this project is exciting... wish I had some time to work on this with you. I think one of the issues you will have with the constant wattage control will be the shunt resistance required to measure current. Low ohm high watt resistors are large, higher ohm resistors limit current. I have a spec sheet for a digitally controlled analog switch, the current rating is low but if the Arduino has a D to A you could supply milivolts and switch on a low watt resistor in series.
An Absurd Experiment - The Digital Boy
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actually a current shunt can be low wattage.
A 10mv/amp shunt (0.01 ohm) is usable.
That would be 30mv for 3 amps, or about 90 milliwatts.
A/D resolution of 2000 counts (3 1/2 digit) with a full scale 30mv would be adequate to
resolve 1.5 ma.
Good shunts usually don't drop a lot of voltage.
The ones in cheaper meters, oh well.
For example, a little over an inch of atty heater wire can be 3 ohms, and take a couple of amps. A little heavier wire (with a lower temperature coefficient of course) could serve as a shunt.
Rocket
A 10mv/amp shunt (0.01 ohm) is usable.
That would be 30mv for 3 amps, or about 90 milliwatts.
A/D resolution of 2000 counts (3 1/2 digit) with a full scale 30mv would be adequate to
resolve 1.5 ma.
Good shunts usually don't drop a lot of voltage.
The ones in cheaper meters, oh well.
For example, a little over an inch of atty heater wire can be 3 ohms, and take a couple of amps. A little heavier wire (with a lower temperature coefficient of course) could serve as a shunt.
Rocket
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So this is the sort of circuit I'd need, correct?
Would this part be sufficient for a shunt? It's pretty big, but I can't find anything smaller with a 1% tolerance. The Arduino only has 10bit resolution (1024 steps) on the 5V analog inputs. That's not much resolution at the range we're measuring here. I'm thinking an opamp might be in order.
Code:
Vout
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---- Volt measure
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z
z Atty
z
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---- Amp measure
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z
z .01ohm shunt
z
|
_
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GroundWould this part be sufficient for a shunt? It's pretty big, but I can't find anything smaller with a 1% tolerance. The Arduino only has 10bit resolution (1024 steps) on the 5V analog inputs. That's not much resolution at the range we're measuring here. I'm thinking an opamp might be in order.
I really love the direction this mod is going variable power to the atty controlled by a sensor .One to control a pump that's great idea Peter . Imagine it,I have a request too can it tell you the liquid level of the juice bottle and the battery level. Open source would be enough for me to buy in to it for sure.
Dan
Dan
Battery level is easy and already built into the design. Piezo pumps are really expensive in the size you'd need to fit into a handheld mod. I don't know what kind of level sensor would work in a bottle that small, but I'm sure someone could come up with something. I'm not completely ruling it out, but I'm not going to look into it until the basics are ironed out. Besides, I use cartomizers more often than not, so juice delivery isn't really a problem for me 
But yes, the software will be open sourced if I ever manage to get it into releasable condition. Any functional schematics/board layouts will also be posted if/when they are ready.
But yes, the software will be open sourced if I ever manage to get it into releasable condition. Any functional schematics/board layouts will also be posted if/when they are ready.
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candre23
You rock dude.
I'm more of a mechanical kind of guy.
I have a cnc I built by hand, all the ballscrews and computer components .Wiring power supplies and all. The programming was the largest hurdle of all . Would love to learn how program chips and do more electronics but time is always an issue. But with you Maybe I can have a super high tech e-cig . Maybe I could cut you a nice box out for yours .Wood ,plastic, soft metal .something trade for a circuit made by you to fit a box made by me .Oh I cast Aluminum also . Think about it custom made one for you in trade lol tempting huh.
You rock dude.
I'm more of a mechanical kind of guy.
I have a cnc I built by hand, all the ballscrews and computer components .Wiring power supplies and all. The programming was the largest hurdle of all . Would love to learn how program chips and do more electronics but time is always an issue. But with you Maybe I can have a super high tech e-cig . Maybe I could cut you a nice box out for yours .Wood ,plastic, soft metal .something trade for a circuit made by you to fit a box made by me .Oh I cast Aluminum also . Think about it custom made one for you in trade lol tempting huh.
If I can actually pull this off, you have a deal. I already have some thoughts on how I would like it to look, but that's getting the cart before the horse. The brains have to be finished before I can worry about the body. I found this site which does one-off PCB printing for cheap. Once I've worked out the hardware on a breadboard I should be able to lay out a more elegant finished version in Eagle and have them make up a few. BatchPCB even lets you post your design so that others can order up a board directly from them. They let you sell them too, but I don't intend to do that.
I've been lurking the Arduino forums for the last week or so, and luckily they appear as helpful there as people are here. I know I'm going to need assistance with the programming. I installed/programmed HVAC control systems for several years, but they used a very simplified version of BASIC which is a hell of a lot easier to work with than the C-ish language of the Arduino. There is going to be a lot of trial and error with this. It will probably take me a couple months, and that's if I don't get distracted by other projects.
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I might be able to help with the programming. I'm currently working on my thesis and it includes an atmega128
Great! When I inevitably run into a stumbling block, I'll definitely post it here, as well as the Arduino forum. I can mostly follow the example code I've seen, but like I said, my only extensive programming experience is with a highly specialized version of BASIC, so there will definitely be some learning involved.
Candre23
I'm a patient man. I'm in no hurry ,I wont want you to be either . I would like the extras the chip, we could work out what you wanted also .Would work for boith of us .Caint wait to see the progress .
I'm a patient man. I'm in no hurry ,I wont want you to be either . I would like the extras the chip, we could work out what you wanted also .Would work for boith of us .Caint wait to see the progress .
Cadre,
What OS do you run?? do you have AVR studio and win avr yet?
In my experience they both run better on windows xp and you can use a USB to RS232 dongle, just make sure the port settings are correct.
If you haven't yet check out AVR Freaks
What OS do you run?? do you have AVR studio and win avr yet?
In my experience they both run better on windows xp and you can use a USB to RS232 dongle, just make sure the port settings are correct.
If you haven't yet check out AVR Freaks
I had planned to use the Arduino dev software, since it is specifically designed to work with the board I ordered, and that's what all the other Arduino devs use (any instructions they give me will make sense with my software). My board has a USB interface built-in, so once I get the driver installed, it should be pretty much plug-and-play.
nice, like I said I am using an AVR, a little different but the concepts are the same. I have noticed that people are porting win avr for Arduino chips so I thought you might be taking that route.
your 10 bit A/D with a 20X voltage gain opamp would give 25ma current resolution.
Control, with at least 1 bit of noise would be +/- 50ma, or sense a 2% change at an atty current at 2.5 amps, compensating for a resistance change of 0.04 ohms in a 2 ohm atty.
Control, with at least 1 bit of noise would be +/- 50ma, or sense a 2% change at an atty current at 2.5 amps, compensating for a resistance change of 0.04 ohms in a 2 ohm atty.
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That's pretty much what I was thinking. It seems like every couple posts in this thread adds more components to this build. I'll be lucky to fit the prototype in a shoebox by the time I'm done.
The Arduino and all the parts from Mouser showed up this week, and I spent a few hours getting nothing accomplished with it this evening. Like a complete dope, I ordered the wrong type of MOSFET, so controlling that via PWM is out. I then tried to control a digital pot and failed with that too. It seems that my digipot doesn't use the same control format as the plug-and-play SPI library. So when I plugged, it didn't play. I tried an alternate method from the Arduino forums, but no joy there either. I'll either have to find a pot which works with the library, or decipher the control interface and modify the library to work with what I have. This is going great so far.
OK, hopefully I've got the right part on order now. Apparently the key was looking for a "logic-level" MOSFET. Those guys at the Arduino forum are going to be really sick of my dumb questions before this is finished.
Candre23
would you cheakout this chip and tell me what you think about it for a pwm . Thanks
Dan
http://focus.ti.com/lit/ds/symlink/tps54620.pdf
would you cheakout this chip and tell me what you think about it for a pwm . Thanks
Dan
http://focus.ti.com/lit/ds/symlink/tps54620.pdf
For my project or something that you're working on? It wouldn't be useful for me. It could be made to work in another project, but it does require quite a few external components, and a 3.5mm QFN package is not exactly easy to work with.
Candre23
I thought it was a cool chip had a lot of features in that were good high volt low volt high current .All kinds of good stuff .Didn't think it would work for you just wanted you to look at it and tell me what you thought about it .
thanks Dan
I thought it was a cool chip had a lot of features in that were good high volt low volt high current .All kinds of good stuff .Didn't think it would work for you just wanted you to look at it and tell me what you thought about it .
thanks Dan
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