MicrobeHunter.com Microscopy Forum

It made a huge weight difference. Mostly the transformer.

No turning back now. It gave me a chance to clean-up the unit. It wasn't in terrible shape, but it was gunked up so might as well.

Definitely will do...
- Use a laptop 19V external power supply (Considered USB-C, but I had the flush mounts for the barrel connectors already)
- White LED 3-5W (dimmable)

Most likely will do...
- The plan is to keep the dimmer function on the dial.
- Add USB hub (to allow for cable management for camera..
- Add USB PD 3.0 output ... charge my phone?

Maybe....
- Ethernet port (Via RPi) <- maybe also for camera control.
- Temperature monitor for lamp unit (no purpose.. but I have some thermistors and if I throw an Rpi on it, might as well)

I'm still trying to decide on which LED I want to use.

Nothing too drastic or major. I like the microscope.

I was about to implement a PWM dimming…

Then it occurred to me, would it make a difference?

With analog dimming I lose efficiency but I avoid flicker which may matter for digital images/video.

The other downside with analog dimming is the light output changes in spectrum.

What are the experiences here?

If I do analog dimming, I don’t have to buy parts which is another good reason for me since I have things lying around.

You want a PWM with a refresh rate of 25kHz or better to avoid banding on digital cameras.

I'd also recommend using an LED without a lens, to avoid introduction of CA. Luminous panel type LEDs seem to work better for me in that regard, anyway. If you do that, 5W may not be enough light, depending on whether you are using phase contrast, DIC, etc. At 10W and certainly above you need to be careful about your power supply, and select a correct constant current version.

Watching this topic....

Curious to see how you work that dimmer into your LED and power supply.

I've got a similar setup and I too would like to use the onboard switches and dimmer. As it is, my lighting setup is arc-welder bright; thankfully the DIC eats up most of that and, in a pinch, a couple of polarizers over the stage light does a fair job of dimming things.

ldflan wrote: ↑

Mon Feb 13, 2023 3:28 pm

You want a PWM with a refresh rate of 25kHz or better to avoid banding on digital cameras.

Idflan - does that mean you would recommend PWM? Or just do 25kHz if I go that route. That’s good info and appreciate it.

Also, I planning to under-drive a 10W LED. So I can adjust accordingly. I have 3200K and 15000K white LEDs in a bin for a previously project.

I do have a light meter and I can measure the spectrum. I’ve read the best is to shoot for 5000K but others imply 6500K might be better. One source said 3000K… I know a lot of that depends on the LED too…

Thx again!

Sure Squintsalot wrote: ↑

Mon Feb 13, 2023 6:31 pm

Watching this topic....

Curious to see how you work that dimmer into your LED and power supply.

Will do. I chose 19V because it’s everywhere. I thought about a USB-c setup but the flush mount and regulator cost $20.
An annoying expense when I already had the power supplies from old laptops lying around.

For power, I’m using a DC-DC step down that’s like a $1 rated for 0-30V and 5A. Not the most reliable at the edge of their specs but again, driving one LED at 3-5W.

For the dimmer dial, it’s a straight substitution of a common potentiometer. In fact, you can probably keep the one currently being used with no much effort.

Another way is to have the original pot drive the analog input on an arduino or Pi and send the PWM signal that way.

But then that adds cost and unnecessary complications. I decided I wanted to keep it simple else I’ll never get around finishing the project… not to mention more points of failure.

My USB output is easy. I can splice 19V to a USB board. I don’t remember how much I paid for them but I have a ton lying around for powering cameras on my 3D printers by taking the 24V supply. So it’s “free-ish” and I might as well use them.

The simplest approach is probably a buckblock, the main downside being they max out at 2100ma so you can't drive e.g. a Cree XP-L at full power, but they still run very bright. Otherwise implementation is incredibly easy.

hypancistrus wrote: ↑

Mon Feb 13, 2023 7:22 pm

Idflan - does that mean you would recommend PWM? Or just do 25kHz if I go that route. That’s good info and appreciate it.

Also, I planning to under-drive a 10W LED. So I can adjust accordingly. I have 3200K and 15000K white LEDs in a bin for a previously project.

I do have a light meter and I can measure the spectrum. I’ve read the best is to shoot for 5000K but others imply 6500K might be better. One source said 3000K… I know a lot of that depends on the LED too…

I would recommend going the PWM route for consistency of color output and LED longevity. Underdriving it may create some dimming issues.
Color temperature is a matter of personal preference, and trying to avoid CA. Many people, myself included, find the warm temperature of halogen lighting to be easy on the eyes and look good. Halogent bulbs are about 3000K. I usually shoot for 3000K to 4000K for an LED...

Scarodactyl wrote: ↑

Mon Feb 13, 2023 8:43 pm

The simplest approach is probably a buckblock, the main downside being they max out at 2100ma so you can't drive e.g. a Cree XP-L at full power, but they still run very bright. Otherwise implementation is incredibly easy.

Agreed. I use a couple versions of the same made by Keystone that are programmable (but the harness to program them is stupid expensive). You can dim the 0-10 circuit with a pulse width modulator.

hypancistrus wrote: ↑

Mon Feb 13, 2023 7:22 pm

I do have a light meter and I can measure the spectrum. I’ve read the best is to shoot for 5000K but others imply 6500K might be better. One source said 3000K… I know a lot of that depends on the LED too…

Merely my subjective opinion, but I find 5000-5500k most pleasant; the 6500K LEDs I have are too blue for me.

Scarodactyl wrote: ↑

Mon Feb 13, 2023 8:43 pm

The simplest approach is probably a buckblock, the main downside being they max out at 2100ma so you can't drive e.g. a Cree XP-L at full power, but they still run very bright. Otherwise implementation is incredibly easy.

Agreed. I'm not very skilled when it comes to electronics and I found the 2100ma buckblock with the 0-10v dimming circuit easy and reliable. link to my LED conversions

If they ever make a 3amp buckblock I'll be first in line.

Scarodactyl wrote: ↑

Mon Feb 13, 2023 10:19 pm

If they ever make a 3amp buckblock I'll be first in line.

https://www.amazon.com/dp/B07J9RQ8B6/

Thanks! I will take a look at that.
I actually sent an email shortly after making the post and apparently a 3000ma buckblock is in the works which is ni e.

Scarodactyl wrote: ↑

Tue Feb 14, 2023 6:29 pm

I will take a look at that.

It is has both constant voltage and current 10-turn pots;
one comfortable with soldering could replace a 10-turn pot with a remote single turn control.
I use one to supply a substantial supercapacitor bank, which takes several minutes to charge at about 4.5 amps,
during which time the buck heatsink gets warm but not dangerously.

blekenbleu wrote: ↑

Wed Feb 15, 2023 10:07 am

Scarodactyl wrote: ↑

Tue Feb 14, 2023 6:29 pm

I will take a look at that.

It is has both constant voltage and current 10-turn pots;
one comfortable with soldering could replace a 10-turn pot with a remote single turn control....

That might not be a bad idea as those small, PCB trimpots are typically rated for only a couple hundred rotations.