A very simple yet effective electronic toggle flip flop switch circuit can be built around the IC 4017.
By adding just a handful of other passive components the circuit can be made to toggle accurately through subsequent input triggers either manually or electronically.
A couple of very useful flip flop toggle switch circuits are explained here.
They may be operated through external triggers either manually or an electronic stage. Circuit schematics of these flip flop circuits have also been included.
Simple Electronic Toggle Switch Flip Flop Circuit Using IC 4017
We know that in response to every logic high pulse at pin #14, the output pins of the IC 4017 are switched high sequentially from # 3 to # 11 in the order: 3, 4, 2, 7, 1, 5, 6, 9, 10, and 11.
However, this proceeding may be stopped at any instant and repeated by just connecting any of the above pins to the reset pin # 15.
For example (in the present case), pin # 4 of the IC is connected to pin #15, therefore, sequence will be restricted and will bounce back to its initial position (pin # 3) each time the sequence (logic High) reaches pin # 4 and the cycle repeats.
It simply means that now the sequence toggles from pin # 3 to pin # 2 in a back and forth manner constituting a typical flip flop action. The operation of this electronic toggle switch circuit may be further understood as follows:
Every time a positive trigger is applied to the base of T1, it conducts and pulls down pin # 14 of the IC to ground. This brings the IC to a standby position.
The moment the trigger is removed, T1 stops conducting, pin # 14 now instantly receives a positive pulse from R1. The IC acknowledges this as a clock signal and quickly toggles its output from its initial pin #3 to pin #2.
The next pulse produces the same result so that now the output shifts from pin #2 to pin #4, but since pin #4 is connected to reset pin #15, as explained, the situation bounces back to pin #3 (initial point).
Thus the procedure is repeated every time T1 receives a trigger either manually or through an external circuit.
Accurate CMOS Flip Flop Circuit Using IC 4093
Another simple and very accurate flip flop circuit can be made using three gates of IC 4093. Looking at the figure we see that the inputs of N1 and N2 are joined together to form logic inverters, just like NOT gates.
It means that, any logic level applied to their inputs will be inverted at their outputs. Also, these two gates are connected in series to form a latch configuration with the help of a feedback loop via R5.
N1 and N2 will instantly latch the moment it senses a positive trigger at its input. Another gate N3 has been introduced basically to break this latch alternately after every subsequent input pulse.
The functioning of the circuit may be further understood with following explanation:
On receiving a pulse at the trigger input, N1 quickly responds, its output changes state forcing N2 to also change state.
This causes the output of N2 to go high providing a feedback (via R5) to N1’s input and both the gates latch in that position. At this position the output of N2 is locked at logic high, the preceding control circuit activates the relay and the connected load.
The high output also slowly charges C4, so that now one input of gate N3 becomes high. At this juncture, the other input of N3 is held at logic low by R7.
Now a pulse at the trigger point will make this input also go high momentarily, forcing its output to go low. This will pull the input of N1 to ground via D4, instantly breaking the latch.
This will make the output of N2 to go low, deactivating the transistor and the relay. The circuit is now back to its original state and ready for the next input trigger to repeat the entire procedure.
Parts List for FLIP FLOP CIRCUIT WITH IC 4017
R4 = 10K,
R5 = 100K,
R6, R7 = 4K7,
C6, C7 = 10µF/25V,
C8 = 1000µF/25V,
C10 = 0.1, DISC,
ALL DIODES ARE 1N4007,
IC = 4017,
T1 = BC 547, T2 = BC 557,
IC2 = 7812
TRANSFORMER = 0-12V, 500ma, INPUT AS PER AREA SPECIFICATIONS.
Parts List for FLIP FLOP CIRCUIT WITH IC 4093
R3 = 10K,
R4, R5 = 2M2,
R6, R7 = 39K,
R4, R5 = 0.22, DISC,
C6 = 100µF/25V,
D4, D5 = 1N4148,
T1 = BC 547,
IC = 4093,