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View Full Version : How do I get the Adafruit 8-channel bi-dierctional logic level converter to work



MichaelMeissner
01-10-2013, 03:53 AM
I'm probably missing something simple. Does anybody have a wiring diagram of how to set up the Adafruit 8-channel bi-directional Logic Level Converter - TXB0108? Here is the url for it: http://www.adafruit.com/products/395.

On the Teensy 3.0, I hooked the VCCB pin on the logic converter to the VIN pin on the Teensy, which gives me 5 volts. I hooked up the VCCA pin on the logic converter to the Teensy standard 3.3 voltage pin, and I hooked up the logic converter ground to Teensy's ground. I've tried connecting 5v power (from Teensy's VIN) to one of the B pins (say B3) and then connecting a LED or my volt meter to the corresponding A pin (A3), and from there to ground, on the theory that the logic converter should convert from 5v to 3.3v. I didn't get anything. Then I tried it the other way around, and connected a 3.3v line to say A4, and then I connected B4 to a LED and then ground, and again I didn't get anything. Now, I didn't connect the OE pin. Should I connect it to ground? Or maybe tie it to one of the power pins (VCCB or VCCA)?

PaulStoffregen
01-10-2013, 11:38 AM
Maybe it can't drive an LED? Some of those chips work by driving a strong signal only for several ns, just to rapidly change the voltage. Then they revert to a very weak drive to maintain the voltage. It's meant to work with inputs to chips, but not with heavy loads like an LED. Try using a voltmeter to view the output, or connect the output to a buffer chip that can drive the LED.

Constantin
01-11-2013, 01:05 AM
I'd check the datasheet on the TXB0108 (http://www.ti.com/product/txb0108). I agree with Paul that it probably cannot drive a LED. I have used these chips with great success for level shifting signals for the SD card on an 5V Arduino, for example. Or to drive the SIM900 chip from a 5V Arduino.