Miniature Digital Voltmeter/Multimeter

[IndustrialAction]

Hey guys, I'm working on a mod and need to tap into the vast resources here. I want to integrate a mini digital voltmeter into the mod. That part is easy. The part that I haven't quite figured out is how to get it to read/display resistance also. I've done the Google search thing but haven't found any candidates. Any thoughts/advice?

 

[Dave_uk]

Any thoughts/advice?

Yes, but you wont like them... lol

The first thing you have to accept is that an ohm meter is not real.... all it is is a different use of a volt meter.

So using ohms law we know that when applying a constant voltage to a circuit, as the resistance of that circuit rises or falls .... then the current flowing through that circuit will fall and rise.

If we put a fixed resistance in between the constant voltage and the circuit... then as the resistance of the circuit rises and falls the current through the fixed resistance will vary ... so remembering ohms law again, its an easy job to measure the voltage across the fixed resistance,
more current = more volts will be seen across the fixed resistor = lower circuit resistance

As we know the value of the fixed resistor and the voltage, its not hard to calculate the total circuit current and thus the resistance of the circuit (atomiser).

Now before we can turn the voltage measured into something useful, we have a few big problems..... the first one is

Calibration ...

The atomisers need to be measured to an accuracy of .1 of an ohm for the reading to be of any use, now as we know ... as the voltage used to supply the circuit (atomiser) varies, so will the current and so will the voltage measurement across our fixed resistance, so unless you intend to use a separate stable power supply and also incorporate a method of 'zeroing' then its a bit of a pointless exercise.

This is such a big problem that its not worth going onto the other issues.

However having said that, anything can be done..... if you throw enough circuitry at it ..lol

You could look at

http://freecircuitdiagram.com/2008/08/21/using-current-source-to-make-linear-scale-analog-ohm-meter/

And modify the circuit to suit your purpose ..

Then just replace the analogue meter with a resistor and use your digital volt meter to measure the voltage across it

 

[breaktru]

I am also looking for a tiny LCD or LED display like the one used in the ProVari. Check your PM I.A.

 

[IndustrialAction]

Dave, thanks for the good advice!

How do devices like the ProVari measure resistance? Is it delivering 3.7V when it takes the reading regardless of what the device is set to? What about Darwin? According to the material we've seen, Darwin constantly measures resistance changes and varies the voltage to ensure that the wattage stays constant.

 

[breaktru]

Not sure I.A. Maybe They get the resistance by calculating the voltage, amperage, wattage as I did in my PV Tune function shown Here:

 

[Java_Az]

Pretty sure the provari doesnt measure resistance it is just a variable voltage device. The darwin might but i think it more likely it measures the voltage and amps to give a constant wattage.

I have looked high and low for a small meter that does more then just the voltage. Madvapes is now selling the li po voltage meter thats the only one i know of that fairly small. But it just does voltage, no amp or resistance. Unfortunately I have come to the conclusion that if i want a really small meter that does more then just voltage i will have to design the circuit and build it myself. Which at some point i think i might just end up doing. The LED display is just one part to these things they need a led Driver IC chip or two and a properly designed circuit to work.

 

[IndustrialAction]

Nope, here are the functions of a ProVari...
Pu - Power Up
Pd - Power Down
Po - Power On/Off
Cb - Check Battery Level
Ao - Atomizer Resistance
Lo - LED On/Off

When it checks resistance and battery level, it delivers current to the atomizer (you can hear it sizzle). I'm wondering how much it is delivering.

 

[IndustrialAction]

Not sure I.A. Maybe They get the resistance by calculating the voltage, amperage, wattage as I did in my PV Tune function shown Here:

The calculation is easy. I use a free ohm's law calculator on my iPhone all the time. I don't want the display to do what Darwin is doing, just simply read/display atty resistance and voltage setting on my mod like the ProVari does. I wish had an EE background!

 

[Java_Az]

Didnt realize the provari checked resistance, thats pretty cool. It for sure has a programmed smart chip to do all that. Not something your going to find and buy off the shelf . Never too late to start learning. Other then that i guess you could hire a EE to design one for you.

 

[IndustrialAction]

Didnt realize the provari checked resistance, thats pretty cool. It for sure has a programmed smart chip to do all that. Not something your going to find and buy off the shelf . Never too late to start learning. Other then that i guess you could hire a EE to design one for you.

I thought about sending in my specs and having one made but then I realized that I get way too wrapped up in these things, ha-ha!

Maybe I'll cut-up my ProVari and stick it's guts in the mod. Jk!!

All of these new devices are really cool but I'm starting to think that they're moving us away from the important thing, namely, taste. At the end of the day, all that matters is that we have an enjoyable vaping experience. For my mod, I'm just going to stick with a thumb-wheel voltage adjustment from .1V to 8V and no meters. That way I'm not distracted by numbers that are, quite frankly, inconsequential to my taste-buds.

 

[Java_Az]

I agree with you there. You can have all kinds of fancy stuff on the PV But if it is not user friendy then whats the point. The mod i am working is designed with taste buds in mind. No calculators or math to do. Real time adjustable voltage and let your taste buds decide the proper voltage to use for what ever atomizer or cartomizer you slap on it.

 

[IndustrialAction]

Yeah, I didn't want to let the cat out of the bag too early on mine until I get it in my hands. It is out for paint/graphics now. Since I'm eliminating the meter/display, it will let things come together quicker. If you want to compare specs, here's what I've got so far...

Variable voltage (thumb-wheel adjustments from .1v to 8v)
6000 mAh internal battery pack
USB passthrough capable
USB external charging capable
Hard on/off/charging switch
Battery level display
A few surprises (have to see how they work out first...)

 

[breaktru]

Yeah, I didn't want to let the cat out of the bag too early on mine until I get it in my hands. It is out for paint/graphics now. Since I'm eliminating the meter/display, it will let things come together quicker. If you want to compare specs, here's what I've got so far...

Variable voltage (thumb-wheel adjustments from .1v to 8v)
6000 mAh internal battery pack
USB passthrough capable
USB external charging capable
Hard on/off/charging switch
Battery level display
A few surprises (have to see how they work out first...)

Sounds great I.A. I am in the process of eliminating my trimmer pot. I have a digital pot setup on a bread board w/ the 4050 regulator and a small digital meter. Just deciding what to put it in.

 

[breaktru]

Pretty sure the provari doesnt measure resistance it is just a variable voltage device. The darwin might but i think it more likely it measures the voltage and amps to give a constant wattage.

I have looked high and low for a small meter that does more then just the voltage. Madvapes is now selling the li po voltage meter thats the only one i know of that fairly small. But it just does voltage, no amp or resistance. Unfortunately I have come to the conclusion that if i want a really small meter that does more then just voltage i will have to design the circuit and build it myself. Which at some point i think i might just end up doing. The LED display is just one part to these things they need a led Driver IC chip or two and a properly designed circuit to work.

Hey Java, I already have a small D.M. like the one that Madvapes has. I was looking for a smaller display about half that size. Even if it's just for voltage. Something that can fit in my Copper Mod w/ 18350's.

 

[asdaq]

Something digital thermometer sized, less than 12v and fairly cheap would be great. Too bad it seems to not exist.

 

[breaktru]

I know asdaq, I've searched for weeks. Guess it is custom made

 

[IndustrialAction]

I'm sure the Chinese could make them for 1,000 piece minimum order. LMAO!

 

[asdaq]

Miniature analog would be grand too, if small enough and somewhat accurate. I'd even settle for a strip of 10 LED's preset with _insert proper component_ to light up provided voltage is high enough.

 

[Java_Az]

Yeah, I didn't want to let the cat out of the bag too early on mine until I get it in my hands. It is out for paint/graphics now. Since I'm eliminating the meter/display, it will let things come together quicker. If you want to compare specs, here's what I've got so far...

Variable voltage (thumb-wheel adjustments from .1v to 8v)
6000 mAh internal battery pack
USB passthrough capable
USB external charging capable
Hard on/off/charging switch
Battery level display
A few surprises (have to see how they work out first...)

Sounds pretty awesome. I am trying to keep my cat in the bag till i get it done anyways. Almost there i hope, this is taking way longer then i though it would. Maybe this weekend I will have it done. My digikey order shipped today so i hope it gets here by friday. Not too big a deal i have some mechanical stuff that needs to be done. I should be on my lathe right now instead of the computer.

Hey Java, I already have a small D.M. like the one that Madvapes has. I was looking for a smaller display about half that size. Even if it's just for voltage. Something that can fit in my Copper Mod w/ 18350's.

If there is one out there i sure haven't found it. Bad thing is the meters i have they sand the serial numbers off the chips. Makes it harder to locate a chip that will run a meter. The ones i found free circuits to on the net are pretty large chips. When i get my mod done i will look into it some more and design one from scratch.

 

[AttyPops]

Good luck with the new mod. Sound ambitious. We've had some limited discussions on MCU's and smart e-cigs (like for the atty resistance measurement and watts auto adjust). For reference see:

http://www.e-cigarette-forum.com/fo...want-mod-super-powers-picaxe.html#post2516778
http://www.e-cigarette-forum.com/fo...nyone-built-pwm-style-vv-mod.html#post2484280
http://www.e-cigarette-forum.com/forum/battery-mods/149538-digital-potentiometer.html#post2404772

to get you started. The resistance measurement mentioned above might be strait forward with the Analog-to-digital converter on-chip. Usually used to read a POT, but can be used to read an atty. Not sure how sensitive it is tho. May require some kind of special circuit to get down to fraction-of-an-ohm levels. Reading 100 ohm vs 250 K ohm or anywhere in between is a lot different than, say, 1.5 ohms vs 3.0 ohms.

Also, I suggest color coding or numbering the thumb wheel. It's a real strait forward way to get vv controls without all the PITA display stuff (unnecessary IMHO).

They also have discussions on PWM power management, if you use an MCU.

OTOH, everything you are talking about in your latest post doesn't require an MCU, other than possibly the unknowns/surprises. Remember K.I.S.S. lol.

Hope you have loads of fun and get a neat PV out of this.