Boosting Logic Voltage (LED Strips on Teensy)

I apologize ahead of time if we are only supposed to talk about Arduinos. But, the Teensy is super small and has more ram than the mega.

My issue is that I want to control LED strips using the teensy, but it seems the logic level outputs are only 3.3v which wont work, so I need a buffer to increase the voltage.

What do you recommend. Ideally, id like something easy to solder (through pin)

Also, I need 5v for the teensy and a 433mhz receiver from a 12v supply (the leds run on 12v) so could I use a voltage divider here? Thanks!

What do you recommend.

It depends on the current that the LED strip takes. If < 500mA use a transistor, a TIP120 or similar. If >500mA then use a logic level FET.

so could I use a voltage divider here?

No use a voltage regulator to drop the supply voltage. You can only use a divider to cut down signals.

Can use a low voltage level gate like this one http://www.digikey.com/product-search/en?pv959=13&pv69=80&FV=fff40015%2Cfff8007d&k=n-channel+mosfet&mnonly=0&newproducts=0&ColumnSort=0&page=1&stock=1&quantity=0&ptm=0&fid=0&pageSize=25 for the teensy to turn on to connect cathode of LED strip to GND to turn the LEDs on. LED strips are typically 3 LEDs in series with a current limit resistor, drawing about 20mA. So this MOSFET is good for ~ 15 LEDs worth of strip.

5V regulator to as GM says for the 12V to 5V supply.

I should have been more clear,

The leds are LPD8806's and have a clock and data line....

Ah, so addressable LED strips then, such as http://www.adafruit.com/product/306 3.3V to 5V adapter would be good - could be a simple 74HCxx gate, such as http://www.digikey.com/product-detail/en/SN74HC08N/296-1570-5-ND/277216

I have used a 74LS14 to step up from 3V3 to the 5V system. You need to use a 510R seriese resistor on the signal and a hefty capacitor on the output.

Seems a bit overkill Mike. How much current does the control line into a CMOS-based LDP8806 need? https://frack.nl/w/images/3/33/LPD8806_datasheet.pdf

Not sure what is overkill? The resistor is there to stop reflections on the line. The capacitor is for the led supply. You need two non inverted signals so a 74LS14 will provide six inverters but you only need four.

I was thinking running the Clock and Data lines thru 2 gates to get them from 3.3V out of the Teensy to 5V into the first LPD8806 on the LED strip. Not sure reflections would be a big problem there if the strip is connected with decent wiring to whatever the 3.3 to 5V buffer is. Couldn't hurt I suppose. I could see a cap on the supply line if the LED strip didn't have that already.

Thanks for your comments guys.

After reading the comments, it seems like the 74LS14 is the "best" option

I was trying to get this set up in eagle, and I think I found the chip, but when I add it to my schematic, it only adds a pair of "pins" at a time... but the vcc and gnd pin don't show up?

Also, VCC in this case would be 5v correct? And I'm taking the signal from the eagle, to an input pin on the 74LS14, then taking the output and putting it back to another input pin? To invert the signal twice so it becomes "uninverted"?

Lastly, the datasheet http://www.futurlec.com/74LS/74LS14.shtml is limited... how do you know where the capacitor and resistors need to be, and the correct value?

Untitled.png|1920x1080

Just a question about level shifters from 3.3 to 5v. Would a 74LS14 really be much better than a pullup resistor to 5v, and a diode from the 3.3v output, allowing the output to only pull the signal low?

In Eagle, right click and select Invoke to grab the power pins.

Diode with pullup - that won't keep 5V off the 3.3V output pins.

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

Try a 2N7000. Gate to teensy port, source to ground, drain to LED data pin. No other parts.

Leo..

How would that boost the logic voltage?

The pull-up resistors inside the first LED driver IC should pull-up the data/clock lines to it's own 5volt supply. The mosfet just pulls that pin to ground when data is flowing.

Data/clock goes only to the first IC in the LED string. The first chip passes things on to the next one.

NO long lines between teensy and LED strip.... Too much wiring capacitance, and data will be corrupted.

You could try a transistor (and 1k base resistor) if you haven't got a small mosfet. But transistors could get saturated, and have slow switching speeds. A schottky diode across B/C (baker clamp) could help. Leo..

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

No.

Qdeathstar: How would that boost the logic voltage?

You would need a pull up resistor on the drain. The signal would then be inverted.

Well. A lot to consider.

I worked on a schematic based on what we had talked about with the 74LC14... I think I have it right, but i'm not sure about the resistor values or capacitor values, what type of capacitor, ect....

I tried looking at this... but it is a different chip..

http://www.adafruit.com/product/1779

It looks like a ceramic capacitor and from what I can read, 100ohm resistors... why 100 ohm?

Here is the schematic I have so far:

Untitled.png|2083x1000

The 74HCT245 is an octal non inverting buffer, so you would only need two out of the eight buffers in the chip. It can also be a switched bi directional buffer but you don't need that. It is a more modern chip but otherwise offers no particular advantage.

Connect the unused inputs of the 74LS14 to ground for stability.

It looks like a ceramic capacitor

What does? It is normal to use a ceramic capacitor for decoupling and you should put one across the power pins of the 74LS14.

why 100 ohm

It is not too critical. It is there to soak up reflected signals and damp down any standing wave that could build up. Those two things are actually the same thing.

Grumpy_Mike: The 74HCT245 is an octal non inverting buffer, so you would only need two out of the eight buffers in the chip. It can also be a switched bi directional buffer but you don't need that. It is a more modern chip but otherwise offers no particular advantage.

Connect the unused inputs of the 74LS14 to ground for stability.

Ok

What does? It is normal to use a ceramic capacitor for decoupling and you should put one across the power pins of the 74LS14.

In the picture of the octoWS2811 I was using as a reference, there is a ceramic capacitor there tooo, I just wanted to make sure I should a ceramic one. Should I use a 100uf capacitor?

Should I use a 100uf capacitor?

Well you can't buy a 100uF ceramic capacitor. It needs to be 0.1uF or 100nF ( they are the same thing )