dew controller schematic ?

[Epicyclus Dave]

Hi there .

I would like to build a 2 channel controller for dew control , can anyone recommend a good schematic that i can etch or horse together on vero board , im reasonably competent at diy electronics , see here for my home made modular synthesiser electro-music.com :: View topic - MFOS Dual VCO's .

Thanks.

Dave.

[JAS]

Hi Dave,

I used the info on this site http://www.simcoeskies.com/dew/no_can_dew.html.

Jason.

[oldturk]

you could try Dewheater for TAL/Meade - homemade (the one I used) or www.dur.ac.uk/paul.clark/TelescopeHeater.pdf, which is slightly more complicated.

Good luck!

[Horwig]

another vote for "no can dew". Built it on veroboard, four channels in total, nice easy build, very good range of control.

Huw

[malc-c]

another vote for "no can dew". Built it on veroboard, four channels in total, nice easy build, very good range of control.

Huw

No issues with the spiling on the same 12v supply as the scope or other equipment ?

[Horwig]

Good point, I'm running a Maplin 12v psu, which used to run everything including my dslr, and had no issues with breakthrough on anything. Now I have a Starlight express camera, and have some patterning on it, which I've not as yet investigated. I suppose it could be the switching of the dew control, but it could be a whole host of other things.

Beauty of the simple circuit of the No-can-dew is that you can change the freq with only one capacitor if you have breakthrough. Looking again on the drawing, some snubber diodes across the load probably wouldn't go amiss.

Huw

[Epicyclus Dave]

Many thanks folks , i will give these a try next weekend .

Dave.

[Reggie]

Hi All, it's been quite a while since I posted on here, then again it's been quite a while since I've had the telescopes out Just thought I'd let you all know that I started a project some time back for an automatic dew heater, it requires a handful of components and no user intervention. It didn't make it off breadboard but I am quietly confident that it will do the job with just a few tweaks to key settings.

Quick outline of components:

1x atmega 168/328 microcontroller

1x sensiron sht11 temperature and humidity sensor

Per telescope/item that needs warming:

1x Tip120 1amp transistor

1x Dallas DS18B20 temperature sensor

Software/firmware:

1x PC app (if the user wants serial control)

1x Atmega Firmware (to actually control the tip120s/heaters)

My initial aim is to allow the scope to track down with ambient temperature whilst keeping that temperature above dew point. I derive the dew point from the sensiron sensor, using relative humidity and temperature, I then check the dallas sensor (placed somewhere appropriate on the telescope) and check to see where we're at, then act accordingly.

Total cost of unit to make should be £25-30, although I seem to be having issues sourcing the sensiron sensor at reasonable prices, I have found what appears to be a replacement that shouldn't take much in the way of coding to implement new firmware.

If anyone is interested, I'll dust off what I have so far, rebuild at least a breadboard unit and see where to go from there for an actual circuit.

I'm not the best electronics engineer nor am I a fantastic programmer so I am open to suggestions on any aspect of design and the design + software itself will be open source.

At the moment, I believe I have a java based app. that will talk to the heater over serial, at the time I was putting override functions into it but with the microcontroller I should be able to add other stuff to it too (such as a pot/button/led for manual override whilst in standalone mode).

[yesyes]

Slightly off topic, but I would be interested what that replacement for the Sensirion SHT11 or SHT15 is. I've got an SHT15 running in my Arduino based weather station but these are quite expensive.

[Reggie]

Hi Yesyes, that would be a dht22. It's not a 'drop in' replacement so if you were looking for one for your weather station, I haven't had a good look at the specs yet but for my purposes it should be good enough. adafruit do them and they're all over ebay.

[yesyes]

Thanks Reggie. Looks promising. There is already an Arduino library for that sensor.

I don't need it at the moment but was thinking of adding more humidity sensors for different places to the weather station at some point. Will keep that sensor in mind...

[Reggie]

You're welcome, What weather station do you have? Is it a retail one or something you've knocked up yourself? Judging by your website I'd say you made it yourself

[yesyes]

I did indeed build it myself... ;-)

It was my first Arduino project. It's got an IR temperature sensor measuring sky temperature and ambient temperature, a light sensor (simple LDR) and an SHT15 for another temperature, humidity and calculated dew point. It displays that on an LCD and is being polled every 5 minutes via SNMP (through Ethernet shield) and that gets logged in a database from which graphs can be generated (using Cacti for that).

But I think we've gone slightly off topic.. ;-)

[Reggie]

Well, yes and no on the off-topic, it's discussion around heat, dew and circuits, so it's all good My next question was going to be, how do you deal with dew in your setup, does your weather station deal with it or do you have a seperate heater?

I was kind of hoping for a little feedback on my heater app. idea and whether I was going in the generally correct direction or whether there was anything else I Should be mindful of.

As no one has really seen the app. (although the code is on the SGL automation yahoogroup), I'll just give a quick run down.

I measure the ambient temperature and humidity through the sht11 and derive the dew point, I then check the telescope(s) temperatures and check to see whether they're within 2c of the dew point, if they are, I turn the heater tape(s) on. then we repeat the cycle.

I have put provision for overriding the automation and allowing the user to manually turn the tapes on or off as well.

I'm thinking that I should also allow the duty cycle of the PWM pulses to be adjustable by the use? Then with a little profiling and depending on the weather they can adjust the aggressiveness of the heating to suit.

Or should this really be in it's own thread?

[yesyes]

It does sound like an interesting project and certainly makes a lot of sense.

Personally I've not had big dew problems so I have not yet build a heater even though I have a manual 2 channel PWM controller built into my Power Box. It also has an Arduino in there for focuser control. Now you got me thinking....

[Reggie]

Funny you should talk about arduino focusers too I've dusted down my unfinished focuser with a view to getting it finished. Using the SGL Automation ascom driver on yahoogroups (I was one of the original members and helped ncJunk with code/testing).

The code I wrote for the dew heater is incredibly simple, it should integrate into the focuser without too much issue, I have a version of code here that does just that. It still needs further development but nothing drastic.

I haven't been out with my scopes properly for a year or so, I'm pretty sure I'll suffer from dew, either way, I wanted a dew heater system that just does it's job, all of the kendrick etc. stuff just seems woefully expensive for what amounts to a £3 microcontroller and £20 of sensors.

[yesyes]

Yeah, materials are pretty cheap (though I would like to know where you get Arduinos for £3, I'm paying twice as much for Arduino Mini Pros ). I guess it's the time it takes them to develop and maintain the software and the company logo stickers must cost them a fortune..

[Epicyclus Dave]

I hope i don't offend any DIY electronics dew heater constructors here by saying i have been offered a Velleman PWM kit for pennies , .

Reggie & chris , that sounds very interesting with frost sensors activating the heaters, i'll get these old tapes working first before i think down that road , interesting stuff though .

Dave.

[Reggie]

No offence taken Dave, velleman for pennies is worth going for Cheap is exactly the reason I started making stuff myself. I'm even trying to etch my own boards with reasonable success so far.

I'm not getting arduinos for £3, just the atmega chip is about £3, for an automatic dew heater, once it's programmed it doesn't need a serial connection, so all it needs is 2-4 caps and a few resistors and 5v from somewhere. If you wanted to add an ftdi chip, they cost around £3 in 3s off ebay, might be able to get them cheaper in bulk. Again, they need little more than a few components to run.

[yesyes]

Ah, I see. That would be something to consider. Just buying the ATmega328 with an Arduino bootloader. It would only need one USB to serial module for many controllers with a "standardised" connector. In case they need to be re-programmed, just connect the USB module to that one controller. ;-)

I like that automated dew controller idea more and more. How do you test it? Do you have a way of simulating crossing the dew point?

[Reggie]

If you have an ftdi dongle or an arduino then you don't need to pay for the privilege of someone putting the bootloader on the chip for you, you can use avrdude and do it yourself (or save space and don't use a bootloader at all). I couldn't swear to it but I believe you should be able to use a serial adapter from your lx mod for programming once a bootloader is on the chip, unfortunately I think you need something with an ftdi chip on it to program the bootloader on in the first place as they bitbang the bootloader over spi/ISP port (in system programming). Look on a duemilanove for 4 pin header solder points marked X1-X4

As for testing, can't remember exactly off the top of my head, something along the lines of breathing at the ambient sensor to raise humidity and poking one of the scope sensors outside with the ambient sensor inside It needs proper testing in the field but the simpllicity of what it's actually doing and the code means that there's not much to go wrong with it, it really just needs trigger levels setting and monitoring of the PWM to see how aggressive the heating profile is. I had it sitting for hours testing like that too, so the system is safe (it doesn't burn scopes or tapes ).

my reckoning is that it would be around £3 for the chip, £2 each scope for the ds18b20 sensors, £1 per scope for the tip120, the only thing that has gone up is the SHT11 sensiron sensor, but one of those DHTs should be easy to replace it, so we're probably looking at around £20 for components with a cheap 5v regulator for the atmega chip (may want/need a couple of buttons and a pot for manual override).

The other thing I wanted to do was modularise things, so the atmega chip is on it's own small board and the heater control is on another, that way it should be relatively simple to knock up a design in eagle that has upto 4 heaters on it, then it's up to the user how many holes they populate, having the atmega chip seperate allows flexibility if you decide to do add some wonderous doohicky to your astronomy arsenalm or you simply want to reuse it because a better design came along.