I should add that the net energy equation will always balance so my use of the word efficency should be taken in the context of efficency for this application.
My First Pulse Width Modulator Mod
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I should add that the net energy equation will always balance so my use of the word efficency should be taken in the context of efficency for this application.
One other consideration is that higher frequencies increase electrical losses. As already mentioned, you want a frequency high enough to surpass the thermal conductance of the heating element, but not so high as to reduce efficiency. MOSFETs can actually have a considerable amount of capacitance. That's why FET selection is critical for high frequency switching regulators. You typically use parts specifically designed for that application. So, running a higher frequency in the tens of KHz range, for example, would probably not be of any benefit.
I never thought of that! It's true that, with a PWM, which is an AC device, the coil of the atty itself becomes an air coil inductor or choke, adding much more resistance (or I should say inductance) to the circuit. As it heats up, the inductor will vary in resistance. See, you guys are gods of modding, I'm just a tinkerer 
The design of the atty itself, the spacing between windings, the ga of the nichrome wire, everything adds another layer of complexity. So I guess every different atty or carto will act differently. It's almost more than vI can wrap my head around. I'm thinking that the Darwin, as ugly as it is, may be on the right track, it self-adjusts to the load.
I am in awe!
The design of the atty itself, the spacing between windings, the ga of the nichrome wire, everything adds another layer of complexity. So I guess every different atty or carto will act differently. It's almost more than vI can wrap my head around. I'm thinking that the Darwin, as ugly as it is, may be on the right track, it self-adjusts to the load.
I am in awe!
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Hehe, don't blow a gasket over it. Lower frequencies can be pretty much treated like DC as far as parasitic characteristics (side effects like the inductance of an atomizer coil). For most circuits, you don't have to really start considering it until you get into the hundreds of KHz. So, for our purposes, you can neglect all that stuff. Things remain fairly simple when limited to DC. AC is where things get really involved and the high frequency stuff is where it gets crazy.
I'm not sure how accurate the Oscope display is on that emulator but that circuit is giving you variable frequency/pulse width. The only constant in that circuit is the off duration. What we want is exactly the opposite where the off cycle is what is being varied. It may work but I don't think it will reduce the Vrms very far. If you slide the resistance slider while watching the wave form you will see what I mean. The off cycle should get longer as the resistance is lowered instead of decreasing the on cycle. A little confusing the way it's worded but run the resistance slider back and forth a couple of times and you will see what I mean.
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Here is a picture of what I mean. This is a little simplistic but I think it conveys what I mean.
The first trace is of a constant frequency pulse with 50% duty cycle
The second trace is what that circuit is doing. It has a constant off time which until you get down to the bottom of the scale will have little effect on Vrms
With this one the time of one off cycle and one on cycle combined is not constant which means variable frequency.
The third trace is a PWM circuit with the off time being varied
With this one if you add an on cycle and trailing off cycle the time is the same all the way across meaning constant frequency.
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OOps meant to quote this comment in my previous post.
anyway I think you would get a logarithmic scale instead of a linear scale for the duty cycle. All in all it would probably work and based on how much I have to turn mine up as the battery drops off I am wondering if that is what mine is doing. I might have to get that sound card Oscope setup to see what it is doing.
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His circuit should work as long as he isn't bothered by the freq change. The varying frequency is just the nature of the beast with the 555.
If anyone is interested in a cheap scope, Parallax has a 200khz USB unit that they are closing out for $149. 200khz is slow, but it works for this kind of stuff. It's a 2 channel digital storage with a single external trigger.
If anyone is interested in a cheap scope, Parallax has a 200khz USB unit that they are closing out for $149. 200khz is slow, but it works for this kind of stuff. It's a 2 channel digital storage with a single external trigger.
200KHz would be a little low. For general purpose stuff, 20MHz would be about the lowest bandwidth you'd want. However, digital storage is a big plus and may make it worthwhile if you're sure you'll never want look at anything with a period less than a few µseconds. Though if you're planning to do anything with µcontrollers, for sure you'll want at least a 20MHz scope.
My recommendation would be to buy a 2nd hand analog scope off eBay. There's tons of them and I've seen name brand names with bandwidth as high as 100MHz sell for as little as $50. Digital storage is great, but it means $$$ and you can get by without it a lot of the time, especially if it's your first real oscilloscope. You'll spend enough time just learning how to use and read it, let alone storing anything.
My recommendation would be to buy a 2nd hand analog scope off eBay. There's tons of them and I've seen name brand names with bandwidth as high as 100MHz sell for as little as $50. Digital storage is great, but it means $$$ and you can get by without it a lot of the time, especially if it's your first real oscilloscope. You'll spend enough time just learning how to use and read it, let alone storing anything.
Missed it .. is this the PC scope freeware program, that uses your sound card input, of which you speak? It's true, it is limited to the capabilities of the soundcar (44Khz), but for free it looks promising.
http://www.electronics-lab.com/downloads/pc/002/index.html
http://www.electronics-lab.com/downloads/pc/002/index.html
For you breadboarders out there, check out this tiny oscilloscope Xprotolab 
Mine arrived today, I can't wait to play with it. For $50, it has a ton of features. It has enough features for most of my projects and all of my ecig projects.
I wish you could buy spare time on the internet. That's what I really need lately
Mine arrived today, I can't wait to play with it. For $50, it has a ton of features. It has enough features for most of my projects and all of my ecig projects.
I wish you could buy spare time on the internet. That's what I really need lately
That's true, the juice gets really hot if the power driving the atty remains constant. If we just reduce the duty cycle with the vape time, we can adjust the atty temperature at a constant value. The best rate for duty cycle drop can be adjusted by trial and error.
I think it would be difficult to find a proper frequency, because the heating/cool down freq would depend on the amount of juice in the reservoir, air flow rate, and other parameters (on a second thought, it might not. I'm not sure??). A trial and error might work here also. But if we just concentrate on the rms value of the power, we should be ok. Of course this would be a linear control system. I'd like to see someone doing a PID control or a closed loop system
That's true, the juice gets really hot if the power driving the atty remains constant. If we just reduce the duty cycle with the vape time, we can adjust the atty temperature at a constant value. The best rate for duty cycle drop can be adjusted by trial and error.
I think it would be difficult to find a proper frequency, because the heating/cool down freq would depend on the amount of juice in the reservoir, air flow rate, and other parameters (on a second thought, it might not. I'm not sure??). A trial and error might work here also. But if we just concentrate on the rms value of the power, we should be ok. Of course this would be a linear control system. I'd like to see someone doing a PID control or a closed loop system
I thought about doing a closed looped system but I don't think I can get enough resolution measuring the resistance across the coil considering the low ohms and the low tempurature coefficient of nichrome. Maybe I'm not giving modern ADCs enough credit.
External temp monitoring is an option that might work. I saw somewhere on the net where a guy was using a capacitor bank to .... weld dissimilar metals to form thermocouples. if we could slip an axial thermocouple through the center of the wick it may give enough reference to do it.
In any case the method you are describing is probably a great place to start. If I make the ramp linear it could be as simple as a loop using three variables. A state counter to adjust the length of time for inital full power, a decrement variable to adjust the ramp rate, and a bottom cap variable to adjust the range. I'm hoping to wrap up a project next week and finally get some time to put some things together.
Ok, Now I am wondering what the response time of a simple thermistor would be, and if we put that in line with the POT of the simple PWM circuit.... Just take the cartos temp the old fashion way =] Too bad it would probably kill the airflow.
Now I'm thinking SGV3 / PWM mod....
Now I'm thinking SGV3 / PWM mod....
I finally got the board successfully crammed into a NoEgo. It is working very well so far. I had to forgo the lever adjust and just stick a small screw driver into a hole. Works as good as it did in the box and is easier to hang onto. I am loving it so far. Of course my hole wasn't perfectly centered so I have fish around in there a little bit to find the slot on the POT.
I didn't snap any pics because it looks stock except for a hole opposite the switch.
I'm going to do a second but I will have to make a homade back plate because the bodies I have, have the counter sunk openings and don't give enough room. So i'm just going to make a circle cutout of some circuit board. This will have the advantage of soldering much easier.
I'm still trying to find something to use as a knob to attach to the POT. I couldn't do it on this one because the hole didn't line up good enough.
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I think I have everything needed in the parts bin. Just been busy with the SGV3 co-op...
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