Sequential Timer Circuit Using NE555

This is a simple sequential timer circuit using NE555 which can be used for psychedelic light, decoration in shops, advertisement boards at night, and in parties. The circuit is similar to those published earlier, except for the fact that it incorporates some additional features.

Circuit Description Sequential Timer Using NE555

In the circuit sequential timer  circuit IC2, IC3 and IC4 are used as monostable multivibrators. The trigger terminals (pins 2) of these ICs are connected in chain to the previous ICs through RC differentiator network (0.022 µF capacitor and 22 KΩ resistor). IC1 is used as an astable multivibrator with adjustable duty cycle and time period.

To understand the functioning of the sequential timer  circuit, supposed the circuit is put in ‘all rotate’ position and lamp L1 is on. When lamp L1 goes to off state, as pin 3 of IC2 goes to the low state, it triggers IC3 through C9 and R9 differentiator, and thus lamp L2 switches on. In the next period, lamp L2 while going off switches on lamp L3 and so on, thus completing the chain.

sequential timer using ne555

When the switch SW1 is in ‘all on’ state, trigger terminal of each IC2, IC3 and IC4 is clamped to the ground and thus output of each goes high, making each of the lamp L1, L2 and L3 to switch on. This state is useful in checking for the fused lamps.

Since IC1 is put as astable multivibrator, when switch SW1is put to alternate position, for some time the lamps rotate and then for some time all of them glow simultaneously. For the given component values, the time period can be increased to about four seconds. This time period can be adjusted by VR1.

The effect on ‘alternate’ position comes from the facts that in this case trigger terminals of IC2, IC3 and IC4 are put to ‘all on’ and ‘all rotate’ positions automatically alternately, because output of IC1 goes to Vcc and ground level alternately.

Adjustment of the unit is simple. Put SW1 to all rotate position and adjust VR2, VR3 and VR4 so that each lamp glows for equal time, or the effect is most eye appeasing. Then put the switch to alternate position and adjust VR1 for most pleasing effect.

If many small lamps are to be used, a suitable sequence for connection of the lamps can be L1 L2 L3 L1 L2 L3—–.

Since the monistable IC2, IC3 and IC4 require an initial trigger to being cycling, the circuit may not operates if switch SW1 is in ‘all rotate’ position initially. In this case, switch SW1 to the ‘all on’ or ‘alternate’ position momentarily before switching back to the ‘all rotate’ position.

PARTS LIST OF SWQUENTIAL TIMER USING NE555

Resistor (all ¼-watt, ± 5% Carbon)

R1 = 200 KΩ

R2, R4, R6 = 1 KΩ

R3, R5, R7 = 10 KΩ

VR1 = 500 KΩ

VR2 – VR4 = 100 KΩ

Capacitors

C1 = 10 µF/12V

C2 – C4 = 2 µF/12V

C5 – C8 = 0.01 µF

C9 – C11 = 0.022 µF

Semiconductors

IC1 – IC4 = NE555

T1 – T3 = OT104 (400V, 1A)

Miscellaneous

L1 – L3 = max 150W lamps

SW1 = Rotary switch