HOW TO CONSTRUCT A LED SEQUENCER USING CD4017

In my recent article I discuss how to use a Decade counter popularly known as CD4017 (Divide by 10) to switch a lamp or load. In this article, we shall look into how to still use a decade counter 4017 to drive series of L.E.D to form a circle, a pattern or a line etc pending on your desire.

Recall that a decade counter (also known as divide-by-10) has 10 outputs. These outputs can sink a current required to operate a L.E.D. But since we want the operation to be sequential i.e. coming on and off one after the other in ascending or descending pattern, we therefore would need another stage that will be generating a steady pulse or oscillation for us to clock the counter.

Knowing what we want, we will go for a clock generating Integrated Circuit. So far, the basic simplest bone is NE555 popularly known as a Timer I.C or Timer. In my coming article I shall discuss 555 Integrated Circuits in details.

NE555 is an 8 terminal I.C with RC (Resistor-Capacitor Network) frequency determining arrangement. The connection of 555 will determining its application as it can also be use as a Monostable Multivibrator (One-Shot Trigger). In this discussion, we shall be using it as a clock generator r oscillator to provide is a stable pulse to serve as our trigger to the counter independent of an operator manually triggering the unit to make a sequence display.

Following my connection as shown bellow, with the right component values, you will be able to construct a Timer and a counter to drive L.E.Ds.

Now, connect a fixed value resistor say 4.7k in between pin 7 and 8 of the 555 I.C.

Next, connect a 1k resistor in series with a variable resistor of 100k in between pin 7 and pin 6.

Next, connect a 10 uF capacitor in between pin 6 and pin 1 of the 555 I.C.

Next, link pin 2 of the 555 timer to pin 6 using a jumper or conductor.

Next, connect pin 4 and pin 8 of the 555 timer to your supply rail (Power supply line).

Next, connect pin 1 of the 555 timer to ground (0 V) and pin 5 of the timer should be connected with a

100nF

capacitor to ground (0v). You can check my article on Capacitors in Blog Archives for tutorials how to identify and know capacitors.

Next, your pin 3 is now your output. You should get oscillating pulse from here if you follow my instructions above.

Now, we need to fix the counter Unit. You could also check the Archives by the left pane of this site on how to use a decade counter as a switch for familiarity sake.

Now, just follow my connections as seen below, by connecting pin 8 and pin 13 of the counter 4017 to ground (0V).

Next, connect pin 16 to supply rail (power supply line). Connect pin 14 (clock input) to the pin 3 of the 555 timer. With this, you should have all your counters output jumping up and down sequentially. So, we just need to connect our LEDs to the outputs as shown below. Also, I shall give you more tutorials on LED soon ok!

Lets make it a date tomorrow as I hope to bring another information package your way again. You are special!

Isaac Johnson

Circuit Design And Technology

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How To Use A Decade Counter CD4017 To Switch-On Your Bulb

CD4017 is a decade counter

Popularly known as a Divide-by-10 counter. Yet, it can be reconnected to become a Divide-by-2 counter which directly is a Bistable Multivibrator. In using CD4017 Integrated Circuit as a switch, we must know the terminals and basic operations of a decade counter. 4017 is a decade counter that has 10 outputs with 1 input.

When the clock input is triggered by a clock pulse say a voltage (Low to High), its output jumps or advances to the next output. So, in every pulse received, the output advance to the next point until it gets to the 10th output and automatically reset back to the first output. Below is a schematic or diagram showing the pin configuration (connection):

The Pin 8 is connected to the ground, Pin 16 is connected to the Positive Supply rail (VCC) and Pin 15 is the Reset pin. Pin 13 is also connected to Ground (0V) and Pin 14 is the Clock Input to the I.C. The output of the counter are indicated with Pin Numbers 3, 2, 4, 7 and so on as show above in the diagram.

The input of the decade counter is pulled-down with a 470KΩ resistor to eliminate it been false triggered by stray signal or touching of the arms. The Rest pin is connected with an auto-reset network using a capacitor and a resistor to enable it return to its initial start point when the I.C is powered the first time. The 3rd output (Pin 4) is connected or fed back to the reset pin through a Diode to reset the outputs back to the start point when the output advances to the 3rd output. This is to say that, when the counter advances from point 1 to point 2, the next cock pulse will cause it to return back to the first point.

Next, we connect the output of the counter to a transistor. We did this because; the output from the counter is not sufficient enough to drive a relay that will close the contact of our Load. The transistor used in this case is a BC547 transistor used as a driver to energize a relay. We connected the 2nd output of the counter to bias the transistor (provide Base-Emitter voltage) for it to saturate (conduct). The biasing then causes electrons to migrate from the emitter to the collector of the transistor, thereby causing large drain of current from the collector to flow from the Power source (VCC), and through the Relay coil and the collector.

The contact of the relay coil now serves as our Open and Close Switch as it is in our houses. Here we then connect our Load, say an Electric Bulb or Socket of 230V AC from the source to the load with the contact been in series acting as the bridge or switch. Below is the detailed circuit diagram of the whole unit as explained above:

BC547 is not the only transistor that can be use in this case. Others include BC108, BC548, BC547, C1815, C9018, C9014 and lots more. Don’t forget also that aside using a decade counter to function as a switch, decade counters are also use in Frequency Divider, Sequence Display with L.E.Ds and lots more not listed here.

Please find time and check on my article tomorrow for other interesting tips I will disclose to you not discussed today.

Thanks, Isaac Johnson

Circuit Design and Technology

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