Problems using a logic level shifter

I’m having some issues getting my logic level shifter from NKC to work properly, and I’m not sure I really understand why it’s working the way it is. I have this one http://store.nkcelectronics.com/5v-to-33v-logic-level-shifter-bo.html

I’m just blinking an LED, but I’m getting weird dimming issues when it shifts voltages. It almost looks like it’s not getting all the power running after it converts down to 3.3v and sometimes it looks like it’s not turning all the way off. It’s running on the standard Blink example in Arduino and using pin 12 to power the board. Setup is as follows:

12 (HIGH) → DIR
13 → A0
B0 → 10k resistor → LED → GND
GND → GND

Any ideas?

First question, what does a logic level shifter have to do with using a LED?

Why not just drive it directly?

Also, 10k is WAY too large for a LED current limit, I still don't get the converter thing but if you have 3v3 driving a LED then 100R would be closer to the mark.

Another also, that schematic doesn't show what voltages are connected to what. The '245 will need a 3v3 power supply from somewhere, or is that what the VCC is?


Rob

I'm just using the LED for testing out the board just to make sure it's working. I had it lying around but remembered not being able to use it with an Arduino Pro (5v) project I worked on last year. The goal is to use this with that same (now unused) Arduino Pro 5v, but if I have to also power it with a 3.3v that won't really help anything...

If I'm understanding correctly, what you're saying is that I also need to power the board with a 3.3v supply? Right now I'm just powering it using the 12 pin from my Uno to the DIR input on the board.

I know that the resistor is way too big, I also tested it out with a much smaller one, but still had the same problem.

Thanks for the help, Jeff

Yes you need to power that board with 3v3 before it will work.

So there's no way it can work with the 5v Arduino Pro?

http://www.fairchildsemi.com/pf/74/74LCX245.html

The LCX245 contains eight non-inverting bidirectional buffers with 3-STATE outputs and is intended for bus oriented applications. The device is designed for low voltage (2.5V and 3.3V) VCC applications with capability of interfacing to a 5V signal environment. The T/R# input determines the direction of data flow through the device. The OE# input disables both the A and B ports by placing them in a high impedance state.

http://www.fairchildsemi.com/ds/74/74LCX245.pdf

Looks like the NKC Electronics design uses a resistor to drop the 5V down some for Vcc. If you have 3.3V available use that instead.