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I have recently bought this IC:

enter image description here

It's a NAND gate. So just to be clear, we agree that if both inputs are 1, the output will be 0. (The IC is a Quad 2-input NAND-gate 74HCT03, the datasheet can be found here )

This chip just won't work for me. I'm using a breadboard as you can see beolow, and no matter what I do, it wont work.

enter image description here

As you can see in the picture, I have connected the right side of the chip to +, and the left side to negative. This should mean that the IC is ON. I then connect the wires to pin 1 and 2. And a LED to pin 3. I have connected the pins to 10k resistors to ground, so they can be 0 if no power is on. I have tried to remove the switches and just create a wire that goes directly from + to pin 1 and 2 but nothing happens. The funny thing is that whenever I disconnect the wire that goes from pin 7 to ground, the LED starts to light. I migth be stupid, but I can't really figure this out..

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2 Answers 2

This is what the internal circuit looks like on the 74HC03 (from the datasheet).

enter image description here

To drive an LED, you need to do something like this: (left hand schematic, where gate and MOSFET are inside the chip). The right hand schematic shows a pullup resistor (again the gate and MOSFET are inside the chip).

schematic

simulate this circuit – Schematic created using CircuitLab

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The 74HCT03 has open-drain outputs. You will need to add a pull-up resistor to see the output go high.

Also, please give us a proper schematic. The poor photo of your breadboard is not very helpful.

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Thanks for you answer, and i do know that the picture is silly, i just dunno how to make schematic. You say pullup resistor, do i have to connect it from pin 14 or? .. –  Emil Møller Ringgaard Apr 9 at 18:18
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The pullup resistor goes from the NAND gate output pin to the power supply voltage. The NAND gates in this chip can only pull the output low, so you need something else to pull the output high (assuming that you want to see it go high). –  Joe Hass Apr 9 at 18:20

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