I was researching DIY dew controllers when I came across this thread. I have a few questions I hope someone here can answer. I have two Kendrick heaters - one for the eyepiece and the other for my quickfinder. I may add a resister to heat the secondary mirror. I want to experiment with some baffling first to see if that is necessary. So I need a controller that can potentially handle the three dew prevention devices.
besides the fact that it keeps the dew off of the optics
whats the point?
its just a heater right?
(yes im a noob, dont kill me)
Correct.
The key is to be able to adjust the amount of heat, so you can use as little as possible to prevent dew forming. It takes a lot more energy to get rid of due once it forms, than it does to prevent it. Use too much heat and you create thermal air flows that distort your vision/image.
The RS controller will easily do the load you are talking about. I run four heater straps (2x4" and 2x2" diameter) no problems. You need to choose the type of connectors carefully as the -ve terminal goes to 12V relative to ground when you reduce the output to minimum (I think this is discussed in this thread).
Is it OK to fit a LED into the out put circuit to aid in adjusting the PW? The LED dims and brightens when the pot is adjusted and I've also added a on-off switch. Thanks for this well written article AL...
Thanks for the advice. My heatstraps have RCA connectors. One has exposed metal so I will cover that with heatshrink. I'll probably go with the RS components controller since it costs little more and saves time.
I've got moving again on an Ardunio controlled PWM heater. I had the whole thing on hold for a while dithering over heater straps, I did some work on making my own and decided that I was going to spend a fair bit anyway and was no confident that I'd get a good result. I ended up getting a number of Dew-Not heater straps which so far seem great.
The controller is more complex than many find necessary but component count is low (and the ugly bit's are in the power stage which I'd need anyway) and I'm using it as a learning exercise to get across some of the technologies.
I've got the important parts of the dew heater controller working
- 4 independent PWM channels each with a dedicated temperature sensor.
- Dew point calculation based on ambient temp and relative humidity (I expect that the calculations will be suitable for the conditions I observe in)
I'm planning some extra work soon. A red on black serial LCD screen, a current shunt/sensor and an extra Ardunio are on order. I'm planning to
- Add voltage monitoring (2 resistors, some code and a hookup to an analog pin on the ardunio) to try and avoid running batteries right down.
- Add current monitoring, combined with the voltage monitoring and controlled cycling of the power channels and the controller should be able to work out what's hooked up to it and adjust the behaviour of the different channels to suit. I'm guessing that a 1.25" eyepiece will benefit from different heating patterns vs a large corrector plate or the front lens of a finder scope.
- Add the LCD so that I can see on the controller what's happening, I can monitor via a laptop currently but that's not always ideal or practical
- Tidy up some wiring
- Swap the ardunio over to a cheaper and slightly more basic model (and use the current one for developing something else)
- Fix some indicator led's which are not working
- Review the code to see if there are tidy up's I can do
I've now fitted the LCD screen and got the main values displaying on it. 16*2 characters is not a lot of space but I can fit the main values on at the same time (although I won't have space for supply voltage).
Next up will be fitting the current and supply voltage measuring components and making up a couple more temperature sensor leads.
Here's one I'm knocking up for AlexN. The controller board is from Oatley Electronics, $25 delivered. 2 controlled outputs on top and 3 12v raw outputs on the left. Cheap and functional
Here's one I'm knocking up for AlexN. The controller board is from Oatley Electronics, $25 delivered. 2 controlled outputs on top and 3 12v raw outputs on the left. Cheap and functional
Looks Like a nice kit. On a small side track, has anybody ever seen a gadget (kit or built) that is a USB-controllable PWM 12V supply? My thought is for a generic PC-controllable variable supply that can be used for focusers, dew heaters, lights, whatever.
I am aware JMI etc sell such an item for focusers, just wondered if there was a kit or similar project floating around so that a general purpose USB 'control box' could be built for the obs.
The world of RC hobby electronics has many such potential items, as does computer overclockers accessories.
If this is more suited to it's own thread, please feel free to let me know.
In any case interference to radio services is due to the speed of the switching transients, which can be smoothed out in circuitry. Whack a capacitor on each output.
If I were designing one I would prefer a faster cycle time in the hundreds of hertz to avoid transients on the dc supply affecting other electronics such as the argonavis.
Geoff, possibly because it may show in your USB data feed coming
from your imaging device?
The last thing you want in your dome is something emitting RFI.
Modified webcams can pick up RFI really well because some of the
circuitry added to the CCD pins and timing chip act like wonderful
antennas.
The problem is made worse when you extend the CCD legs to
install it into it's own cold chamber or Peltier heatsink.
Trust me...been there.
Here's one I'm knocking up for AlexN. The controller board is from Oatley Electronics, $25 delivered. 2 controlled outputs on top and 3 12v raw outputs on the left. Cheap and functional
Sent for one of these about a week ago just waiting on delivery. Have you used one? Are they good? I have made a Dew Heater from some resistance wire (from JayCar) and some velcro strip and was going to use teh controller to control the heater.
Yep, I put a pair of them into my controller box and got the straps from hong kong along with some other stuff. However, last night I dewed up as I forgot to turn them on I have an LED across the output with a 1.2K resistor and it is a good indicator of how much juice your pushing out.
The last thing you want in your dome is something emitting RFI.
Modified webcams can pick up RFI really well because some of the
circuitry added to the CCD pins and timing chip act like wonderful
antennas.
The problem is made worse when you extend the CCD legs to
install it into it's own cold chamber or Peltier heatsink.
Trust me...been there.
Steve thanks for the explanation. As I dont use cameras I didnt think of that.
I have worked in the radio comms business for many years and can tell you that rfi from a switching dew heater should be very easy to tame.
Its not so much the switching cycle speed, but radiated harmonics from the switching transient. This can easily be remedied.
I too have been busy on other projects (those pesky home improvement things) but aquired an Arduino and have been playing it. As you had stated previously, the Log function does allow me to calculate the dew point.
Curious about which temperature sensors you are using - the Dallas 1 wires or discrete? Are you measuring the relative humidity and again which sensor?
I had decided to use an LCD only for prove-in and not integrate it into the final project. I will integrate a ISP/communication port so I can monitor the project with the laptop. The final board will have the ATmega328 (with or without bootloader) implemented directly. May even be the possibility of a Astronomy Dew Heater Shield in the future!
I have an LED across the output with a 1.2K resistor and it is a good indicator of how much juice your pushing out.
