enter image description hereenter image description hereI am using my CD4011BE NAND Gate IC. I connected a 9V battery in the 14th pin. And grounded the 7th pin. Then I provided input in the first 2 pins. I took a 330 ohm resistor from the third pin and connected an LED with that resistor and then grounded the other side of the LED.

I checked every possible configurations of the 2 inputs {(0,0),(0,1),(1,0),(1,1)}. But the outputs are not as expected. The LED never lights up.

I changed my IC and used another one of these CD4011BE and got surprised to see that this time the LED always lights up.

I am new to making circuits and electronics. So excuse my mistakes and please point them out.

  • \$\begingroup\$ Do you have pull-up resistors on the inputs? Or when you are giving it a '0' are you just leaving it? The issue could be to do with floating pins. Can you use the schematic editor to show us how you have set it up, and how you are providing a 1 or a 0 to the input? \$\endgroup\$ – MCG Aug 21 '19 at 15:13
  • \$\begingroup\$ When I am providing 0 I am grounding the input pin \$\endgroup\$ – Kabir Uddin Aug 21 '19 at 15:13
  • \$\begingroup\$ Try using pull-up resistors on the inputs, and a switch to ground it. Do this on both inputs so you can toggle them separately, then see what happens \$\endgroup\$ – MCG Aug 21 '19 at 15:16
  • \$\begingroup\$ I firstly used switches. When I found them not working, then to simplify- I used simply jumper wires \$\endgroup\$ – Kabir Uddin Aug 21 '19 at 15:17
  • \$\begingroup\$ Can you please draw a schematic and edit it into the question, along with a photo of the setup. That could be helpful \$\endgroup\$ – MCG Aug 21 '19 at 15:17

There are a number of possible problems you could have had here.

As the 4000 series logic chips are based on FETs, it's rather easy to fry them with static electricity when touching them (antistatic wristbands are nice to have).

Secondly, are you sure you connected to the pins you thought you did? Maybe you had the chip turned around, or maybe you were off by one position.

Or perhaps you even just got immensely unlucky and got a bad chip from the factory. It doesn't happen often, but chip fabs aren't infallible.

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  • \$\begingroup\$ I don't think so. This is exactly my first thought, but I re-read the last line to see that OP mentions the replacement IC had the LED always on, not that it was working, hence my asking for clarification on how the inputs are configured \$\endgroup\$ – MCG Aug 21 '19 at 15:15
  • \$\begingroup\$ @MCG Yeah, I reread that too and deleted the part where I suggested that they shouldn't worry because other ones are fine. It is still possible that they fried both chips with static; especially if these are old chips it's pretty easy to fry them inadvertently. \$\endgroup\$ – Hearth Aug 21 '19 at 15:16
  • \$\begingroup\$ I connected the pins correctly. \$\endgroup\$ – Kabir Uddin Aug 21 '19 at 15:17
  • \$\begingroup\$ The datasheet seem to indicate that the output current is only few mA, which is not going to work with the circuit OP described. Or I am reading some wrong data... \$\endgroup\$ – Eugene Sh. Aug 21 '19 at 15:17
  • \$\begingroup\$ @EugeneSh. A few mA is enough to light up an LED, even one of the older types, enough to be visible. Sure, you won't illuminate a room with it, but it'll show you the output state unless I'm quite mistaken. \$\endgroup\$ – Hearth Aug 21 '19 at 15:19

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