Programmable Dimming for Constant Current LED driver (SOLVED) - Page 1
Forum section: electronics / beginners

author: MephistoRolling
author_rank: Newbie
timestamp: March 19, 2015, 09:08:59 am
content: Hey everyone, First time posting here.I am creating a lighting system for a vivarium and want the leds to fade in and out during the day.I bought 5 of thesehttp://www.ebay.com.au/itm/18W-CBUS-SAA-DIMMABLE-700mA-LED-DRIVER-CONSTANT-CURRENT-POWER-SUPPLY-TRANSFORMER-/131143548831?pt=LH_DefaultDomain_15&var=&hash=item1e88c3bf9fThe dimming part says 0-10v so i created a programmable 0-10v supply using an op amp and an at tiny.It can output the voltage i want.... but it doesn't seem to work on the drivers.I WORKED OUT WHY... the 0-10v is the amount running through these pins that need to be dimmed (ACTUAL VOTAGE IS 11.6)... so i wasted a lot of time and effort already.It mentions leading edge and trailing edge dimmers, so now i am starting to think its not a 0-10v dimmer and instead requires one of those types of dimmers instead.I am kind of stuck, as i went through a lot of work to make the Positive/Negative power supply and the OPamp and tiny stuff. and now i realise it was all wasted effort.NOW TO MY QUESTIONS.Is there a way to make a programmable dimmer that will work with this? If you can give any advice, info, schematics, anything it would be great. i learn fast and am willing to make any circuits i need.

author: Rerouter
author_rank: Super Contributor
timestamp: March 19, 2015, 09:52:56 am
content: cbus is a data protocol, its not just a control voltage, so you would have to look up what kind of data it expects,The leading / lagging dimming is from a conventional dimmer to the supply of the driver, in this case aim for interfacing via cbus,

author: MephistoRolling
author_rank: Newbie
timestamp: March 20, 2015, 11:37:05 am
content: http://www.winpsen.com.cn/en/default.asp?id=1823Here is more info on the driver.It says it can accept 0-10v analog and pwm C-bus.I cant find info on what the c-bus systems output or how they work.all i can find is on the programming and system side of things, not the end output.What i dont get about the 0-10v idea is that the dimming contacts are already running a positive voltage, so it seems you have to reduce this voltage rather then supply it, to dim the lights.I tried dimming the voltage with a mosfet and it seems to work a bit, but not properly. will keep fiddling with that idea for now.http://www2.clipsal.com/cis/__data/page/428/5504AMP%20Series%20%20C-Bus%20Four%20Channel%20Analogue%20Output%20Unit%20Installation%20Instructions2.pdfhere is some data on a C-BUS 0-10V unit....I dont understand if the output is 0-10v why is there already power running through the lines. why does it need to supply power when the connections it is going to already have a voltage running through it.

author: Corporate666
author_rank: Unknown
timestamp: March 20, 2015, 12:22:54 pm
content: Quote from: MephistoRolling on March 20, 2015, 11:37:05 amI am not really familiar with C-Bus... looks like it's more used in Europe and Oz, and I don't see a ton of documentation for it online. Anyway... from my reading of the specs of your driver, it will accept 0-10V *OR* PWM via C-Bus, so you don't need to provide the 0-10V via C-Bus, you can just do 0-10V directly.They really should have a datasheet on the website.. I'd perhaps email them and ask. However, that aside.... the driver mentions "intelligent dimming methods" or something, where it will recognize either 0-10V or a C-Bus connection... so perhaps the voltage you are measuring is actually a DC average by a comparatively slow multimeter of a communication signal. And perhaps also the unit is alternately sending some kind of handshake for C-Bus and measuring voltage incoming.I've seen plenty of drivers that will operate with simply an external trimpot to set the voltage (by dividing down an output voltage). So I'd try shorting the pins of the dimming output and see if the output turns off. If so, I'd connect up a pot to let you vary between 0V and the max voltage - see if you then get a linear dimming output. If so, then you have your answer.You didn't really say what you mean by "I tried a MOSFET and it kind of works but not correctly".

author: Rufus
author_rank: Super Contributor
timestamp: March 20, 2015, 12:39:55 pm
content: Quote from: MephistoRolling on March 20, 2015, 11:37:05 amThe 0-10v dimming input needs to be pulled up internally to a voltage of at least 10v otherwise the driver output would be completely dimmed when no connection is made to the dimming input.The dimming input when driven by a voltage will source current.As with most cheap Chinese crap documentation is almost non-existent.It sounds like the dimming input can also be driven by a 0-10v PWM signal - it probably just includes an RC low pass filter on the input so the PWM is averaged to a voltage.

author: MephistoRolling
author_rank: Newbie
timestamp: March 20, 2015, 01:24:48 pm
content: I managed to get the lights to dim properly by modulating the voltage going through the C- and C+ lines.Using an attiny85 to send the signal to the gate of an IRF640A (Mosfet) i pulled off an old MotherBoard.The reason why it was only KINDA working when i tried it the first time was to do with my wire gauge being too thin. and also the ATTINY 85 can run at 1mhz and 8mhz and the timings of the changes on the different frequencies didn't give the transformer time to adjust with the delay settings i was using. There is a delay between the gate signal and the actual lights dimming, i am guessing due to some capacitance inside the driver.It all seems to be working now.Thanks for your input.