Level shifter issues (1 reply)

Hey all,

Long story short, I'm working on a project connecting an LPCXpresso 1769 with my RAMPS, using some protoboard and a ton of wire. Since the LPCXpresso is a 3.3V board, I decided to use a level shifter to switch the MOSFETs. Unfortunately, it's not working.

I'm using this shifter, 3.3V on side A and 5V on B. If I switch the various pins on and off, on the A side (3.3V, connected to MCU) the voltage is correct. However, the B side acts bizarrely. If I don't have anything connected, and I'm just reading voltage, they will switch up to 5, but won't switch off until I disconnect the voltmeter and reconnect it. If I have the RAMPS connected, and switch one of them on, they all switch on, and none of them will switch off until I disconnect power. As far as I can tell, I have it wired properly, VCCA=3.3V, VCCB=5V, GND=GND, OE=VCCA, pins all to the appropriate ports, the RAMPS works fine on the Arduino, and I don't have any shorts between lines. At this point, I have no idea what to do. Are there resistors I'm supposed to add anywhere? Should I replace it with a unidirectional shifter? Did I totally fail to understand the purpose of the OE pin?

Any help is appreciated,
Chris