Dew controler based LED dimmers

[Stargazer33]

Hi Dave,

Thanks for that, I will take my box to work on Wednesday and hook it up to the scope and see what I get.

Don't worry about the name. My Great Aunt used to write Brain on my birthday & Christmas cards!

[pwalsh61]

Just as a matter of interest, is China the only place such units can be obtained from? Isn't it a false economy to buy multiple units (expecting failures) than to buy a single, more expensive unit that might last a lot longer/be of higher quality?

[Epicyclus Dave]

Hi , and a happy new year all

It depends on what you need for your diy set up , in my case i needed (on a budget) objective / finder - guider / piggyback dslr / timelapse dslr on tripod , 4 channels, all to have independant variable temp control dew bands , i built my control box to have 6 channels (2 spare).

For the price these things are i understand i may have to open them up and re-flow some joints and rewire any brittle thin cables.

Most malfuctions of these units are to do with wires breaking off or bad / cold solder joints , very rarely will the components fail unless there has been a bad short somewhere.

I still think these are a great, simple , cheap DIY way to deal with dew

I hope we have less cloudy nights in 2013 to get out and actually use our diy creations

Dave.

[Chris Rowland]

I'm not convinced that the diodes connected to the pot are correct. As it's defined there's no difference between the pot being at one end or the other. But there's certainly some similar circuit with a couple of diodes and a pot that will adjust a 555 from zero to 100% mark/space ratio.

As Gina says you need a MOSFET to switch the dew heater power.

I'd put a much bigger capacitor in place of the 100nF going to pins 2 and 6, this will slow the pulse rate down so you can see it switching on and off.

Chris

[tich]

As I've only got the one dew band at the moment I've ran each channel on mine for around 12 hours or so & it's working perfectly. I did have to resolder one of the pins on one of the boards as it was looking a bit shoddy but apart from that all is well. I guess we will see how it fairs when it's outside in the cold & damp. I too am on a tight budget now so I had to go down the DIY route but it was fun building it even after a couple of frustrating moments where I just had to stop & go back to it again at a later time after some deep breaths. The extra power outlets will come in handy too & with the DIY approach you can customise it to your needs. If the components do fail then I might see about making up some DIY boards rather than buy more dimmers but we will see how it fairs should I get a chance to use it.

I just thought I'd add a few more pictures of mine, I'd like to add a couple more components at a later date like a capacitor somewhere in case of surges in power & a diode just in case it gets wired backwards to a power supply, although that is more to protect the mount than anything.

Excuse the spaghetti below, the power lead I made up is fused & is 20 meters long so ideal for star parties & here at home, the regulated power supply is an old CB radio one which seems to power everything nicely. At star parties I'll be running it from my leisure battery on my caravan with the trickle charger. The modded power lead now goes into the dew controller with the other lead going to the mount.

Measuring the voltage across one of the outlets it is reading 8.8 volts but the photo isn't great needed another pair of hands, I did find that the adjustment was very fine around the 11:00 position although when I tried a 12 volt LED strip light the adjustment was from around the 10:00 position to 3:00, the same goes for when the dew band it's plugged into it.

The extra outlets have proved handy as the Astronomiser power supply for the DSLR proved so no more flat batteries. Maybe I could use another one for a 12 volt kettle

Ok I was joking about the kettle before anyone says I'll fry something lol......

[Islander]

I'm not convinced that the diodes connected to the pot are correct. As it's defined there's no difference between the pot being at one end or the other. But there's certainly some similar circuit with a couple of diodes and a pot that will adjust a 555 from zero to 100% mark/space ratio.

As Gina says you need a MOSFET to switch the dew heater power.

I'd put a much bigger capacitor in place of the 100nF going to pins 2 and 6, this will slow the pulse rate down so you can see it switching on and off.

Chris

You aren't wrong about the diodes - one should be the other way round. They're there to separate the charge/discharge timings which is how PWM is achieved with this circuit.

[fwm891]

I bought 4 of these dimmers with 1K pots. One unit didn't work full stop and another gave me full output when from min to max positions. I found with this pot that bending the centre wiper connection down slightly it then worked properly! The pots on all mine don't look brilliant so I may change them at some stage...

[Stargazer33]

You can't drive a dew band directly off a 555 - you want a power MOSFET in between. The 555 output goes to the gate, the source goes to ground and you connect the dew band between the drain and the +12v supply. Power MOSFETs are readily availably from ebay. eg. http://www.ebay.co.u...=item4ab74e27ed You can get 5 for £4. They are switching devices and don't need a heat sink.

Sorry Gina I missed your reply to my post about the 555 circuit. Thanks for the info!

It looks like my Chinese dimmer is actually working - I hooked up a 12v bulb and it brightened with the pot rotation. It still only works from about 9 O'clock to 1 O'clock (0.00A to 0.30A) but at least I get a reasonable amount of rotation on the pot. I had to put 2k5 ohms of resistors on one of the pot legs to bring the usable arc to the 9 O'clock position but at least it is working.

[Stargazer33]

I bought 4 of these dimmers with 1K pots. One unit didn't work full stop and another gave me full output when from min to max positions. I found with this pot that bending the centre wiper connection down slightly it then worked properly! The pots on all mine don't look brilliant so I may change them at some stage...

Sounds like the wiper wasn't making contact with the track so you weren't getting the take off through the centre wire - you were just getting the full sweep between the outside wires. At least you managed to save one of them!

I seem to have found a different supplier to everyone else as my pots are of 5K value.

There seem to be an awful lot of these dimmer controllers on Ebay now. All slightly different in design or with different coloured knobs, different circuit board designs and colours. Presumably they are all clones of the original, more expensive, units!

[Gina]

My pots are 5K too.

[badgers]

I'm planning to build one of these dew controller systems and extend it into a mount hub.

I want it to accept input from my Maplin 12V 10Amp regulated PSU and distribute it to 3 or 4 DC sockets and the dew control system.

The designs on here look perfect and I've ordered the LED dimmers already.

The cleanest design I can think of is a single 2.1mm DC input socket that connects to the PSU and then via a terminal block, distributes power to 2.1mm DC output sockets, the LED dimmers and a TS focus controller internally.

My problem is that my unit could potentially be drawing over 5 Amps and I can't find any 2-2.5mm DC input sockets rated above 5amps.

Does anyone have a suggestion about how to accept power from the 10Amp psu safely before distributing it ?

I guess I could hard-wire the PSU lead into the unit, but that won't be the neatest option.

I'm an electronics moron, so please be gentle with me

Anton

[badgers]

Edit: I did finally find a 10 Amp 2.5mm DC jack

http://www.cliffuk.co.uk/products/dcconnectors/FC681495.pdf

Hopefully, I'll manage something as neat as the ones I've seen here.

[badgers]

Mine is complete after a mammoth 3 day building session.... Never done any real electronics work before, can't say I enjoyed soldering all those switches and LEDs.

12V DC in,  with 7A master fuse

4x DC out each with 2A fuse and switch.

2x phono sockets out with PWM controller dials and LED indicators.

Will attach my focus motor and USB hub on top and hopefully have all my stuff in one place and eliminate some cable clutter.

Thanks for all the help from this thread, I've got something not far off a mount hub pro and total cost all-in was only around 35-40 quid.