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Topic: Boosting Logic Voltage (LED Strips on Teensy) (Read 7691 times) previous topic - next topic

Qdeathstar

A creaking creeping shadow
stiff against the freezing fog
glares at a tickless watch.

Time has failed him -- all things shall pass.

Wawa

#31
Jul 15, 2015, 01:34 am Last Edit: Jul 15, 2015, 01:56 am by Wawa
The LPD8806 datasheet states "supporting LED lighting voltage upto 12volt" and "Absolute max of 5.5volt ".
There must be a voltage regulator for the IC on the strip.
The datasheet has a 5.1volt zener diode from VCC to ground.

Here is the Adafruit version. It needs a 5volt supply.
http://www.adafruit.com/product/306

Better post a picture of one section of your LED strip.
Leo..

Qdeathstar

#32
Jul 15, 2015, 01:54 am Last Edit: Jul 15, 2015, 01:55 am by Qdeathstar
Here is a picture of the IC
A creaking creeping shadow
stiff against the freezing fog
glares at a tickless watch.

Time has failed him -- all things shall pass.

Qdeathstar

#33
Jul 15, 2015, 01:56 am Last Edit: Jul 15, 2015, 02:03 am by Qdeathstar
HOWEVER,

What if I want to change later to APAs? DO I really have to design another pcb for those? They also require level shifting.  What happens you apply 5v to a 12v-5v regulator?

This seems like it would be easy...

http://www.adafruit.com/products/1787

A creaking creeping shadow
stiff against the freezing fog
glares at a tickless watch.

Time has failed him -- all things shall pass.

Wawa

Educated guess..
That strip shows a 510ohm resistor feeding a 5.1volt zener diode.
~5volt for the IC.

You could try this before you venture into level shifting:

If you run the first IC on 3.3volt, it should be happy with the Teensy data, and it might pass it on to the next IC. Or maybe run the first chip on ~4volt.

Tack a 3.9volt zener across the zener on the LED strip (measure the voltage !).
Leo..




Qdeathstar

#35
Jul 15, 2015, 02:37 am Last Edit: Jul 15, 2015, 02:37 am by Qdeathstar
Ok,

but will grumpy mike's idea not work? He was on today but didn't give me all his attention :D

Whats wrong with the 74ls14? 
A creaking creeping shadow
stiff against the freezing fog
glares at a tickless watch.

Time has failed him -- all things shall pass.

Wawa

#36
Jul 15, 2015, 02:51 am Last Edit: Jul 15, 2015, 03:01 am by Wawa
Nothing wrong with his idea.

Just seems silly to use an axe to crack an egg.

Why not use a 5volt Arduino.
it will run on the same 12volt as the strip.
And has a 5volt out for your RF receiver.
Leo..

Qdeathstar

I think I can understand the 74ls14 easier, plus, I don't want to run the strips at 5 volts.. im using these where the power runs will be around 100ft... I won't have to worry about voltage drop as much if i'm using 12v instead of 5v... plus its easier to find high-amperage 12v transformers.
A creaking creeping shadow
stiff against the freezing fog
glares at a tickless watch.

Time has failed him -- all things shall pass.

Wawa

I don't want to run the strips at 5 volts..
?? I did not say to run the strip on 5volt.
I said run the first IC only on a lower voltage by changing the zener.
It will still drive the 12volt LEDs.
Leo..

Qdeathstar

#39
Jul 15, 2015, 03:16 am Last Edit: Jul 15, 2015, 03:18 am by Qdeathstar
oh, I misunderstood...

I don't have a Zener.... next time I order something ill through a few in the cart...

can you tell me, is the 74ls14 hooked up correctly in my schematic?

And can the decoupling capacitors be hooked up to the ground plane on the negative side?

And do I need a heatsink on my power regulator?
A creaking creeping shadow
stiff against the freezing fog
glares at a tickless watch.

Time has failed him -- all things shall pass.

Wawa

#40
Jul 15, 2015, 03:20 am Last Edit: Jul 15, 2015, 04:16 am by Wawa
Improvise.
Two normal 1.8volt LEDs in series is a perfect 3.6volt zener.

Don't know if it's wise to use the LS family.
Last time I used one was in the eighties.
I use mostly HCTs now.
http://www.adafruit.com/products/1787
Runs on fumes, and is not inverting (no library tweaks).

Maybe make provisions on your board to use TWO strip outputs.
You have enough Teensy outputs and level translater ports...
Two the same patterns, or two different ones.

I don't think a TO220 7805 will need a heatsink.
I calculate, with the known parts, ~350mW.
Maybe better to use the 7111-5volt (smd) regulator, and use the ground plane as heatsink.
Leo..

Qdeathstar

I was looking at that chip earlier, but there doesn't appear to be eagle files for the chip...

I found 74Axxx125, and a couple of options under that.. but none of them are 74AHCT125.
A creaking creeping shadow
stiff against the freezing fog
glares at a tickless watch.

Time has failed him -- all things shall pass.

Wawa

#42
Jul 15, 2015, 04:34 am Last Edit: Jul 15, 2015, 05:08 am by Wawa
74xx-eu.lbr
74*125

Standard in the library.
Ignore the letters.
Leo..

Qdeathstar

I have edited the schematic with the newer chip..

A creaking creeping shadow
stiff against the freezing fog
glares at a tickless watch.

Time has failed him -- all things shall pass.

Wawa

#44
Jul 15, 2015, 06:50 am Last Edit: Jul 15, 2015, 07:13 am by Wawa
Unused Cmos inputs (NOT outputs) have to be grounded.
Search for *1117 in the parts.
You find a common/cheap 5volt SMD regulator
Leo..


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