Analog Dimming w/ Meanwell LDD-L (prototype) - The Planted Tank Forum
 1Likes
Reply
 
LinkBack Thread Tools Display Modes
post #1 of 16 (permalink) Old 08-13-2017, 02:34 PM Thread Starter
Wannabe Guru
 
PTrader: (0/0%)
Join Date: May 2017
Posts: 1,698
Analog Dimming w/ Meanwell LDD-L (prototype)

I built this prototype to see if analog dimming is viable way to adjust output. Circuit uses a 12V,5A supply, LDD-1200L, a $1 BuckConverter (Buck^2 Converter) from the bay, and a linear 18K potentiometer.

The led array is 2x2. Buck converter and pot used to create a variable 0-2.5 voltage.

The circuit is quite functional, with some caveats. The only real problem is that the Meanwell LDD can only be dimmed within range of 20-100%. Once the voltage from the pot drops below .5V, the leds turn off. Bottom fifth of sweep is off.

Subjectively, I would say that the dimming is roughly linear, but the jump from 0-20% is quite annoying. If I can devise a way to keep the lower limit of the pot to .5V, then it will be much more user friendly.

That said, the best application for this analog dimming would be in nano tanks with small arrays, to perfectly balance color ratios. A 12v, 5A supply could run four channels of 4x 3W leds, using 4x LDD1200Ls. WRGB Larger arrays can adjust balance by changing the relative numbers of leds.

Note: As this is a prototype, I did not build a current mirror to protect the leds.
Attached Thumbnails
Click image for larger version

Name:	20170813_100614 (1).jpg
Views:	160
Size:	34.4 KB
ID:	780769  

ChrisX is offline  
Sponsored Links
Advertisement
 
post #2 of 16 (permalink) Old 08-13-2017, 07:06 PM
Planted Member
 
Lingwendil's Avatar
 
PTrader: (0/0%)
Join Date: Nov 2012
Location: Oakley, Ca
Posts: 246
Stick a 1n4148 diode on the ground leg of the pot to get close to .7v (like, .65 volt or so) to get a bit better resolution or a schottky or even old-school germanium diode for a lower drop, or do a bit of math to use a resistor there as a resistor divider, for example if you are using a 18k pot, math points to 20% being at 4.5k, so you can use an easy to find 4.7k resistor to get you close enough for our purposes.

I was actually getting ready to build something similar for the LDD-1000L's that have on the way for my reef tank. Would be nice to be able to fine tune the brightness without a full controller.

Alternatively, Theatrus makes a nice two-channel driver that is compatible with 3.3v-5v PWM, and is adjustable from 400-1000mA via the onboard pot-

Acrostar AcroIQ drivers

Just a few bucks more than a pair of LDD-1000L drivers, adjustable, comes with solderless connectors, and easily mounts to a heatsink. Pretty nice little products.

Last edited by Lingwendil; 08-13-2017 at 07:14 PM. Reason: edit
Lingwendil is offline  
post #3 of 16 (permalink) Old 08-13-2017, 08:25 PM Thread Starter
Wannabe Guru
 
PTrader: (0/0%)
Join Date: May 2017
Posts: 1,698
Quote:
Originally Posted by Lingwendil View Post
Stick a 1n4148 diode on the ground leg of the pot to get close to .7v (like, .65 volt or so) to get a bit better resolution or a schottky or even old-school germanium diode for a lower drop, or do a bit of math to use a resistor there as a resistor divider, for example if you are using a 18k pot, math points to 20% being at 4.5k, so you can use an easy to find 4.7k resistor to get you close enough for our purposes.

I was actually getting ready to build something similar for the LDD-1000L's that have on the way for my reef tank. Would be nice to be able to fine tune the brightness without a full controller.

Alternatively, Theatrus makes a nice two-channel driver that is compatible with 3.3v-5v PWM, and is adjustable from 400-1000mA via the onboard pot-

Acrostar AcroIQ drivers

Just a few bucks more than a pair of LDD-1000L drivers, adjustable, comes with solderless connectors, and easily mounts to a heatsink. Pretty nice little products.
Thanks! I searched google earlier and realized I needed to put a resistor on the ground leg, but the math wasn't clear. Theres a site with a calculator and it seems like the Vmax influences the resistor choice.

The other problem is that I ordered pots/knobs from ebay, but they have intermittent contacts and can't be used. I resorted to using a pot from my old guitar parts box, but I dont have multiples of the same value, which means the math (performance) would be different for each channel. I also would need to order resistors or scavenge from old routers or other outdated tech.

Another possibility is using another pot to "find" the resistance I'm looking for.
ChrisX is offline  
 
post #4 of 16 (permalink) Old 08-14-2017, 01:09 AM
Planted Member
 
Lingwendil's Avatar
 
PTrader: (0/0%)
Join Date: Nov 2012
Location: Oakley, Ca
Posts: 246
For the current that you are dealing with the size isn't influenced much by the supply voltage, and the dim pin on the LDD doesn't draw any appreciable amount of current. Could even run a pot across a zener (or a regular 5mm LED of the right voltage instead of the zener) diode shunt regulator that is fed off of the main LED supply voltage, with a pot across the zener to set the current, then you can lose the buck power supply feeding the pot. Saves a buck or two, and less wiring, but now you're getting silly if you go that way...
Lingwendil is offline  
post #5 of 16 (permalink) Old 08-14-2017, 01:44 AM
Planted Tank Guru
 
PTrader: (0/0%)
Join Date: Jun 2013
Location: WI
Posts: 10,838
REally can't quite grasp why you just don't get some of these:
PWM Dimming Controller For LED Lights or Ribbon 12 Volt 8 AmpAdjustable Brightness Light Switch Dimmer Controller DC12V 8A 96W for Led Strip Light 5514243 2017 ? $3.74

solder a wire to the gate of the internal MOSFET and be done w/ it..
0-100% dim w/ a 12v DC wall wart to power them..

Output is approx 5V and 900Hz on the gate leg..
https://www.plantedtank.net/forums/20...mer-ldd-h.html
Seems like a LOT of effort to save a dollar or 2......

"A man with a watch knows what time it is. A man with two watches is never sure."
jeffkrol is online now  
post #6 of 16 (permalink) Old 08-14-2017, 01:45 AM Thread Starter
Wannabe Guru
 
PTrader: (0/0%)
Join Date: May 2017
Posts: 1,698
I found the formula for the resistors to set min and max values. Just have to find resistors to match the pots i have on hand...

I was going to use an lm317 v regulator, then i saw buck converters were 5 for $5..no brainer.

The analog control elements for an ldd channel cost is negligible.

I received the leds today, have parts for current mirror. If i can find the right resistors i wont have to order anything. Full version might get built in a few days.

Quote:
Originally Posted by jeffkrol View Post
REally can't quite grasp why you just don't get some of these:
PWM Dimming Controller For LED Lights or Ribbon 12 Volt 8 AmpAdjustable Brightness Light Switch Dimmer Controller DC12V 8A 96W for Led Strip Light 5514243 2017 ? $3.74

solder a wire to the gate of the internal MOSFET and be done w/ it..
0-100% dim w/ a 12v DC wall wart to power them..

Output is approx 5V and 900Hz on the gate leg..
https://www.plantedtank.net/forums/20...mer-ldd-h.html
Seems like a LOT of effort to save a dollar or 2......
Form factor, time, and cost. Shipping from china, and real estate on my light bar. Its not clear that 4 of each color led will be enough, i may need a larger supply, which means id need the buck converter anyway to control the pwm.

So basically we are comparing $4 a channel (will need 6 = $24) plus shippping time from china, against pots and resistors i may already have. Also i can cluster the pots together in a nice rgb control group. This is how i envisioned it. Giving up the bottom 20% of range is probably not a big deal. Plus theres no room for them on the back of light bar.

Last edited by Darkblade48; 08-14-2017 at 10:17 AM. Reason: Please use the edit function for back to back posts to keep threads cleaner
ChrisX is offline  
post #7 of 16 (permalink) Old 08-14-2017, 03:10 AM
Wannabe Guru
 
PTrader: (0/0%)
Join Date: Jun 2017
Posts: 1,041
You can get everything you are looking from Digikey.com or Mouser.com. You don't have to go to china for electronic components. And sometimes Chines parts are unreliable or don't provide accurate specifications for what they sell.
Surf is offline  
post #8 of 16 (permalink) Old 08-14-2017, 04:23 AM
Planted Tank Guru
 
PTrader: (0/0%)
Join Date: Jun 2013
Location: WI
Posts: 10,838
Quote:
Originally Posted by ChrisX View Post
Form factor, time, and cost. Shipping from china, and real estate on my light bar. Its not clear that 4 of each color led will be enough, i may need a larger supply, which means id need the buck converter anyway to control the pwm.
Then just build one on 555 timing chips..


Skip the transistor ect.. Sure you can get 5v PWM out of (3)
Use 5v in..

http://www.talkingelectronics.com/pr...0Projects.html
http://www.circuitsgallery.com/2013/...ed-dimmer.html
555 timing chips are like 25 cents..
Quote:
Originally Posted by ChrisX View Post
So basically we are comparing $4 a channel (will need 6 = $24) plus shippping time from china, against pots and resistors i may already have. Also i can cluster the pots together in a nice rgb control group. This is how i envisioned it. Giving up the bottom 20% of range is probably not a big deal. Plus theres no room for them on the back of light bar.
Yea I get that.. parts on hand and room..
Still..

This is for myself.. S

"A man with a watch knows what time it is. A man with two watches is never sure."

Last edited by jeffkrol; 08-14-2017 at 04:48 AM. Reason: edit
jeffkrol is online now  
post #9 of 16 (permalink) Old 08-14-2017, 12:57 PM
Planted Member
 
Lingwendil's Avatar
 
PTrader: (0/0%)
Join Date: Nov 2012
Location: Oakley, Ca
Posts: 246
Quote:
Originally Posted by jeffkrol View Post
Then just build one on 555 timing chips..


Skip the transistor ect.. Sure you can get 5v PWM out of (3)
Use 5v in..

30 LED Projects
PWM LED Dimmer/ Brightness Control by 555 Timer With Video Simulation - Circuits Gallery
555 timing chips are like 25 cents..


Yea I get that.. parts on hand and room..
Still..

This is for myself.. S
I've got a schematic put away somewhere that does the same thing with dual op-amps, and works pretty well. I come from the DIY hi-fi/audiophile side of things so I've got a great big pile of dual op-amps, pots, resistors, you name it to play with, I might throw one together.
Lingwendil is offline  
post #10 of 16 (permalink) Old 08-14-2017, 02:01 PM Thread Starter
Wannabe Guru
 
PTrader: (0/0%)
Join Date: May 2017
Posts: 1,698
So many ways to skin a cat...

Using analog pots to control LDD dimming probably ranks with the cheapest and simplest. Less points of failure, etc.. I'm surprised no one else has pursued this.

I think many people who are building their own lights are probably thinking "biggest and best" and the possibility of doing it this way either escapes their notice or is dismissed.
ChrisX is offline  
post #11 of 16 (permalink) Old 08-14-2017, 02:51 PM
Planted Tank Guru
 
PTrader: (0/0%)
Join Date: Jun 2013
Location: WI
Posts: 10,838
0-10V analog dimming is an industry standard..
$3 manual 555/MOSFET dimmer certainly isn't "biggest and best"...

now a $549 Apex controller w/ analog relay outlets and 0-10V analog dimming is another story..
http://www.bulkreefsupply.com/apex-c...SABEgIYo_D_BwE

"A man with a watch knows what time it is. A man with two watches is never sure."
jeffkrol is online now  
post #12 of 16 (permalink) Old 08-14-2017, 03:11 PM Thread Starter
Wannabe Guru
 
PTrader: (0/0%)
Join Date: May 2017
Posts: 1,698
Quote:
Originally Posted by jeffkrol View Post
0-10V analog dimming is an industry standard..
$3 manual 555/MOSFET dimmer certainly isn't "biggest and best"...

now a $549 Apex controller w/ analog relay outlets and 0-10V analog dimming is another story..
Apex Classic Controller with Lab-Grade pH Probe - Neptune Systems - Bulk Reef Supply

I dont think you understand my goals. Getting 2x the PAR and RGB adjustment for half the cost of low end commercial offerings, that can be installed in my existing light bars. If I blow another $3-5 per channel then I stray farther from my goal.

Spending another $3-5 on each channel, it has already funded a TC420. Plus the build complexity. So thats a non starter. I dont need the 0-20% adjustment range unless I have a programmable unit to do things like sunrise/sunset/moonlight. The RGB adjustment is to allow me to alter the intensity of the colors to match the output of the adjustable whites. The design is also influenced by leftover parts I already have.

My plant growth is crazy, I think I've got the PAR, now I've got to get the CRI. Thanks for your guidance.

BTW, I'm using the same color ratios as that guy with the SdiyN custom build, minus the WW.
ChrisX is offline  
post #13 of 16 (permalink) Old 08-14-2017, 03:49 PM
Planted Tank Guru
 
PTrader: (0/0%)
Join Date: Jun 2013
Location: WI
Posts: 10,838
Quote:
Originally Posted by ChrisX View Post
I dont think you understand my goals. Getting 2x the PAR and RGB adjustment for half the cost of low end commercial offerings, that can be installed in my existing light bars. If I blow another $3-5 per channel then I stray farther from my goal.

Spending another $3-5 on each channel, it has already funded a TC420. Plus the build complexity. So thats a non starter. I dont need the 0-20% adjustment range unless I have a programmable unit to do things like sunrise/sunset/moonlight. The RGB adjustment is to allow me to alter the intensity of the colors to match the output of the adjustable whites. The design is also influenced by leftover parts I already have.

My plant growth is crazy, I think I've got the PAR, now I've got to get the CRI. Thanks for your guidance.

BTW, I'm using the same color ratios as that guy with the SdiyN custom build, minus the WW.
No, I understand .. Just like to poke once and awhile..

always tradeoffs.. This was a fun one for example:
Radions vs Chinese LEDs - Reef Central Online Community
Quote:
Probably about 200-220 total. Oh power supply, 28 so say 240. Cost per twin light unit approx 80. Compared to 500 for Radion.

"A man with a watch knows what time it is. A man with two watches is never sure."
jeffkrol is online now  
post #14 of 16 (permalink) Old 08-14-2017, 07:32 PM Thread Starter
Wannabe Guru
 
PTrader: (0/0%)
Join Date: May 2017
Posts: 1,698
OK.. just figured out a simple way to limit the pot's sweep to stay within the .5-2.5V range.

The equation to determine the resistor value you need on the ground leg of the pot is:

R / ( 500KOhms + R) = .20

...

R = 125KOhms

In this example, I am using a 500K pot and I want the lower voltage to be limited to 20% of Vmax.




I didn't have any resistors in the correct values to match my pots, but like any long term guitar player, I have a TON of old pots from past wiring projects. In fact, most of them are 250K and 500K (typical pots used in passive guitar wiring.)

Guitar Player's Solution:

So the solution is to use a 500K pot for the adjustment, and use a 250K pot on the ground leg to set the Vmin. 125K is roughly in the middle of the adjustment range of the 250K pot, so it's easy to dial in. This has the additional benefit that it doesn't rely on just math to get the correct resistance.

You can dial it in so that the sweep goes from .5 to 2.5V, or you can set it so the low voltage is .49V if you want an off without wasting any of the sweep range.

I'd say thats better than waiting a month for parts from China.
Attached Thumbnails
Click image for larger version

Name:	20170814_151728.jpg
Views:	79
Size:	43.7 KB
ID:	781081  

ChrisX is offline  
post #15 of 16 (permalink) Old 05-08-2019, 03:40 AM
Newbie
 
PTrader: (0/0%)
Join Date: May 2019
Posts: 1
ChrisX, what's the BuckConverter model you used in your circuit? Would a DC-DC LM2596 Buck Converter step-down module work?
FredML is offline  
Reply

Tags
None

Quick Reply
Message:
Options

Register Now



In order to be able to post messages on the The Planted Tank Forum forums, you must first register.
Please enter your desired user name, your email address and other required details in the form below.

User Name:
Password
Please enter a password for your user account. Note that passwords are case-sensitive.

Password:


Confirm Password:
Email Address
Please enter a valid email address for yourself.

Email Address:
OR

Log-in










Thread Tools
Show Printable Version Show Printable Version
Email this Page Email this Page
Display Modes
Linear Mode Linear Mode



Posting Rules  
You may post new threads
You may post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On

 
For the best viewing experience please update your browser to Google Chrome