# Boosting Logic Voltage (LED Strips on Teensy)

Can the decoupling capacitors be connected to the ground plane? I can't see a way to route them like this:

https://cdn.sparkfun.com/assets/2/6/7/7/e/51965e31ce395f412a000000.png

(just an example)

I can route the power, but the grounds just connect to my ground plane... Is that oK?

Wawa:
It seems that these chips have internal pull-up resistors.

Grumpy_Mike:
No.

Why would I say that without reading the datasheet first…

Leo…

I am using a 1.5amp voltage regulator to step down from 12v to 5v… I think that my current draw is at most around 100ma (35ma for the teensy, 6ma for the Heterdyne 433mhz rx, and I think I read a max of 20ma for the 74ls14? (Icch?). So that adds up to 61ma, so 100ma should be plently…

On adafruit, it says that the voltage regulator can drop 2w without a heat sink. I found this formula for wattage drop:

(InputVoltage - 5V) * AverageCurrentInAmps (12 - 5) * . 1 = .7

So I shouldn’t need a heat sink.

Please take a look at my schematic and let me know what you think…

TeensyRX.zip (51.6 KB)

I'm lost. Why termination resistors. What is the clock speed. Are you planning to go twice around the block with Cat-5. Will there also be 150ohm termination resistors at the end of the cable. And an amplifier, because your signal would have dropped to 2volt. Are you planning to drive one strip, multiple strips, series, in a star. ?? Leo..

Wawa:
I’m lost.
Why termination resistors. What is the clock speed.
Are you planning to go twice around the block with Cat-5.
Will there also be 150ohm termination resistors at the end of the cable.
And an amplifier, because your signal would have dropped to 2volt.
Are you planning to drive one strip, multiple strips, series, in a star.
??
Leo…

uhh…, this is the third board I have designed and the first two where just moving Arduino pins around… I only know what I interpreted from Google searches and these forums…

I’m not sure what you mean by termination resistors, but I assume you mean the ones for data and clock. I thought grump said I needd the for the 74s14. Clock speed, I don’t know… I think I read that lpd806 is 400hz, but I won’t be updating them more than 10 times a second…

I plan to have <1ft leads between the screw termina and the strip.

should there be 150 ohm termination resistors at the end of the strip? Im not sure, but I don’t think I need an amp… I think the 6808chips boost the signal… in testing I was able to connect three 5 meter strips together no problem straight from an arduino…

I was hoping to connect 6~8 strips together in series… around 40 meters max

Termination resistors are used when cable reflections are expected. High switch frequencies and long cables.

If your teensy is 30cm away from the first IC, there is no need for that.

And the LED chips are not boosting the signal, they are buffering the signal. You only drive the first IC. That IC buffers the data, and passes it on to the next one.

Try two small mosfets or two NPN transistors with 1k base resistors. Takes 10 minutes to hook that up on a breadboard. Make sure you reverse your output pin code. Leo..

Are you using the mosfets instead of the 74ls14 to get from 3.3v to 5v or in addition to it?

Connect a 5volt supply to the LED strip. Nothing else. Measure the clock and data voltages in respect to LED strip ground. You might find 5volt on the pins, because the LED IC is already pulling those pins up to it's own supply.

If so, all you have to do is switch those lines to ground, with a transistor.

Mesure that first, and report back. Leo..

The strips I'm using are 12v.

I measured from ground to data in and ground to clock in with just the 12v power supply connected and got 0 volts dc.

I verified 12v between ground and positive.

So you're NOT using the LED strips with the LPD8806 drive chip, mentioned in previous posts.

That chip has a maximum rating of 5.5volt, and would blow up on 12 volts.

??

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.

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

Here is a picture of the IC

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...

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..

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?

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..

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.

Qdeathstar: 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..

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?