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I am using a 74F283PC 4 bit adder, and I am not sure why, but the LEDs are not working, like they will not change at all. I have no idea why it's not working, and I could use any help. The Schematic for the circuit I was using

This is the schematic, its connected to 5V and there are 1k resistors at every input, and LEDs to every output except carry out, which is connected straight to ground. When I change an input, the output does not change. Thank you in advance

Datasheet : http://eelinux.ee.usm.maine.edu/courses/ele172/docs/74F283.pdf

Danny Ryan
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    Suggestion: The components in the schematic are clogged, it's difficult to read. I strongly recommend you to redraw your schematic to add some spacing between your components. If you help other people to read your schematic better, ultimately, you'll have a better chance to get a good answer from others. You can use [Rules and guidelines for drawing good schematics](https://electronics.stackexchange.com/questions/28251/rules-and-guidelines-for-drawing-good-schematics/28255) as a reference. – 比尔盖子 Feb 28 '20 at 04:28
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    Why do you connect output (C4) to the ground? Which input do you "change" in hope do see the change in result? Please clarify what exactly you do, what you get, and what you expect to get. – Anonymous Feb 28 '20 at 06:55
  • What color are the LEDs? – Bruce Abbott Feb 28 '20 at 07:11
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    The outputs of any IC MUST NOT be connected directly to Ground or to Vcc. – Peter Bennett Feb 28 '20 at 07:42
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    The F283 will sink some decent current. But they won't source much. If you reverse the LED orientation and add series resistors to limit their current somewhat, I think you'll be better off. – jonk Feb 28 '20 at 07:46
  • That's not how you connect LEDs to a TTL device. –  Feb 28 '20 at 12:05

2 Answers2

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Reconfigure all the 1K resistors as pull-ups: connect them to V+ instead of ground. Now when you jumper an input to ground you will create a valid low. The LEDs should also be wired as pull-ups but with a resistor in series; 1K will be OK.

EinarA
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You must sink at least 1.2 mA from an input, and pull that input below 0.8 volts, fo rthe input to be seen as a logic Low, which means that your pull-down resistors must be less than 650 Ohms. With 1K pull-downs, the inputs are not guaranteed to be seen as a Low.

Peter Bennett
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