I am attempting to build an XOR gate with NAND ICs. This schematic

is how I am wiring up the IC (I know the schematic is a little confusing but I tried to construct it best I can).

I am attempting to recreate this logic circuit: http://i42.tinypic.com/n4weo6.jpg

Data sheet for CD4011B IC: http://www.ti.com/lit/ds/symlink/cd4011b.pdf

It is not operating as expected, the LED is always on when I expect it to be off by default, off when both switches are pressed and only on when one or the other switch is pressed.

Have I wired this circuit incorrectly? Can anybody tell me where I have gone wrong?

enter image description here

  • \$\begingroup\$ A proper schematic with gates would be much easier to follow. \$\endgroup\$ Commented Jul 5, 2013 at 18:25
  • \$\begingroup\$ The link is not accessble: 'remote linking not available' \$\endgroup\$ Commented Jul 5, 2013 at 18:33
  • \$\begingroup\$ Sorry, please see image here: i42.tinypic.com/n4weo6.jpg \$\endgroup\$ Commented Jul 5, 2013 at 18:35
  • \$\begingroup\$ Provide a real schematic. -1 and voting to close in the mean time. \$\endgroup\$ Commented Jul 5, 2013 at 18:44
  • 1
    \$\begingroup\$ Would benefit from a current limiting resistor 470 ohm to the LED. \$\endgroup\$
    – pjc50
    Commented Jul 5, 2013 at 19:20

1 Answer 1


The circuit looks fine

The XOR table should be

                          A     B          Q
                          0     0          0         
                          0     1          1 
                          1     0          1 
                          1     1          0
  • \$\begingroup\$ Strange as the LED is always on! Thanks so much for your reply though, it may be a faulty IC. \$\endgroup\$ Commented Jul 5, 2013 at 18:59
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    \$\begingroup\$ @JacobClark Make yourself a simple logic probe to test around the circuit - 470R resistor with LED in series (or use a voltmeter). Connect the LED cathode to ground and test the pins of the IC. Start with the first gate and see if the output (pin 3) changes when you operate the switches. Make a note of the truth table. Then try pin 11 and then pin 10. Work your way through the circuit and follow the signal. It may simply be a bad connection somewhere. \$\endgroup\$ Commented Jul 5, 2013 at 19:12

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