Hi Bob....great work indeed. I was looking for inspiration and was recently reading your posts on this subject, you did last year.
I was looking at building (putting in the articles) a 4-6 channel PWM heater (I have designed & tested) and am now of the opinion that it is probably best done thru AVR (Arduino)...pretty much the same ideas you were at last year.
I sent Iceman my designs ( a week ago) for inclusion into the articles...maybe he didn't like it. I can see why now!
Mike thanks for publishing that. Hopefully it will provide a useful starting place for others wanting a dew heater controller. The design should be able to be enhanced or dumbed down (I use a more basic version to provide multi channel dimming of Led lighting in my camper trailer).
I found an additional resource today which could be useful for anyone looking a using the idea's here but is able and willing to do some alterations. A Serial LCD controller based around an Atmel chip ( http://www.arduino.cc/cgi-bin/yabb2/...num=1260399444 ). I've not worked through what's involved yet but it could be useful.
wasyoungonce, thanks for your comments. Please feel free to float any improvements you can think of, I've been learning on the job with this. I'm very happy with the outcome but suspect that there will be a range of other options.
Mike thanks for publishing that. Hopefully it will provide a useful starting place for others wanting a dew heater controller. The design should be able to be enhanced or dumbed down (I use a more basic version to provide multi channel dimming of Led lighting in my camper trailer).
I found an additional resource today which could be useful for anyone looking a using the idea's here but is able and willing to do some alterations. A Serial LCD controller based around an Atmel chip ( http://www.arduino.cc/cgi-bin/yabb2/...num=1260399444 ). I've not worked through what's involved yet but it could be useful.
wasyoungonce, thanks for your comments. Please feel free to float any improvements you can think of, I've been learning on the job with this. I'm very happy with the outcome but suspect that there will be a range of other options.
Bob
Excellent stuff Bob. The only thing I'd look at is maybe higher pwr Fets. I used IRF4095 "p" mosfets, $1.44 ea, capable, ...well in my design ...I've run at 4.8 amps per channel but recommend 3A per channel (with a simple Heatsink). I mean who would need more than 3A per channel I ask?
But that would mean a complete re-work and don't I know it...you have to settle on a design and stop changing it at some stage!
I am trying to work out the STA508A ATM...just a little confused by it. Its a H bridge driver?
But using an Arduino. Yep that's the ticket. Great work putting it on eagle PCB. I did as well.
I meant to say as well. After I pretty much finished my designs I ordered a Duemilanove kit (on it's way as we speak) as I was going to play with 6 channel PWM after re-reading your posts from last year.
wasyoungonce, I've been pondering a rework of the design to use individual fets just because the STA509A is getting hard to get.
The STA509A made a lot of sense on veroboard, not so much on a made up PCB. The STA509A is just 4 Fets with the source's already joined together which works well for the way I'm using them (and trying to do the switching between the 12V supply and the heaters looked difficult).
I won't be embarking on those mod's at the moment as I'm hoping that discussion will attract some feedback on power stage filtering, it's not been a bother to me but for those doing serious photographic work it may be an issue.
Yes I am pretty much facing a wall with power filtering. Problem is switching Hight current effects everything attached to that line....well it does on my power supply. If I had 2 ccts at 3A and another 2 and .5A...a heap of switching inrush!
I have some high current chokes from jaycar I was going to put in line & fiddle...some day!
Iceman is going to put my ccts on so you can see where I'm at, unless you want me to send you my eagle files now?
Another issue is FET on rds. I pretty much faced pdip (package power dissipation) problems when trying many FETs with .117 milli ohms rds (or so) at 3.5A. Each TO220 FET package can dissipate around 2.5W (Max) and rds on rises with I draw & pdip case increase.
So I turned to very low on rds fets....020milli ohms (IRF4905)! My ccts were designed with these low rds FETs..less pdip issues. But ATM but I am greedily eyeing some new generation automotive intelligent power switch FETs that have I fold-back... like the IR1334 or IR3316. They are designed to run from 12V and have current fold back by using a resistor and/or even monitoring with something like an AVR.
I looked up commercial dew heaters & settled on a 3A per stage max output (with a little head room). Any more is for the big boys!
Thanks Bob! I need a little project in my life, and although I build my own PWM dew controllers already I'd like to investigate this one. Looks very interesting. I'll start investigating parts today.
Minor point - the links in the article to the Arduino.cc website seem to be duds or not quite correct. I didn't check the others, but thought you might like to know.
I received some LCD displays from Satistronics today. The backlight does not appear to be working on any of them. I need to do some more investigation and I've emailed them to advise of the problem and to seek advice.
They appear to be identical to a number of display's I already had which don't have that problem (using the same dew controller and Serial LCD backpack).
I'd suggest anyone thinking of ordering them hold off until I see what their response is.
I also got some headers and pin strips from them which I use to connect the LCD, arduino and serial LCD driver to the board and they are excellent value compared to what I pay locally.
I've discovered that the backlight connections are reversed on the LCD displays. I've still not received a response to my earlier message to them, I've sent on the additional information.
I was looking to build my own dew heater controller and found a couple different designs on the internet. One had a temperature controller and wanted to combine it with another pulse modulated project using a 555 timer. Then i found your post. This is exactly what i was looking for...
Has there been any modifications to this plan since it was posted (back in 2006) or has anyone else contributed to the design? For some reason i was expecting a very high cost but after looking at the parts, i find that the unit can be build for pretty cheap and will start looking into it very seriously. Can i still contact you guys for assistance if i get lost in the process (which i'm sure will happen - never built anything electronics in 20 years)?
I'm also new to astronomy so after trying my telescope a couple times last fall, i realized that this was needed badly so started looking right away. If i can build it, i would rather do that. Plus that's more fun to say that i built it then to say i bought it...
My bad. Been following too many links . But at least i got the right link for your build, and that's the project i need...
This adruino stuff is all new to me but tha's the way to go for sure. I studied electronic engineering back in 86 and i just wish i would have kept working in that even as a hobby but life took me in another direction. I'm sure i'm gonna pop a few neurons in this project but it's worth it...
. I can see why now!
