Miniature Digital Voltmeter/Multimeter

[IndustrialAction]

You're good in my book, Tony.

I created this topic in hopes of finding a solution for a mod I'm working on. Because I own a ProVari and respect what Darwin does (even if I despise the device itself), I wanted to at least have the ability to read/display voltage and resistance on my mod. However, over the relatively short evolution of this thread, I came to the personal realization that in my mod, the display isn't necessary. Yes, it is cool. Yes, it is being done and more mods will feature it. But no, it isn't as important to me anymore. In-fact, it went from the top of my wishlist to not even being on the list.

The reason is purely personal and it stems a lot from things Atty and the others have said. At the end of the day, the most important thing to me is that I can dial-in my voltage to adjust the mod to suit my taste for whatever liquid/atty combo I'm using. My tastebuds can't read a display. They don't care what the numbers are. Besides, the mod will have a sufficiently cool appearance on it's own without the display.

 

[DaveP]

I like the aesthetic value of the digital readout for voltage, but a bar graph type display would be just as useful. If you know the range is 3.3 - 6vdc, then a simple voltage driven mini s-meter would do the trick and let you know at a glance where you are. It could be triggered through a gate only when the button or thumb wheel potentiometer is used.

 

[CraigHB]

This is an old thread, but it's the first time I've seen it and would like to comment on the question the OP had (though he's probably moved on by now).

There's two ways to get a resistance reading off an atomizer. One is to measure the current drawn by the atomizer while energized then simply divide into the known voltage. The other is to quickly measure resistance when the atomizer is de-energized using a low voltage current source, basically an ohmmeter. I don't know for sure, but my guess is that the Darwin uses the first method I mentioned. It would have to measure current in order to precisely regulate wattage. The Pro-Vari probably uses the second method since I don't believe it measures atomizer current outright.

Employing resistance measurement in a home brew mod will require an MCU (micro-controller unit). There's no way around it. You need one to drive the display anyway.

The easiest way to do it is by measuring current. Other than an MCU, it requires only a current sense resistor in series with the atomizer on the low side and an op amp connected on either side of it in differential mode. The current sense resistor normally has a very small resistance (like 10mΩ) to minimize power loss. The voltage drop across it is going to be very small. The op amp is required to linearly boost the voltage signal to put it in the correct range for the MCU's ADC (analog to digital converter). The MCU reads the signal with it's ADC rendering a digital value. You do a little math in code to derive current from signal level then divide into voltage to get atty resistance. Relatively simple stuff as far as circuit design and MCU programming goes. One other benefit of this method is you can also display current and wattage as measured directly.

The more complicated method is to take a measurement similar to a DMM. That requires more circuitry. You're pretty much incorporating an ohmmeter into your mod. The advantage there is you don't need a current sense resistor (which gives up some power and thereby efficiency) and you don't need to energize the atty to get a reading. I've never built an ohmmeter myself or have I thought about it so I don't know exactly how much circuitry it involves, but I'm sure it's considerably more. In any case, it will boil down to a signal that needs to be digitally converted and computed by an MCU.

 

[wfx]

edit. going to start a new thread in battery mods for this one.