I am on my second and more advanced version of an energy stick for my elementary level science electronics class. The first version is working well. I have provided a schematic. I want to use this circuit with two 2N2222s to switch an IRLZ44 that will turn on a 9-12V LED powered by a Lipo 3.7V battery and a booster so I have enough power for the larger LED. I have built several versions on the breadboard but the LED switches on when I touch only one end of the energy stick. I have put in a number of different pull-down resistors but I haven't been able to find a balance of the right resistors in the right place to turn the high powered LED on only when a circuit is completed. Just now it turns on like a touch switch.

I have included the schematic of the original version and the new high powered LED version. The original works nicely and is exceptionally sensitive but won't turn on when holding only one end. I am stuck on the new version as the LED flashes on when touching only one end.

 

You have told us what it does wrong but you didn't explain how it is supposed to work.
Regards,
Keith

 

Can you provide a schematic? Some of the connections you show don't seem to make sense, a schematic will help. Are you sure it is wired according to the schematic?

 

It would help if you explained what an "energy stick" is and what it is supposed to do. I've never heard of it until now and had to go Google it -- don't expect people that you are asking for free help from to make that effort.

It would also help to provide an actual schematic. The drawing you have doesn't even indicate which pins are what on the two transistors. Don't make people assume or guess. Also, we have no idea what the circuit board is going, so it's going be very hard to tell you how to get things to do what you want. Is the board needed for the thing to work at all, or can the LED light up if the board is removed and the output wires tied directly to the battery?

Explain the theory of operation behind your approach -- how does connecting the two ends by a very, very high resistance connection result in operation?

I would think that FETs would be better choices.

[RANT]
When I went to see if I could find a circuit schematic for an energy stick, I observed something that is not too reassuring. I found links for "how does an energy stick work" and not one of them (that I looked at) explained anything about how an energy stick works beyond "connect both ends with some kind of conductor and it lights up and makes sound". One was even a video where the guy breaks open the plastic tube, points to a wire connected to the metal tabs and then points to a circuit board and that's it -- end of video. When I looked up "how to make an energy stick" I got links about DIY energy sticks and all of them were nothing except pictures of commercial energy sticks. I guess the detailed steps would have been something like: (1) Buy energy stick, (2) Open package. You've now "made" an energy stick.

I was in Barnes and Noble last week and was looking at their STEM educational kits. They had one that was an FM radio and said on the outside that you would learn how an FM radio works. But the kit consisted of a potentiometer, some wire, a speaker, a battery holder, and a circuit board with a blob of epoxy over the middle of it. Yep -- gonna really learn a lot from that hand-on project.

What are we coming to?

I guess I shouldn't be too surprised when some math books "teach" exponentials and logarithms by showing pictures of which button to press on a calculator when you see one in a formula.
[/RANT]

This rant is NOT aimed at you -- I applaud what you are trying to do.

 

off topic,
But how do you manage to teach the "darlings" not to try this on a mains socket ?
( I used to show a van de graph gen, with the kids hair standing on end, till one kid went home and tried it on the mains .. )
no matter what you say , teach, some "darling" will find a way.

 

These are my interpretations of the schematics from your pictures.
I have not show the BMS module as it's only function is to protect the cell.
Are these schematics what you intended them to be ? Like the others I had no idea what an "energy stick" did. After drawing the schematics it looks like it is just a continuity tester that show continuity even with quite a high resistance between the ends. The actual value will depend very much on the hfe of the transistors. The old circuit has the potential of destroying the transistors if the resistance between the two ends is quite low as the input transistor will be close to saturation shorting the 3.7 volt supply across the base emitter junction of the second transistor.
I think the new circuit is switching on when only one probe is touched is due to pickup of radiated switching frequency from the boost regulator. You may have to screen the boost regulator and put filtering on it's input and output connections. I suggest first supplying the high voltage output from another battery rather than the step up regulator to test if my theory is correct. The new circuit may need something to limit the LED current. (Unless it has built in current limiting.)

NOTE. I have used the pinout information from the 2N2222 data sheet. The collector and emitter pins seem to be the opposite way round to most TO92 transistors.

Les

 

These are my interpretations of the schematics from your pictures.
View attachment 215143I have not show the BMS module as it's only function is to protect the cell.
Are these schematics what you intended them to be ? Like the others I had no idea what an "energy stick" did. After drawing the schematics it looks like it is just a continuity tester that show continuity even with quite a high resistance between the ends. The actual value will depend very much on the hfe of the transistors. The old circuit has the potential of destroying the transistors if the resistance between the two ends is quite low as the input transistor will be close to saturation shorting the 3.7 volt supply across the base emitter junction of the second transistor.
I think the new circuit is switching on when only one probe is touched is due to pickup of radiated switching frequency from the boost regulator. You may have to screen the boost regulator and put filtering on it's input and output connections. I suggest first supplying the high voltage output from another battery rather than the step up regulator to test if my theory is correct. The new circuit may need something to limit the LED current. (Unless it has built in current limiting.)

NOTE. I have used the pinout information from the 2N2222 data sheet. The collector and emitter pins seem to be the opposite way round to most TO92 transistors.

Les

Thank you Les.
You have managed to understand my thinking very well and that drawing is excellent. It is what I was thinking but wasn't able to get it on paper like you have. The "Energy Stick" is basically a continuity tester for lack of terminology to describe it. I see now that I am not the only one that doesn't understand the term "Energy Stick" although Google was pretty good and pulling up information on it except for a schematic on how to make one. My aim is to use it in teaching English and simple circuits. Sometimes it can be confusing for Non-native English speakers when talking about open circuits, closed circuits, short circuits, on/off etc especially when children use "on" and "open" to mean the same thing in their own language. So it is my intention to teach using hands-on - literally standing in a circle holding hands to close the circuit and turn on the LED. I don't want the buzzer or speaker as they do in the commercial units.

My theory behind what I think the operation should be is that when there is a very slight flow of current through the circuit (of children holding hands) it is sufficient to turn the 2N2222 BJT on and then the LED. Using just one BJT wasn't sufficient so I made a Darlington Pair to increase the current gain. My thinking is that the 2N2222 BJT won't stand 0.66A current which I want through the High Powered LED so the next best thing in my toolbox is the Mosfet.

Les, I will put your circuit together as soon as I get a chance and let you know how it goes. I think it looks great.

This is my previous finished product: The battery and wires are in the PVC pipe. It works by making a circuit by touching it either with one hand or two separate hands or even with 20 people in a circle holding hands. It will also turn on if two people hold it without holding hands but both participants are standing on a tiled floor not wearing shoes.

 

the human body DC resistance is about 1..2MΩ but depending of moisture and oiliness it may come down to 3kΩ and go up to above 10MΩ
in othwer words your continuity should apply for about 2kΩ ... 20MΩ "test sample"

we can assume the ~AC impedance of the body is a lot lower - so , about using human as a wave guide.. (if you're not to test anything else) ..is likely a better idea

( with a high gain amp you can likely test only the 1 point connection e.g. a human-antenna input -- i don't have the input frequency voltage specs for such however)

 

Energy Stick appears to be what used to be called "Love Meters" and similar. All it does is sense skin/body resistance across the two electrodes. In other words, a conductivity meter.

https://kidminscience.com/product/energy-stick/

 

off topic,
But how do you manage to teach the "darlings" not to try this on a mains socket ?
( I used to show a van de graph gen, with the kids hair standing on end, till one kid went home and tried it on the mains .. )
no matter what you say , teach, some "darling" will find a way.

It isn't really something that they can put into a socket - It takes every bit of effort to get them to even touch it. I guess I am in a different part of the world where things come together a bit differently.

 

the human body DC resistance is about 1..2MΩ but depending of moisture and oiliness it may come down to 3kΩ and go up to above 10MΩ
in othwer words your continuity should apply for about 2kΩ ... 20MΩ "test sample"

we can assume the ~AC impedance of the body is a lot lower - so , about using human as a wave guide.. (if you're not to test anything else) ..is likely a better idea

( with a high gain amp you can likely test only the 1 point connection e.g. a human-antenna input -- i don't have the input frequency voltage specs for such however)

Interesting... I will run some tests with my resistors and see what works and what doesn't. With my old unit, the red LED comes on first so it is a good indicator of the type of connection in the circuit on children holding hands but usually, just a simple contact of two little fingers will be enough to turn both LEDs on. Making the circuit through the tiles on the floor is more tricky. With one toe, no socks, down, there is a slight glow in the red LED. Putting more toes down will slowly brighten the red LED and then both LEDs come on. I imagine that the resistance through ceramic tiles on the floor would be greater than human body resistance when the floor is dry.

 

Connecting a capacitor (I would suggest about 100 nF.) in parallel with R6 in your modified circuit may solve the problem.
Here is a simpler version using your IRLZ44 mosfet.


The 12 volt zener diode and 47K resistor is to protect the mosfet. It limits the gate source voltage to between + 12 volts and -0.7 volts. I have added the 100 nF capacitor as this circuit may also have the problem with high frequency noise from the boost converter. Sorry about the hand drawn circuit but I find it quicker than using Eagle PCB software to draw circuits.

 

device ident :
https://www.addicore.com/TP4056-Charger-and-Protection-Module-p/ad310.htm Li-Ion Charge/Discharge Controller ( outp 3.7V )
https://components101.com/modules/xl6009-dc-dc-step-down-voltage-regulator-module ( outp 5 - 35V (adjustable) )
if someone wants to debug these circuits ...

? why the high light-power LED (it's dangerous to watch these close by) . . . ? for a "distant" class presentation
... you likely want to add a "range" switch -- near max power for distant show and a barely visible for a hands on trial

 

With one toe, no socks, down, there is a slight glow in the red LED. Putting more toes down ...

your age?
and NE coordinates the 200km error allowed? (i will attempt to scan the anomalies at the area ... the success would be quite unlikely but ńot impossible )
run a self check -- literally -- are you running you yourself ? or you've been overtaken by unknown spirits ?

// i'm just telling what such sound from far away without background data

————————————————————————————

the options that credit the particular showcase as "normal"
(the line is where you draw it ... there's no one else knowing where it should be ...)

• the age group you are teaching is below the 10 ... 11 yo (year old)
• you're home schooler
• you live in a small society where everyone knows everione
• you've had that class from the begining
• the showcase you figured out gives a WOW effect
  // the public awareness of physics is ... inexistent
  // if you can come up anything that may trigger their motivation to learn more about the subject - the weirdness of the experiment likely fall to a secondary option
• you name it ...

people are also unaware of "normal" = if your class thinks your strange you may loose your prestige ... worse - it may take one "schizo" parent to complain for you to loose your job ?

————————————————————————————

the toe magic likely addresses to polarization and surface charge of the dielectric - that combined with the 400kHz disturbance from the DC/DC booster

if there's space between the floor and foot - there's a high impedance capacitive barrier - if there's a direct contact at "significant" surface area that affects the inside polarization of the dielectric (floor) tied to the surface charge of the entire floor

. . . it much likely won't work with a steady 12V battery in place of the DC/DC conveter

***

 

LED brightness adjust

 

device ident :
https://www.addicore.com/TP4056-Charger-and-Protection-Module-p/ad310.htm Li-Ion Charge/Discharge Controller ( outp 3.7V )
https://components101.com/modules/xl6009-dc-dc-step-down-voltage-regulator-module ( outp 5 - 35V (adjustable) )
if someone wants to debug these circuits ...

? why the high light-power LED (it's dangerous to watch these close by) . . . ? for a "distant" class presentation
... you likely want to add a "range" switch -- near max power for distant show and a barely visible for a hands on trial

The LED will be in a tube with a diffusion type coating on it rather than in a clear tube.
There will be activities both indoors and outdoors and the little LEDs just don't pack enough punch in some conditions but I see your point. Since I have a great little one for small classes, my next version will be for a larger and outdoor class.
Thanks

 

Instead of a diffuser, if it is in a sealed tube, you can add a fluorescent dye solution. That will make the whole tube light brightly. Two common dyes are fluorescein (green yellow) and rhodamine B (red). You have probably seen fluorescein. It is used for leak testing and may be what is added to automotive antifreeze.

 

if Your LED draws high power - it gets hot
for the led to have high power (through the step up converter) the Li cell needs to provide even more power
depending the amount of the "even more power" the battery may get hot
the particular Li-ion controller does not have a temperature sensing function

the way the device is used likely gives it reasonable cooling time ... but maybe not ... or if it's left on a conductive surface

simple solution : limit your LED current/power to be in accordance with the Li-ion datasheet
but the datasheet - if one exists - may not give you time and ambient related safe operating conditions ...

complex solution : heat sink your led + thermal monitor protect your Li-Ion cell

 

if Your LED draws high power - it gets hot
for the led to have high power (through the step up converter) the Li cell needs to provide even more power
depending the amount of the "even more power" the battery may get hot
the particular Li-ion controller does not have a temperature sensing function

the way the device is used likely gives it reasonable cooling time ... but maybe not ... or if it's left on a conductive surface

simple solution : limit your LED current/power to be in accordance with the Li-ion datasheet
but the datasheet - if one exists - may not give you time and ambient related safe operating conditions ...

complex solution : heat sink your led + thermal monitor protect your Li-Ion cell

It is true that I anticipate the LED would only be on for 10 to 20 seconds at a time but there would also be countless occasions that I wouldn't have control over that. I better play it safe. I will limit the current - Attached is my battery.

I have a tiny Al heatsink I can use for the LED but it will be enclosed in a pretty small space so I imagine it will only help for a few moments. I will try a human-touch thermal monitor prior to installing everything in the tube and then hope for the best.

Thanks for this advice.

 

I imagine it will only help for a few moments

it depends how much time you are willing to spend on the design process . . .the heat fades away from unit surface source with square root dependency if your outer casing has the surface area of A and your led junction (double sided) has a total surface area of α then a theoretical the outer casing temperature would be α:A·Tj
... say 1mm² : (200·π·17mm²) · (150-20)°C -- if the thermal resistance from case to ambient would be "0"

since it's not you may try a double shell design with the free air movement space in between

if there is a requirement for such - i can't imagine your app.-s real life power dissipation

the heat sink just helps to draw the LED's junction lower ... it's better to be there than without