computer Christmas lights

[MrDEB]

years ago I assembled a Compurterized Christmas light display but since sold the entire setup.
I recall the SSR or triac boards used an opti-isolator, couple resistors but instead of using a computer, I want to just use a PIC to drive the opti_isolator. Just started looking for leftover plans and parts but figure would ask first.

 

[MrDEB]

OUPS your pic has the DRAIN with a heat sink. Looking for a heat sink in Diptrace or something useful.

 

[For The Popcorn]

It's just a copper area. There's not some footprint for it.

There's a ground plane on the bottom side of the board under the mosets. I could have added copper areas around the drain connections and stitched them to the ground plane, but the large trace and via to ground plane will conduct heat away.

Don't skimp on trace width anyway. There's nothing be be gained where there's plenty of room.

 

[MrDEB]

I think I discovered a way to insert a heat sink under the DRAIN pin.
Just place a larger pin under the DRAIN pin and add a large copper area under the mosfets and tie the two together.
Going to wait for the SMD MOSFETS before finishing the design.
Thanks

 

[For The Popcorn]

That doesn't sound like a very good approach.

Figure out how to make a copper area and connect it to the net.

 

[MrDEB]

I think I can just include it in the same net. Will try that.
Curious, in your pic post #99 what is with all the holes?
Thinking of a heat sink copper area under the SOURCE pin as well?











i can just includ

 

[MrDEB]

got it. Just use an OBJECT pad, change the size and include in the same net as the DRAIN pin.

 

[For The Popcorn]

The holes about the mosfets are vias to the ground plane – large diameter to handle a lot of current.

The pads below the mosfets are for a terminal block.

Ground plane is under all of it.

 

[MrDEB]

while waiting for parts I decided to start installing the LED / NEON strips. Boy are they hard to solder. Using wire wrap wire (30agw?) curious what amperage is this wire good for?

 

[For The Popcorn]

If only there was some way to find out.... it may make a nice fuse if there's any length involved.

Big Clive likes soldering not to the end pads but to a non-cut set. This might be easier.

 

[MrDEB]

the strips I am soldering have a silicone cover that must be cut to gain access to the pads.

 

[MrDEB]

here is a picture of the strips I am working with. Very hard to solder, but I discovered that using a larger diameter solder works, but using low temp solder paste works even better. The silicone covering melts really easily.

 

[MrDEB]

been coming up with an additional "automation" for my art project. I needed a cake so why not add some sprinkles to the birthday cake. I have the 560 ohm resistor arrays and the mosfets so here is what I came up with. IMO it should work?

 

[For The Popcorn]

"IMO" your schematic shows a p-channel mosfet, while calling out an SSM3K341R, which is an n-channel mosfet, so likely neither is accurate. So what mind reader can say if your circuit will work?

 

[tumbleweed]

I have the 560 ohm resistor arrays and the mosfets so here is what I came up with. IMO it should work?

You'll likely find that the different color LEDs want to have different resistor values, for at least a few of them.
They're usually very different in terms of brightness and forward voltage drop.

 

[MrDEB]

It is an N channel MOSFET. I grabbed the wrong schematic MOSFET.
As far as brightness I think I only have the 560 ohm arrays but maybe some 130's?
good catch thanks

 

[ChrisP58]

It is an N channel MOSFET. I grabbed the wrong schematic MOSFET.
As far as brightness I think I only have the 560 ohm arrays but maybe some 130's?
good catch thanks

I think that the point that tumbleweed was making, is that you may want a different resistor value for each LED to adjust for the different Vf and brightness of the different color LEDs.

Using a resistor array prevents you from doing that.

 

[MrDEB]

I realize that the different resistors will change the brightness.
In my application, I have 12 SMD LED's glued to 1/8" white plexiglass so the LEDs shine through the plastic. These are "sprinkles" on a white birthday cake for our town's centennial celebration
Question? on DMM diode readings.
BLUE = 2.40
GREEN = 2.25
RED = 1.72
WHITE = 2.56
My thinking is these readings correlate with the forward voltage of the LED?
note these LEDs are planned to connect as per post#112

 

[For The Popcorn]

Yes.

 

[For The Popcorn]

Do be aware that just running the same current through each LED (by adjusting each LED's resistor) probably won't give anything approaching uniform brightness. You need to put them side-by-side and adjust the resistor values until the brightness appears uniform by eye. The blue will likely need the least current, the red the most.

 

[tumbleweed]

I agree... plus it really depends on the exact LEDs you choose. I've had blue LEDs that would blow your eyes out with just a couple of mA's.

BLUE = 2.40
...
WHITE = 2.56

Those numbers look suspiciously low to me.