A proportional LED colour head for Durst 138/139

Please note, this is a copy of a post I wrote yesterday on the APUG "The smoking solder iron - DIY" group.
As it might be of some interest for LF DIYers, I would like to share this project on the LFP DIY forum too.

At last, I found a moment to finish this project of a LED head for a 5x7 Durst 138/139 enlarger, I have started 6 months ago.
The design is very similar to my first home made LED head I presented on the APUG "The smoking solder iron - DIY" group except this one is far more powerful (the first prototypes were for a 4x5 Omega enlarger).
I was very close to finish the omega LED head project , when I found a Durst 138/139 on Trademe (our local ebay here in NZ).
Those 5x7 enlargers are so rare here in those latitudes, I could not resit to break my piggy bank and replace the omega with this beast

Anyway, here are the characteristics of this new head:
* 3x independent colour channels (R,G, B)
* Each channel is current controlled. The amount of light can be adjusted in real-time thanks to a PC software and a remote control
* The transfer function of each channel has been linearized
* In its current configuration, the maximum power consumption is ~85W (equivalent to a ~500W light bulb at least). I could extend it to the limit of my driver (120W). This would require me to invest in a new and big power supply but as my darkroom is quite full, I prefer to avoid it for the moment. The head might be run at 150W with a more powerful driver (~ 900W light bulb) but this, I'm sure, won't be necessary.
* Cold design (the LEDs are mounted on a big heat sink)

The red channel has a maximum power consumption of 11Watt. The red light is only used as a safe light for B&W so there was no point to increase its power. It is composed of 4x high efficiency LZ1-00R200 LEDs (Uf=2.8V, If=1A, lambda=660nm, manufacturer: Led engine)

The green channel is composed of 30x 941-XPEGRNL100D01 high efficiency LEDs (Uf=3.55V If=0.5A, 133 lumen, lambda= 520nm, manufacturer: Cree). At its full power, the green channel consumes 35W. It might be extended to 52W if necessary but actually the current is limited to 350mA per led to fit my power supply). The amount of light produce goes up to 3200 lm!

The UV/blue channel is made of 32x unbranded UV 395nm LEDs bought on ebay. They are rated 3W but I am using them at ~1W for the moment. I suspect from the shape of the die they are EP-U4545V produced by EPILEDS but who knows. Anyway here are the EPILED UV LEDs characteristics (Uf=3.8V, If=.7A, 40lm). The actual maximum power consumption of the blue/UV channel is ~37W but I did a try at 57W and it works like a charm!

Some pictures of the head:

On the right, the light source of the Durst139, on the left my home made light source
On the bottom left, the remote control which is connected to the driver.
The LED head is on and we can easily see the network of green and UV/blue led.
http://farm4.staticflickr.com/3744/1...9bec3c0ce9.jpg
My DIY B&W proportional LED head for my Durst 139/138 enlarger by stormpetrel_geek_mode, on Flickr

At full power!
It is VERY bright indeed. The heat think and the LEDs remains at room temperature. This is very impressive. I expected more heat generated by the LED.
It might be another story once fitted in the enlarger head box, but this enlarger came with an air duct and a fan to cool down the krypton head light of the durst 139, so it will be very easy to evacuate the heat if necessary.

http://farm6.staticflickr.com/5498/1...6eeeab5f94.jpg
My DIY B&W proportional LED head for my Durst 139/138 enlarger by stormpetrel_geek_mode, on Flickr

The red channel:
http://farm8.staticflickr.com/7326/1...179bf759cf.jpg
My DIY B&W proportional LED head for my Durst 139/138 enlarger by stormpetrel_geek_mode, on Flickr

The next step will be to try the head with 5x7 enlargement. However I will have to make an adapter for a Nikkor 210mm lens first as it is the only 5x7 enlarging lens I own.
Unfortunately it is quite a big lens designed for the Devear enlargers, and it does not fit on the Durst.
Maybe this weekend.

The driver is a home brewed design. The driver board contains a PIC microcontroler and 5x voltage/current converters which can deliver 2A max each.
The driver board is controlled through USB by a home brewed PC-software.
To be darkroom compatible, I had to remove all the computer LEDs. I have also replaced the monitor back-lighting with white LEDs and red LEDs.
Thanks to a push-button, I can skip from one background light source to the other (white -> off -> red -> off -> white). There is a video showing the full system in the APUG link below but the enlarger part has been rewritten since to be compatible with the new LED head. It is in french but the comments are not so important.

For the full story about the LED wavelength choices, drivers, please read the post I wrote on the APUG "The smoking solder iron - DIY" group. I might post the full story here too if you wish.



Cheers, Dominique

Nice going! The real problem with color printing will be trying to optimize the three light sources to the necessary spectral sensitivity of color paper or film, which
will likely involve "trimmer" filters to cut off unwanted spectral output in each, as the respective spectrograms indicate. And this in turn is related to operating temperature, if realistic dichroic filters are involved. So there's quite a bit of complication standing between "it works" and "it works well". For optimum results you
need relatively narrow-band RGB performance, not just a perceived color. But give it a whirl color printing and tell us how you like the result!

You are perfectly right Drew, but this head will be used for B&W printing only. As mentioned in the text, the red channel is only used as a safe light for B&W printing.
It is technically speaking a RGB head, but not a proper head for colour printing.
The blue and green LED wavelengths have been selected to optimize printing on MG paper.
The thread title might be a bit confusing, I will change it if possible.

Cheers, Dominique

Unfortunately, I can not find a way to change the thread title.

Note for the new readers: this is a RGB LED head for B&W printing only.

I already knew that.... but any experimental device of this kind is just going to help pave the way to a real LED colorhead, once the correct bulbs are available.

Great effort ... worthwhile endeavor ...

Very interesting and great work. I think it wise to post all of it here as well as APUG simply so we don't lose valuable research like this.

Thanks for your efforts!

Fine project Dominique... Inspiring work.
Bill

Thank you all for your kind comments!

I will post here all the important information relevant to this DIY head in this thread too.

Cheers, Dominique