[chbot] In need of dimmer board to control 12v LED via Arduino

Mon Jan 29 07:44:44 GMT 2018

Hi Mike,

The 24V LED lights dim fine.

How many prototypes are you thinking about?

Will call to sort out how to get money to your account.

Kind Regards,
Rob 

From: Mike Field [mailto:hamster at snap.net.nz] 
Sent: 28 January 2018 23:24
Subject: Re: [chbot] In need of dimmer board to control 12v LED via Arduino

Hi Andrew,

Well, I've got a breadboarded example going, with a couple of Jaycar SOIC8  Dual MOSFETs and the PWM controller of an ESP32 - see it in action at https://www.youtube.com/audio?video_referrer=watch <https://www.youtube.com/audio?video_referrer=watch&v=g-KZkL_qF9g> &v=g-KZkL_qF9g if interested.

A few thoughts/ideas came along the way:

- If a microcontroller is on each board, the power soon adds up - Something with WIFI would need about 150mA @ 3V3 - or about 0.5W doing nothing (or about 2W if using a linear regulator from 12V). A few of them around the place going 24x7 will quickly consume significant power. So it makes more sense to have the PWM board dumb, connecting back to a single controller.

- Cat6 has a resistance of approx 12.5 ohms per 100 m. Five meters of cable with a dead short would be 1.25 ohm (0.625 there, 0.625 back) so at 12V a dead short will give about 9.6A - not enough to blow a single 10A fuse (which allows for 120W of load per PCB). So safety first, an appropriate fuse for each channel is needed. 

- Also, the current draw along longish cables will cause a different in GND between the controller and the PWM board. With a small difference the microcontroller would not be able to full switch the MOSFET fully on, causing the magic smoke to get out. Optoisolators can resolve this, and improve safety & reliability.

- Rob discovered that he has 24V LEDs. The parts randomly chosen are 60V MOSFETS (SI4946DY), and 10V-30V Optoisolators/Mostfet drivers (TLP701).  It halves the current for the same wattage load, which is good for voltage drops and overall efficiency.

- Adding footprints for snubber diodes across the outputs would allow it to drive inductive loads without popping things (not added to PCB yet)

- Swapping pin headers with a RJ45 footprint for easy & reliable connectivity back to the controller seems to be a good idea 

I've got a brief sketch of a PCB (note to self, pinout for the opto is wrong), just checking that things fit into a $1 100mm x 100mm PCB. A proper layout will need to wait till the parts arrive and footprints can be verified. 

Prices at Ali Express work out to be about NZ$10 per board, incl PCB (or $1.66 per channel) - I've got a shopping cart ready to go for all the bits I don't have to hand for a few prototypes, but am waiting to verify that the LEDs will actually dim properly before spending pocket money.

Mike

On 28/01/2018 7:46 PM, Andrew Sands wrote:

Guys,

Anyway to get in on this as a discussion. I may not be able to bring much to the table but I can 'break' things?

regards,

Andrew

On Wed, Jan 17, 2018, at 20:06, Rob de Voer wrote:

Hello Mike,

Yes, a design based on Mosfets seems to be best way to go.

How do you use the RGB strips? Still on your workbench or installed in your house?

Have some step down regulators to convert the 12v to 3.3or 5v and can also bring ESP32, Arduino and WemosD1 R2 as alternatives to drive the gate.

Would be great to get together and sort this out.

I have no relevant experience with any PCB design work (am a mechanical engineer with 30+ years of software development experience), played around in Fritzing to create my designs but never turned any of those into PCBs.

The couple of boards I made consist of soldered tracks on test boards…

Will email my contact details offline to arrange getting together.

Kind Regards,
Rob

From: Mike Field [mailto:hamster at snap.net.nz] 
Sent: 17 January 2018 22:38
To: Rob de Voer  <mailto:rob at businesspalz.com> <rob at businesspalz.com>
Subject: Re: [chbot] In need of dimmer board to control 12v LED via Arduino

Hi Rob,

I am switching 25W 12V RGB strips using Si4944DY 30V Dual MOSFETS from Jaycar - datasheet is at https://www.vishay.com/docs/72512/72512.pdf  They are tiny SOIC8 packages, and can switch about 10A (!)

'On' resistance is less than 0.02 Ohm, These are old parts, the replacement Si4946 are rated at 60V. I've got 10 of these on their way from my mate Ali E in China for $1 each :-)

I've got a couple mounted on DIP adapters, on a breadboard with an ESP32 driving the gate through a current limiting resistor.  You are more than welcome pop over and either experiment with them - I can hook your load up to a PSU and a function generator driving the gate), or take one away to play with.

I'm also happy to work with you on a board, with headers for the ESP module, 6(?) channels (3 dual MOSFETS), screw terminals and so on. We could even add a 5V0 or 3V3 regulator to power whatever is controlling the lights. I'll got all the bits here or almost here, just not enough motivation to move it off the breadboard to  a PCB. - fancy a Saturday afternoon / evening project session?

Are you better at KiCad or Eagle than me?

Mike.

On 17/01/2018 10:02 PM, Rob de Voer wrote:

Hi All,

I have been gradually replacing the 240v lighting in my house with 12v LED lights all powered by one 12v transformer and switched through a home automation system made up of several Arduino boards and one RaspBerryPI3.

I want to start installing higher powered LEDs (21w 12v or more), dim them to the low output for daily needs, and adjust the dimmer as needed.

Unfortunately building a suitable dimmer module so I can control individual LED lights has thus far proven outside of my ability.

Have tried some of the published designs but have to resign myself to the fact that I should stick to building software since i appear unable to convert any of the myriad of example project to my needs.

Who is able to help me build a 12v dimmer board that can be controlled remotely using any of  Arduino / ESP8266 / WemosD1R2? 

Do I need to limit myself to a specific power (i.e. 21w LED) for the dimmer to work efficiently or is a good design not that restrictive?

Kind Regards,

Rob

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