How-To: Building a Pulse Width Modulated Dew Heater Controller - Page 2

mldee (Mike) · #21 04-04-2009, 07:33 PM

Peter, you're a lifesaver.
This is just the answer! I can't be bothered with kits anymore, or rather kit components can't be bothered with my eyesight, and this looks like the answer. Price is right too.

I can see uses for not only dew heaters, but motor controllers for focussers, etc.....

peter_4059 (Peter) · #22 04-04-2009, 10:54 PM

No problem Mike. Here's a pic of mine all dressed up....

erick (Eric) · #23 05-04-2009, 09:55 AM

Quote:

Originally Posted by troypiggo

I went into Jaycar last weekend, and while the guy who served me was (trying to be) most helpful, he threw so many different alternatives at me that it confused me more than helped. Went in asking for something specific and he went round in circles trying to get me to use everything except what I asked for! I'm now back to sticking with the tutorial and will just ask for what's on the list, no variations from what I want. Now I am just doing the research on what I want

I'm pretty sure it's the 5k trimpot. That much I can sort out on the spot by opening up the kit in store. It's the log/linear thing that I'm not sure about.

Troy, you want a 5k linear pot. I need one myself - just built up the Jaycar kit last night. It's been on the shelf for a couple of years - now I need it to control an individual heater. After the build (I havn't made up a circuit in years), it checked out fine.

troypiggo (Troy) · #24 05-04-2009, 10:30 AM

Thanks for the confirmation. That's what I suspected but always better if someone with more experience agrees with me...

erick (Eric) · #25 05-04-2009, 12:13 PM

I recall log pots were mostly for volume control in audio systems, but I'm sure there are many other uses as well.

mldee (Mike) · #26 06-04-2009, 03:54 PM

Thanks Peter, looks good. Now if you could just find the RS number for a USB-controlled version.....

Glenhuon (Bill) · #27 06-04-2009, 11:45 PM

I used a 5k linear on mine. Gives a good wide adjustment range.

Bill

MrB (Simon) · #28 07-04-2009, 12:20 AM

Yes the 5k linear pot is the one you want. It is marked 'B5k'
Cat# RP3508 for the 24mm or RP7508 for the 16mm one.
Helped a customer with this very thing the other day... though not for a dew heater.
No it wasn't me that served you Troy

troypiggo (Troy) · #29 07-04-2009, 05:33 AM

Sweet. Thanks again guys.

hikerbob (Bob) · #30 07-04-2009, 08:02 PM

Has anyone played with one of the Arduino variants as the basis for a Dew heater controller. http://www.oceancontrols.com.au/cont...o%20Pro%20Mini for some info on them.

I've not tried one yet but with multiple analog inputs and digital input/output they seem like they could be combined with multiple temperature sensors and a power stage and possibly a humidity sensor to create a fairly potent controller.

The Arduino Pro Mini http://arduino.cc/en/uploads/Main/ArduinoProMini.jpghas the following specs
Summary

Microcontroller - ATmega168
Operating Voltage - 3.3V or 5V (depending on model)
Input Voltage - 3.35 -12 V (3.3V model) or 5 - 12 V (5V model)
Digital I/O Pins - 14 (of which 6 provide PWM output)
Analog Input Pins - 6
DC Current per I/O Pin - 40 mA
Flash Memory - 16 KB (of which 2 KB used by bootloader)
SRAM - 1 KB
EEPROM - 512 bytes
Clock Speed - 8 MHz (3.3V model) or 16 MHz (5V model)

Also a digital temperature/humidity sensor for $42US http://www.sparkfun.com/commerce/ima...-01-L_i_ma.jpg
http://www.sparkfun.com/commerce/pro...oducts_id=8257

I'm interested to find out if anyone else has played with this technology in case I'm missing something fundamental here.

Bob

peter_4059 (Peter) · #31 07-04-2009, 08:25 PM

Looks interesting Bob but will it handle the load alone or is something else needed (not sure what a power stage is?). The power requirement for an ED80 is about 6 Watts. Also looks like it needs some programming?

Peter

hikerbob (Bob) · #32 07-04-2009, 09:17 PM

The output power is very low so I assume that you would then need to include something to turn the low power pulse width modulation (40mA I think) into something suitable for driving heaters. I've not done much looking for a circuit for that yet but for a start something like this might be useful http://www.sparkfun.com/commerce/pro...oducts_id=8907. There are probably better options around and I don't think that one would use the Arduino's onboard PWM.

Definately some coding involved but if it's suitable that's something some of us may be able to brainstorm and share.

I've found another local supplier with a different range of boards and seemingly lower prices http://www.littlebirdelectronics.com...tions/arduino/. One is a bare bones board for $22.46 but I'm more tempted by the $44.99 version with the USb port etc. They also have the temperature/humidity sensor I mentioned earlier for $65. I'm assuming that you would use one of them to get the ambient temp and humidity and a straight temperature sensor to get the temperature near each of the heater strips.

I've not yet had much of a look around for a straight temperature sensor but this one from SparkFun looks promising (looks like it's out of stock at the moment though) http://www.sparkfun.com/commerce/pro...roducts_id=245.
There is sample code for reading the sensor from an Ardunio at http://www.arduino.cc/playground/Learning/OneWire

I also just found this little device http://www.sparkfun.com/commerce/pro...oducts_id=8855 which on first impressions might do a similar job but with a small LCD screen built in. I've not seen it before. I've not quite worked out if a seperate programmer device is needed for this.

Bob

Nico (John) · #33 07-04-2009, 09:25 PM

Try this one, its cheap to build, and all parts probally set you back no more than $15. The heating element can be purchased from Jaycar, part no. WW4040. Also required is a length of heat resistant tubing to feed the element into, part no. WS5504.

The heating element is a special type of wire known as Nichrome wire whereby its resistance measured from one end increases as length increases. Its the same kind of stuff used in toasters, although you would definitely not want your element to glow red hot.

I feed the wire through the tubing then using some insulating type of flexible foam/rubber mat (roughly 25mm wide x dia of OTA) taped the tubing (with the element contained within) to the rubber/foam with a long strip of gaffa tape, then just folded the edges round the back to make it neat.

You'll need to solder the ends of the nichrome wire in order to make a good connection with the output of the PWM circuit. I tried a few ways (nichrome wire is difficult to solder) and found that by lightly removing the surface of the wire I was able to solder it to a couple of female spade terminals (remove the plastic insulation before soldering, and apply stacks of heat + solder) once cooled down just slide the insulation back on, or just use tape!

Stuff the circuit (made mine on a piece of viro board, also at Jaycar or dicksmith etc..) into some kind of plastic jiffy box and mount the led through the lid (so you can see the PWM in action), connect the load (element) and you're away.

http://www.backyard-astro.com/equipm...dewheater.html

montewilson (Monte) · #34 08-04-2009, 07:07 AM

I have two nichrome elements around my FSQ. It has never failed me and last year I upgraded the set-up so it has temp control for the tube and element.

I set the temp for the night and it stays at that temp! I focus it at the start of the night and it never varies - cool eh?

It has two digital temp controllers from a refrigeration unit and sensors on the metal of the tube. The whole tube is insulated. It looks ugly but is very effective.

Omaroo (Chris Malikoff) · #35 08-04-2009, 07:50 AM

Quote:

Originally Posted by montewilson

The whole tube is insulated. It looks ugly but is very effective.

It doesn't look "ugly" Monte - it looks positively industrial.

Doing the same to my 102 I think.

montewilson (Monte) · #36 09-04-2009, 07:25 AM

The wiring is a bit of a mess but that's because I jerry-rigged it to use the 20Da someone lent me. You can see the controllers inside the box top right.

montewilson (Monte) · #37 09-04-2009, 10:12 AM

Call me if you want any advice based on my experience of the set-up.

Quote:

Originally Posted by Omaroo

It doesn't look "ugly" Monte - it looks positively industrial.

Doing the same to my 102 I think.

Omaroo (Chris Malikoff) · #38 09-04-2009, 10:29 AM

Yeah, cheers Monte

I already have my home-made 4-channel PWM controller - all I have to do is build a feedback system for it.

Where's the foil look gone on yours? Both tubes were wrapped is Sisalation or something similar at IISAC, making them look like they were off a satellite. Very cool...

I take it that these images are old?

montewilson (Monte) · #39 09-04-2009, 10:39 AM

Too much Shiraz mate! It has looked like this for a while including at IIS.

The big difference is the lack of the STL

This was taken last week.

Omaroo (Chris Malikoff) · #40 09-04-2009, 11:09 AM

More likely not enough! LOL

Ok - my mistake. I can see your tubes are wrapped - but in a white material, not aluminium. I remember thinking that I had some foam rubber-backed aluminium that I was going to use on mine. Not yours. I became horribly confused and in a moment of indecision I posted what i did. Arrghhh!!

Maybe you're right.... to much shiraz...