NANDCat is an SAO compatible logic gate demonstrator/cute badge accessory.

The output (LED: D1) is a function of the inputs (Pushbuttons: SW1, SW2), here's the truth table for a NAND gate:

A (SW1) B (SW2) Y (D1)
0 0 1
1 0 1
0 1 1
1 1 0

The artwork is by @psd, who kindly let me turn it into a silly PCB. Thanks, Paul!


Bill of Materials

Designator Part Description
SW1, SW2 Omron B3S or similar 6mm SMD SPST-NO Tactile Switch
Q1, Q2 BC847B or similar NPN Transistor, SOT23 package
R1, R2, R4 1kΩ Generic 0603 resistor
R3, R5 100kΩ Generic 0603 resistor
D1 3mm LED Generic LED, diffused lenses are better
J1 2x3 100mil header Generic header
BAT1 Keystone 3034 or similar SMD 20mm coin cell holder

SW1 and SW2 use the ubiquitous 6mm SMD pushbutton footprint, the Omron part is for reference only and there should be many other, cheaper, parts that can be used there. Same goes for BAT1.

Q1 and Q2 can be pretty much any NPN transistor in SOT23 package that has the following pinout:

Transistor pinout

Go crazy with your LED choice and decorations!



  • Revision A (Oct 2019)
    • Initial release.
  • Revision B (Nov 2019)
    • Added a battery holder (CR2032) and some exposed copper for a brooch/pin back.


Ping @OmerK