#062 SR Latch Flipper

Set/Reset latch with BJTs, controlled and monitored by an Arduino.

Here’s a quick video of the circuit in action:

Notes

This is a classic Set-Reset latch under Arduino control.

See the LEAP#061 SRLatch project for the implementation details and design notes on the flip-flop. SRLatch uses manual switch entry to control the flip-flop.

This version of the circuit uses an Arduino to drive the set/reset inputs, and monitor the output state. For simplicity, the circuit is powered from the Arduino’s 5V regulated pin. Output state is read with analog ports, and the data sent to the serial port for plotting with LEAP#090 PlotNValues (a simple Processing sketch).

The processing trace below demonstrates the behaviour using 4 traces. From bottom to top:

• Lower plot: SET input
• Lower-middle plot: RESET input
• Upper-middle: Out1 output state Q
• Upper plot: Out2 inverted output state -Q

The plot demonstrates:

• how repeated triggers have no effect on the output
• SET sends Out1/Q high
• RESET sends Out1/Q low
• Out2/-Q is always the inverse of Out1/Q

Construction

Credits and References

• LEAP#061 SRLatch - same project, but with manual inputs rather than Arduino control
• S9013 Datasheet
• SR latch - wikibooks
• Flip-flop - wikipedia
• PCB heaven - demo circuit used as the basis for this project
• ..as mentioned on my blog