interfacing a CCS to a pic

[large_ghostman]

LEDs in series driven by a constant current source don't need to be well matched. The current through each LED will be exactly the same, regardless of Vf. The brightness may vary if they're not well matched. Power dissipation will vary too as Vf varies, but this shouldn't be an issue unless they are being driven at max power.

Opto-isolators are a good idea (provided they are placed in the right location) but you don't need an additional transistor to drive the module input pin that's designed to be driven by a microcontroller output. The output of the optoisolator is a transistor.

MrDEB hasn't said if he's planning to drive the modules with PWM to have brightness control. If that's his plan, I'm looking forward to seeing how he's going to drive ten(?) modules with a PIC18F-series.

Some where PWm for brightness is mentioned, so i have been advocating PWM on the GND. But hey its a Mr Deb thread, therefore the normal laws of physics are suspended until further notice.

 

[large_ghostman]

How big is the board your building your toaster on?

 

[JonSea]

LGM,

The one certainty in a MrDEB thread...whatever you are commenting on has nothing to do with the plan now.

 

[large_ghostman]

No one told me there was a PLAN!!!

 

[JonSea]

It's a secret plan. Not just anybody gets to see it.

 

[be80be]

LOL Jon

 

[MrDEB]

the leds are to be mounted using a heat sink on a section of wood.
Yes the plan has changed from using mosfets to 2n3904 transistors and a CCS module.
going to call the module supplier on Monday to double check on the module specs and number of recommended lrds etc.

 

[large_ghostman]

the leds are to be mounted using a heat sink on a section of wood.
Yes the plan has changed from using mosfets to 2n3904 transistors and a CCS module.
going to call the module supplier on Monday to double check on the module specs and number of recommended lrds etc.

Call them Tuesday, no point messing up their whole week! no one likes a hard Monday

 

[MrDEB]

I saw a post by LGM using silicone glue to hold SMD parts to a board. I tried using crazy glue with good success. Just be sure to swipe some flux (Chip-Quik) on the pads before gluing. IMO it tends to make the solder flow in, around and under while soldering. Tried with out and didn't look as good and had to touch up some of the pins on a pic.

 

[large_ghostman]

Silicon Glue??

NO high temp Silicon GREASE

This type of stuff
**broken link removed**

Means no solder will stick to it and it dosnt melt with a soldering iron, I use it on the ultra small smd resistors etc. I put it between the pabs to stop solder bridges under the resistor.

 

[JonSea]

Silicon Glue??

NO high temp Silicon GREASE

This type of stuff
**broken link removed**

Means no solder will stick to it and it dosnt melt with a soldering iron, I use it on the ultra small smd resistors etc. I put it between the pabs to stop solder bridges under the resistor.

That's a critical difference. Silicon grease conducts heat. Silicon glue is an insulator.

Superglue sounds like a really bad idea too. It's stiff and rigid. As the circuit board flexes and changes temperature, that will put stress on the components. Solder joints will Crack or components will fracture. SMT components don't lend themselves to inventive ways of handling.

 

[large_ghostman]

That's a critical difference. Silicon grease conducts heat. Silicon glue is an insulator.

Superglue sounds like a really bad idea too. It's stiff and rigid. As the circuit board flexes and changes temperature, that will put stress on the components. Solder joints will Crack or components will fracture. SMT components don't lend themselves to inventive ways of handling.

That stuff dosnt conduct, I even gave the make when I said before. It is used in chemistry alot for things like distillations, give it a few mins to evap off some fumes and its good to go. I havnt tried any other brands so ni idea if they work, the down corning stuff costs alot but no home should be without .

Getting any residue off is a utter nightmare, the only chemical I found that will begin to remove it is Trichlro.....Almost everything else bounces off it

 

[be80be]

The data sheet said it's a insulator

 

[JonSea]

I said it conducts heat. Sorry for the confusion.

 

[be80be]

You can buy the same stuff at home depot. I would think solder paste would be all you need and rework station or hot plate.

 

[large_ghostman]

That's a critical difference. Silicon grease conducts heat. Silicon glue is an insulator.

Superglue sounds like a really bad idea too. It's stiff and rigid. As the circuit board flexes and changes temperature, that will put stress on the components. Solder joints will Crack or components will fracture. SMT components don't lend themselves to inventive ways of handling.

I still read it wrong . Word association in play , conducts on an electronics form............ Off to write out 200 X 'I must read the whole sentence properly, before opening my mouth '

Burt I use it for chemistry and things like distilling conc Nitric acid, I would never trust any other brand. So I have no experience with ones, so I can only vouch for that one. Plus we dont have a home depot in the UK (well not that I know off), I would of thought that most similar ones would work for this application. Considering the kind of stuff I normally use it for, I would dream of trying something else .

Pulling a vacuum on 96% Sulphuric acid while distilling of another 2% water, is a bit bum twitchy to say the least .

 

[be80be]

I was just saying for holding resistors they have some in the plumbing its for setting o rings

 

[large_ghostman]

I was just saying for holding resistors they have some in the plumbing its for setting o rings

I might give another brand a go for this, the down corning stuff I treat like gold, the tube comes 3/4 empty! But for heavy duty chemistry I would trust anything else. A cheap alternative for soldering the ultra small smd stuff would be good, then I can keep my precious for its intended purpose .

 

[be80be]

Silicone Grease 1/2 Oz,
from Walmart - Life and Home

12 product reviews

Silicone Grease - Resistant to most harsh chemicals. Retains its consistency in temperatures from -40 deg. to 400 deg. Odorless scent makes this product easy to work with ...Walmart - Life and Home

It's in tube at home depot it's tackie and keeps stuff in place hard to wash off great for O rings.
I'm sure it would hold a smt part in place but solder paste works good too.

 

[large_ghostman]

Yeah not a chance I would use it in the chemistry lab .