around $25 each. They're probably laser trimmed to perfection. That doesn't come cheap especially when you're cutting atoms in half.

I can't say that I'm surprised.

 

[KrisBlueNZ]

Even with the aforementioned preparations, the tiny current's just going to flow in the scalp making the treatment safe but ineffective.

I tend to agree about "ineffective". I got the same impression reading the Wikipedia page. It sounds like pseudoscience to me, but it's hard to be sure.

I got 12 options when I looked for 5mA fuses at Digikey.

That's pretty cool! I checked out the data sheet for the Littelfuse series, at http://www.littelfuse.com/data/en/Data_Sheets/272_273.pdf and they go down to 2 mA! Nominal resistance is 2200 ohms for the 2 mA fuse and 280 ohms for the 5 mA one. Wow!

 

[CDRIVE]

That's pretty cool! I checked out the data sheet for the Littelfuse series, at http://www.littelfuse.com/data/en/Data_Sheets/272_273.pdf and they go down to 2 mA! Nominal resistance is 2200 ohms for the 2 mA fuse and 280 ohms for the 5 mA one. Wow!

Ya just had to know the resistance of a fuse this sensitive was going to be high but I wasn't prepared for this. Wow!!

 

[Fer555]

Sorry to bother guys but i was also trying to do the same project as jjanes. This thread is great and helpful, but my knowledge is into these type of things is vague. Precisely what I am asking for help with is; I need more information about the parts used within the schematic for example the type of rotary switch used, the type of LEDs used, or the circled "A". I do not know what type of LED would be essential for it due to having to deal with so many choices. I however already know about the LM334Z. Thanks for any answer in advance.

 

[davenn]

hi Fer555
welcome to the forums

a 2 pole 5 way rotary switch

any typical (standard) 5mm diameter red or green LED
A in the circle is an Ammeter, only needs one that reads to ~ 50mA ( milli Amp)

cheers
Dave

 

[CDRIVE]

I had no idea there was so many people wanting to play Electrotherapist.