Do you know that the horizontal strips of a breadboard are all connected together (except sometimes in the middle)? To me this looks like you have shorted the input to the output of the 7805. (Or maybe the output to te ground, my view is blocked by the capacitor.)
![enter image description here](https://i.stack.imgur.com/tYkSU.jpg)
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OK, next step. You are using a plain old 7400, no LS or HC or any other letters between the 74 and 00? That old chip requires 5V. If you used it at 9V you can't assume it is still working correct. It might, but don't count on it.
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I can't make sense of your LED question. You don't mention a series resistor, did you use one?A LED nearly always requires a series resistor. For starters, take 1k.
If I understand your problem statement correctly, you are saying that when you try to transmit a logical low from at lest one device to the Due, the level converter only manages to pull the Due RX wire down to 2 Volts?
What does the RX wire look like on the other end (5V end) of the converter?
I would expect something like this to happen if the sensors are using too strong pull-ups, or if they are not intended for fan-in, and thus all try to transmit a logical high when one of them is trying to transmit a logical low.
If that's the problem, I would attach each of the sensors with a diode, Cathode towards the sensors, such that the sensors can only pull the line down, not up. Then I would use a pull-up on the common end (anodes) of the diodes, which you connect to the level translator input. Perhaps a 2.2 kOhm pull-up would be appropriate (giving about 2.5 mA current through the diode when pulled low.)
Also, did you read the top paragraph of the description you linked to? The part that says:
Sale: We've released a new rev of this Logic Level Converter that fixes the issue with the board not stepping down from 5V to 3.3V correctly. We've also dropped the price on this model and we will not be stocking this rev again once it's gone. Get it while you can!
Best Answer
74xx05 ICs have open collector outputs. Therefore, when the input is high, the output is pulled down, but when the input is low, the output is in high impedance.
To get an high level output, you should connect a pull-up resistor between the output and VCC (5V). Or, use the push-pull (totem pole) output version, i.e. 7404.
simulate this circuit – Schematic created using CircuitLab
The value of the pull-up resistor R1 mainly depends on:
In practice, what dominates is the first constraint.
The considerations above set the upper bound resistor value. The lower bound is determined by:
Typically unless you want to go at "high speed" (> 1 MHz) and unless you must connect this output to many inputs (high fanout), a classic \$10\ k\Omega\$ is enough.
Bonus fact
You can create a "wired-nor" gate, by connecting the outputs of two or more inverters of the 7405! Take a look at the circuit below: when A="1" OR B="1", the output is pulled low. When A="0" and B="0", then the output is pulled high by R1.
simulate this circuit
Don't do this with regular 7404 gates!
Notes: