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Dew controler based LED dimmers


astrovirus

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If you've still got one wire attached then reattach the other two in sequence so that none of them cross over the others. That will give you the correct connections. Sketch the way it's connected before you start in case you break the other one by accident and lose orientation ;)

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Don't panic... You only need to solder two wires from the connector to the potentiometer (the thing used to adjust the brightness). So long as one is connected to the middle pin on the potentiometer, and the other connected to one of the other pins on the potentiometer it should work.

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The potentiometer is just a variable resistor which will give a 0 - 100% resistance based on its value. So for arguments sake, if it's a 10K linear potentiometer then the resistance will increase from 0 ohms to 10,000 ohms proportionally along its track as you turn the shaft which has the wiper attached.

replacing-your-innards-pot-diagram.gif

So long as one wire is attached to the center (wiper) pin, the connection of the other wire to one of the other pins simply dictates the direction of the knob, thus whether the leds brighten or dim as the dial is advanced. Hope that helps

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Well what can I say thanks very much for all your help especially for the diagram ,now I understand the wiring of a pot.I managed to extend the wires to suit my box,and can`t wait for my other three dimmers to arrive.Will post a pic when its finished.

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You need to have both ends of the track of the potentiometer connected - one end provides a charge path for the timing capacitor, one a discharge path - that's how the pulse width is varied. Connecting one end of the wiper won't work.

Don't panic though, the two outer wires on the PCB go to each track end, and the middle one goes to the wiper. If you get the outer ones the wrong way round then the potentiometer will work backwards - just reverse the track end connections as previously described. :)

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Thanks for the further info,i have just checked the wiring from the pot to the pcb connection,and yes i have the middle terminal on the pot connected to the middle terminal on the pcb,so hopefully when i power up the worst thing that can happen is reverse operation on the pot .Everyone is of great help on this forum and I thank you all!!

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A wee diagram......

Hi followed this topic with interest.....just getting the the bits together for my controller, 680R for max output, is it needed on every LED controller if so is it a metal film resistor? what wattage?

Thanks

post-16688-0-64045200-1348571107_thumb.j

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  • 5 weeks later...

I've just finished building my 4 channel controller & all seems to be ok although the box I used is a tad on the large side. But then I haven't got the most nimblest of fingers so probably not a bad thing. As I've modded the power supply to my NEQ6 I've incorporated the same to the controller so I can plug the power supply straight to the controller then the fly lead plugs to the mount. I ended up keeping things simple so I brought a power supply for my Canon 1000D from astronomiser, so if I change the camera in the future I can just buy a different power supply for it if needed.

I've fitted 3 marine sockets as it's handy having more outlets maybe one could be used for the electric focuser although I haven't decided yet. I still need to get a couple more dew-bands especially one for the secondary but the one I need isn't easy to find but I'm sure one will turn up.

IMG_8630.jpg?t=1356623485

IMG_8631.jpg?t=1356623498

IMG_8632.jpg?t=1356623517

Now I've just got to find somewhere to mount it to.... :rolleyes:

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Please help! My pot has turned into an 'On/Off' switch!

I have just moved my dew band controller into my new mains power supply box and now the pot shows no volts until about the 11 O'clock position and then the next couple of millimeters of rotation the output goes up to 12.5v! The output then drops almost immediately to 12.3v and stays at that level right round to the end of the track - 5 O'clock position.

I have tested the pot itself, connecting my meter across the lugs on the bottom of the pot and I get a normal gradual increase in resistance from 0 to about 5.26k Ohms. So I know I haven't damaged the pot itself. The ribbon cable wires from the PCB to the pot kept breaking off so I replaced them with single wires, but I believe I have wired them up as they were.

I have to be honest and admit that I didn't take any anti-static precautions!

So have I fried my board or am I doing something really silly? I have put the fuse for the circuit on the output power side, i.e. after the controller PCB, but that shouldn't make a difference; right?

post-21511-0-15192600-1356799682_thumb.j

Any help would be gratefully received.

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Putting the fuse on the output side means that I'll only protect against a short in the dew heater - it won't protect against a short on the controller board - which putting it on the input side would - but it shouldn't make a difference to the output voltage :).

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Putting the fuse on the output side means that I'll only protect against a short in the dew heater - it won't protect against a short on the controller board - which putting it on the input side would ...

Ahh, good point! Looks like I have a bit of re-wiring to do. :wink:

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I've now rewired my power/dew controller box with the dew controller PCB now wired after the fuse to protect that also.

I have also resoldered a couple of components that looked as if they needed it and changed the wires round from the pot to the PCB. As stated earlier in this post all that did was reverse the direction of the pot. I also tried putting various resistor values on the different wires from the pot and I managed to move the 'on' position to about the 9 O'clock position but I couldn't expand the distance of travel for full output.

Working on the dimmer again I noticed that it went from 0.06v to its initial 'on' position at about the 11 O'clock position as previously stated but the increase to 12.5v was probably over 1mm of travel. The output then dropped very gradually to 12.26v over the rest of the pots travel - i.e. to the 5 O'clock position.

I now believe that the PCB is U/S, which is probably my fault for not taking ESD precautions, unless someone can suggest something that I can try. I have ordered two more dimmers to fill the other two spaces on my new box, so it looks like I need to order one more.

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I must admit that I was thinking about making up my own controller possibly using a 555 as in this circuit.

LED-Dimmer.gif

I understand that this will adjust from 5% to 95% power, but if you change the 1N4148 diodes for germanium diodes then you can go from 1% to 99% which should be enough.

The dew band socket will obviously be where the LED is in the above circuit.

I have just ordered two new Chinese LED dimmers so I may as well see how long they last. As I have provided for three dew band controllers I may just see if I can build one of these circuits and see how it holds up against the Chinese ones!

I checked the resistors and diode on my faulty dimmer PCB and they were all okay so I guess its either the IC or the MosFET that has gone U/S.

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These units don't seem very reliable - I've had two die on me and I've given up on them now. I'm producing my own with Arduino control.

I'm a bit gutted now after reading that as I've just built mine. I've left it on today for around 8 hours & counting so far & it's still working now with a dew band in one of the channels. It seems to be ok for now so I will have to see how it performs when I'm outside. I still need a couple more dewbands & I'll test the rest of the channels over the course ot the week for a few hours each & see if they work or not as the case may be. I didn't alter the circuits I just took everything apart & fitted it in the box. I did find when I checked the voltage on the outputs the voltage only ever seemed to change around the 11:00 position although with LED's & the dewband is plugged in the adjustment seems to go from the 10:00 position to 3:00 which seems to be much better.

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I must admit that I was thinking about making up my own controller possibly using a 555 as in this circuit.

LED-Dimmer.gif

I understand that this will adjust from 5% to 95% power, but if you change the 1N4148 diodes for germanium diodes then you can go from 1% to 99% which should be enough.

The dew band socket will obviously be where the LED is in the above circuit.

I have just ordered two new Chinese LED dimmers so I may as well see how long they last. As I have provided for three dew band controllers I may just see if I can build one of these circuits and see how it holds up against the Chinese ones!

I checked the resistors and diode on my faulty dimmer PCB and they were all okay so I guess its either the IC or the MosFET that has gone U/S.

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.
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When I bought my Chinese LED dimmers, I doubled up on the quantity I needed (bought 8) knowing by experience that these things fail frequently.

Over the years I have bought all sorts of gear for photography ie, triggers for flash units etc from China, and at least half of them have failed.

Fortunately, this batch is still working but it's early days yet and they haven't had much use. I think the more we mess with them the quicker they fail.

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Hi Brian , i noticed you have a 5K pot on your dimmer circuit , on my ones i ordered in they all had 1K pots , my resistor mod on page 5 of this thread relates to a dimmer box with a 1K pot .

The control pot varies the circuit pulse width (PWM) , if it is possible try to test the unit on an oscilloscope to see the pulse narrow at min setting and widen out at max setting , measuring voltage at the pot doesn't really work as it varies a 12v narrow pulse adjustable to a 12v fat pulse , the circuit is pre-set as to the frequency or speed of the pulses. you may just have a bad one , i ordered 8 in total ,4 each from 2 different suppliers incase of a bad batch.

If you can i'd recommend setting up a dew band with a temp probe at the work bench and write down what temps your getting at the position of the pot , a bit more time consuming but it helped me understand what my ones were doing.

Good luck .

& happy new year tonite :)

Dave.

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