Home > Circuit Bricks > Logic Gate Bistable
UPDATED:.20:56 21 October 2013

FUNCTION BLOCK
DESCRIPTION
THIS USES LOGIC DEVICES
Logic 1 = High = +V
Logic 0 = Low = 0V

  • This bistable is built around 2 LOGIC gates.
  • This device can be set on or reset off
  • Useful to record events and start sequences.
CIRCUIT DETAILS
Input

NOR GATE BISTABLE - Circuit Diagram

Set
A
high pulse on this input will set the output (Q) on. This will overide a reset pulse.

Reset
A
high pulse on this input will reset the output (Q) off.

The pull-down resistors are ony needed if the inputs are connected to switches.

Output

The output (Q) can only sink/source about 2-3mA, just enough for an LED (but this will reduce the output voltage).

It should really only be used to trigger other logic devices - but you can add a driver for higher current.


Input

NAND GATE BISTABLE - Circuit Diagram

Set
A
low pulse on this input will set the output (Q) on.

Reset
A
low pulse on this input will reset the output (Q) off. This will overide a set pulse.

The pull-up resistors are ony needed if the inputs are connected to switches.

Output

Again the output is only 2-3mA and should be connected to another logic device.

PACKAGE DETAILS
Both the NOR and NAND gates come in a 14pin DIL package. Any gate can be used for any purpose. CMOS types have been chosen since their supply voltage can range from 3 to 15v.

4001B
2ip NOR GATE

4011B
2ip NAND GATE

When using ICs, it is always best to use an IC socket so the IC can be removed easily if needed.

Unused gates should have their inputs connected to 0v
Both the NOR and NAND bistables can be found ready assembled in another IC. There are 4 of them (equivalent to 8 gates) in a package - the details are as follows:

4043 = 4 x NOR gate Bistables
4044 = 4 x NAND gate Bistables

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