Re: Logic Level Converter
That is some fun wiring, but the connections do seem to match the circuit diagram. ;-) The next step is to make sure the connections are actually working. Breadboards are notorious for being wonky.
Do you have a multimeter with a connectivity/diode-test function? If so, touch the probes to the PCB pads at both ends of each wire and you should get a beep if there's a good connection. If not, you can use an ohmmeter and look for resistances of zero ohms (or some low value) between points that are supposed to be connected. Also check the voltages between the VCC and GND pins of both breakout boards, just to be sure power is getting where it's supposed to.
Next, do a basic sanity test on the level-shifting circuits. Disconnect the lead to the 3.3v input, connect the 5v input to GND, and measure the voltage at the 3.3v input pin. It should be GND or something close to it. Disconnect the lead to the 5v input, connect the 3.3v input to GND, and check the 5v side. It should be GND again.
If your multimeter has a frequency counter, get the clock running and check for the right frequency on the B2, A2, and CLK pads on the breakouts.
If all else fails, try tightening up your wiring. I2C clocks run at 100kHz and 400kHz, long looped wires have inductance, and breadboards have a lot of stray capacitance. It's possible that parasitic effects are messing with the signals.
Do solder all your header pins to the breadboards.. you might not notice the effects of a pin making and breaking contact for a few milliseconds, but trust me, the I2C circuits will.
To dig deeper than that you'll need more than just a multimeter.. an oscilloscope or logic analyzer would be ideal, but they're both pricey. If you have a second Arduino, you can fake a logic analyzer by sampling input pins really fast, but that's an adventure we can discuss if you end up needing it.
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