Suppose it is a rainy night. The weather was warm at bedtime. You kept fan on. Suddenly at mid-night weather becomes cold. Then you have to turn off the fan. Then you have to get out of bed, if there is no bed-switch facility.
Now what about the system of switching off the fan from bed?
Today I’ve made a very simple circuit for you. This is not new but useful.
A Decade counter IC is used to control the whole process. And the other main part is an IR Receiver. We will discuss the circuit diagram later. First, we will take a look on the IC.
The CD4017 is a CMOS decade counter IC. Basically, it is used in small range counting applications. It can count from 0 to 9 (decade count). Moreover, its operating voltage range is large enough. It can be operated from 3V to 15V which is enough to run this IC from a Li-ion Battery. Pin 16 is for positive supply voltage and pin 8 is for Ground. Pin 13 is Enable pin. The IC will be enabled when this pin is connected to ground. You can learn more about this from here.
Now let’s take a look on the circuit diagram.
The whole circuit has three part, 1) Signal input, 2) Counting part, 3) Output part.
1. Signal input part:
This part consists of an IR receiver (TSOP1738), some resistor, capacitor and a PNP Transistor (BC557). Output of the TSOP1738 goes to the base pin of the transistor through a 10K resistor. The output pin is grounded by a 1uF capacitor. When the TSOP detects the IR signal, it pulls its output LOW. This is done with low impedance, so discharges the capacitor quickly. When it stops pulling LOW, the capacitor gets charge up again thru 10K resistor and the internal pull up in the TSOP. In this way a LOW pulse goes to the base pin of a PNP transistor viz., BC557. Collector pin is connected to the 5V and emitter pin is grounded by 100K resistor. When the base pin becomes
LOW, the emitter pin becomes HIGH. And thus, this part makes a HIGH pulse for the IC CD4017.
2. Main Counting Part:
The HIGH pulse of previous part goes to the pin 14 (clock pin) of the IC. We know that when the IC gets a HIGH pulse, it changes its output from one pin to next pin. Output of this IC is HIGH. CD4017 has a feature of RESET. If we give a HIGH pulse on the pin 15 (RESET pin), the output state will reset. We have used this facility of the IC.
The output is taken from pin 2 (which is second output of the IC). Pin 4 (which is third output) is directly connected to pin 15 (RESET pin)
Thus, we have made the counting part.
3. Output part:
This is the last step of our project. The HIGH output goes to the base pin of an NPN transistor BC547 through a 1K resistor. We take the final output from its collector pin and its emitter pin is connected to ground.
Now we have taken a 12V relay. And 12V DC is supplied to one of the coil pins of the relay.
Another coil pin is connected to the collector pin of BC547.
When base pin gets HIGH pulse, its collector pin becomes LOW i.e. acts as ground. So, the relay becomes ON state. Again, when the base pin becomes LOW, the transistor stops to conduct and relay goes to OFF state.
A simple p-n junction diode 1N4007 is used to prevent the short-circuit of the two coil pins. Other 3 Relay pins are connected to a PCB terminal block to connect or disconnect AC Mains wire easily.
Now, let’s take a look on how relay turns ON —
An IR signal is given – TSOP1738 detects it – pulls its output LOW and send to the transistor BC557 – BC557 gives HIGH pulse – This pulse is sent to CD4017 IC – It makes the pin 2 HIGH and send this to the transistor BC547 – collector pin of BC547 becomes LOW – Relay becomes ON.
Well, let’s see how the relay becomes OFF —
Again an IR signal is given – TSOP1738 detects it – pulls its output LOW and send to the transistor BC557 – BC557 gives HIGH pulse – This pulse is sent to CD4017 IC
– Now the IC makes the pin 2 LOW and the pin 4 HIGH, since pin 4 is the next output of pin 2 – Whenever pin 4 is HIGH, it send this HIGH pulse to pin 15 and the IC is reset – Since pin 2 is LOW, it makes the transistor OFF – Consequently the relay becomes OFF.
Here in the schematic, a voltage regulator IC L7805 is used to convert 12V into 5V. The relay is of 12V where TSOP1738 is of 5V only. Here the IC is also operated by 5V. If you use 5V relay, then L7805 is useless here. Direct 5V supply voltage can do the whole process.
Thus, a remote-control switch can be made easily. Here the image that we made on Dot PCB at home.
To download PCB, click here.
Department of Mathematics
Burdwan Raj College, Burdwan
About the author: Diptangshu is now pursuing B.Sc in Mathematics with Electronics as Generic Paper from Burdwan Raj College,West Bengal. Along with Photography he is interested in participating in exhibition related to electronics and computer science.He loves to sing and his hobby is listening music.About this blog he says “The entire circuit design and PCB design is made by me. The circuit diagram is not new. It exists previously. I just represented and elaborated easily to our readers.Figure 3 claims that I did the whole thing myself.”