Running led reduced transistors

circuit diagram-

About Every circuit:-

this circuit was made using "every circuit" . Every Circuit is a circuit simulation app which aids in making and testing simple circuits prior to be made on breadboard.You can watch the simulation in below given link.Open it in chrome or download app from play store its free in case it doesn't open on your smartphone or PC.

In the simulation I have used manual switching instead of transistor as switch.

http://everycircuit.com/circuit/5216980636532736/rolling-led

Circuit description:-

This is another running led circuit made by transistors. In this the concept of RC time constant is the same as the prior circuit. You can see the base resistor is in increasing by 50 ohm for each transistor from left to right.Here also we have used IC555 to generate square wave signal which is given to all transistor switching blocks. The square wave gives a discharge time for all capacitors for a fix period given by its "off time".

In this circuit we have reduced transistors .Instead of a transistor latch circuit (consisting of one NPN and PNP transistor) to turn on the output , we have just used a single PNP transistor BC557 to turn on the output.

This cricuit is only for those who are only concerned with the running effect of led and don't want a precise digital output ,as single transistor reduces precision but does performs same function of turning on the output once the base current is sufficient to take it into saturation.

you can add more blocks of transistor switches if you want more running led's. The only thing to remember is to take base resistor values in increasing order of 50ohm,100ohm depending on the time interval you want between two successive led's.

components used:- transistor BC557 & BC547, Timer IC555,capacitors 2.2uf,resistors,9V power supply or battery.

watch circuit demonstration in below video.