555-Timer as a Bistable Latch proteus simulation Schematic Circuit Diagram
Bistable Switches: Efficient Electric Load Controllers
Latching relays or bistable switches are versatile devices with two stable states, allowing them to effectively switch various electric loads. When in the switch-on position, these switches operate without any power consumption and have minimal consumption per pole.
Understanding Bistable States
The term “bistable” refers to the ability of a device to exist in either of two stable states. A classic example is a mechanical light switch, which can rest in the “on” or “off” position but not in between these states.
Utilizing RS Latch in 555 Timer
The RS latch in the 555 Timer can be harnessed using the Reset and Trigger inputs. Momentary inputs applied at these points set or reset the output. The S and R inputs are influenced by Op-Amp outputs, controlled by trigger and threshold inputs. When the switches are in the normally open state, the Op-Amp outputs maintain R, S inputs at 0,0 (LOW state), allowing the RS Latch output to retain its previous state.
Bistable Latch using 555
Bi-Stable Latch Using 555 Timer’s Trigger and Threshold Inputs
In the circuit above, the Bi-Stable latch utilizes the Trigger and Threshold inputs of the 555 Timer. The Upper Comparator (UC) output acts as the Reset input for the RS Latch. It goes High when the Threshold input is greater than 2/3 Vcc, causing it to be Pulled Down. In this state, with a high Reset input and a low Set input, the output is Reset, i.e., Low.
The Lower Comparator (LC) output serves as the Set input for the RS Latch. It goes High when the Trigger input is less than 1/3 Vcc, pulling it High. When the Set input is high and the Reset input is low, the output is set, i.e., High.
Bistable Latch using 555
The above circuit is a Bi-Stable latch using Trigger and Reset inputs of 555 Timer. The Threshold input is left open or can be Pulled Down. Irrespective of the Trigger input, When the Reset input is Low, the output is Reset i.e., Low, and so Reset pin is Pulled Up. The output of LC(Lower Comparator) which is the Set input to RS Latch is High when the Trigger input is Low or Lesser than 1/3 Vcc, so it is Pulled Up.
