First of all I am new to this whole circuit building thing so please don't be too harsh on me.

I recently tried to build my first adder with NAND gates. So I went to a shop and bought some CD74HCT03E devices. To get started I just tried out the NAND gate but it didn't work.

I had a really really basic setup: a NAND gate, the power supply, and a LED. I already verified this circuit with my physics teacher and he sad that everything is fine. I also checked every pin with my voltmeter. Every input (A/B grounded) were at 0V and the output (Y) flicker but were also at 0V.

Here is an image of my circuit: IMAGE

  • We can help you better if you include the schematic of what you're buidling. Scan a drawing or better: use the schematic drawing tool (Edit your question, press the schematic icon). – Bimpelrekkie May 31 '17 at 14:44
up vote 4 down vote accepted

74HCT03 is open drain output. That means it can only pull the output low.

Try it this way..

schematic

simulate this circuit – Schematic created using CircuitLab

  • Thank you really much, that schematic really helped me :) – Nimmi May 31 '17 at 15:09

The banner line title of the CD74HCT03E is

High-Speed CMOS Logic

Quad 2-Input NAND Gate with Open Drain

You got really unlucky on your first purchase, the NAND gate you purchased only drives low, it never drives high. It is an open-drain output.

You will need to add a pull-up resistor on 1Y to VCC.

You can also connect the LED directly to 1Y and move your ballast resistor as the pull-up to Vcc.

  • Thank you really much for you answer, it is working now :) – Nimmi May 31 '17 at 15:09
  • @Nimmi The part which you probably meant to buy is the 74(HCT)00, which has a "normal" (push-pull) output. – duskwuff May 31 '17 at 22:37

Try this circuit. It's how it should be connected.

Two 1's light LED.

schematic

simulate this circuit – Schematic created using CircuitLab

Open Drain (collector) have their applications, but it may be best to stay away from them when experimenting. Each output will require a "pull-up" to work.

One application is paralleling gates to a "wired OR" (or "wired AND") in this case. Otherwise a third gate is required.

In the following circuit, activate either NAND to turn on LED.

schematic

simulate this circuit

  • YUp this will work too.. though inverted – Trevor_G May 31 '17 at 15:13
  • @Trevor But that is how it is meant to be used. 8) – StainlessSteelRat May 31 '17 at 15:16
  • I'd say so..yes ;) – Trevor_G May 31 '17 at 15:22

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