Tag Archives: electronics sensors

Sensing Someone Around

This 3rd article in the series of “Do It Yourself: Electronics”, takes you through the basics of infra red sensing using an IR LED and an IR diode.

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Early morning, Pugs went to the ECE Department to meet Surya, who was creating some experiments for his juniors.

“What are you doing at this time in your department lab?”, exclaimed Pugs to Surya.

“Setting up a robot framework for our ECE juniors, for the robotic showcase planned for today afternoon”, replied Surya

“Interesting. I see that you are also using the IR transmitter and the IR receiver, you asked me to buy. By the name itself, I can make out that one would transmit IR signals, and other would receive the same. But what could we use them for?”

“These can be used for a wide range of applications …”

“To me it seems like another light sensor. Sun also emits IR. So, may be we can detect presence of sun”, interrupted Pugs.

“Why only sun? Even our bodies are good source of IR”, added Surya.

“Okay. So, do we detect sunlight, living beings, etc using the IR receiver? But then what is the IR transmitter for?”

“We can detect, but for that we may need more sophistication to eliminate the unwanted IRs. Anyways, the purpose here is not that. It is more of obstacle detection, and that’s where, we need this IR transmitter, as well.”

“I see. So, how do these IR Tx & Rx pair work?”

“Let me just show you a small working demo of the same.”

With that Surya picked up the various stuff needed, from around the lab, and showed the following:

Pugs went to his room & rebuilt the circuit. But to his surprise, the LED was always on. He tried debugging it, as in his previous light sensing circuit, but in vain. So, in frustration, he called up Surya and said, “Surya, your debugging gyaan is not working out. I tried all your suggested debugging tricks, but not able to figure out the problem in my circuit”.

“What happened? Have you powered up your circuit?”, queried Surya.

“Yes obviously. And that’s what the problem is. In my circuit, the LED is now always powered on”, replied Pugs with a sarcastic voice.

“Where have you put the circuit?”, asked Surya.

“On my table. Where else?”

“Put it below the table, and check out.”

“Why are you joking with me? How does it matter, whether I put it above or below the table?”

“Just try it, na”, emphasized Surya.

So, unwillingly Pugs put his circuit below the table, and viola the LED went off. And then, when he hovered his hand over the circuit, the LED switched on. He couldn’t believe himself. So, he tried the same multiple times. Then, he also put back the circuit on the table to check the problem, again. And yes, it was there. But all fine, when below the table.

“What happened Pugs? Did it work?”, asked Surya, as he didn’t receive any response from Pugs for a while.

“Yaaa. It is working. But how?”

“Now as it is working, I can explain you. Remember, you only told me that sun also emits IR, and your table is near the window. So, the IR receiver was always getting the IR, and hence LED was always on.”

“A ha! That’s cool. So, when I put it below the table – no IR from the sun – and things worked. That’s a great insight, that when we are playing with real world stuff, we need to keep our minds and thoughts open to all possibilities.”

“In fact, there is a simpler way to fix this problem. But I thought, why not have this fun experience.”

“What’s that?”, asked Pugs curiously.

“You may just adjust the pot to appropriately set the threshold value, depending on where you are keeping your circuit.”

“O ya! That’s what we have put the pot for.”

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Sensing the Light Around

This 2nd article in the series of “Do It Yourself: Electronics”, starts with the journey of sensors.

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After attending their regular afternoon classes, Surya & Pugs met near the Innovation Centre, headed towards their hostel rooms.

“What a waste of energy!”, exclaimed Surya pointing out to the street lights glowing on in the bright day.

“Possibly the switch man is not well and couldn’t come to switch off the lights”, said Pugs calming Surya.

“But, why do you need a switch man for switching on and off street lights?”, retorted Surya.

“What do you mean?”, asked Pugs with a puzzled look.

“These could be made automatic – what else?”

“Switch man may be more cost-effective than automating all these street lights.”

“I don’t think so – given that it can be achieved by simple & cheap electronic circuitry.”

“O Really! Then, why don’t we make and give it to the college? And, I can learn a new circuit.”

“Not a bad idea. Let us then first make a working sample.”

With that Pugs followed Surya into his room to watch the design evolve.

“By the way, what kind of circuit would it be?”, asked Pugs curiously.

“Think and you tell me. That is the first part of the design”, replied Surya.

Pugs contemplated a while and said “Something which switches off when sunlight is there.”

“Not bad. In fact, it should also switch on when light is less. And, that’s a light sensing circuit.”

“But how do we sense light electronically?”

“Why only light? A whole lot of stuff around us can be sensed using components called sensors. They come in whole variety, converting one form of energy into an another. And in electronics, we would like to use those that some how translates the energy into voltage. We have light sensors, sound sensors, humidity sensors, … – you name it.”

“Wow! So, then we can automate all kind of things.”

“Yes. That’s the power & beauty of sensors.”

With that, Surya takes out the light dependent resistor (LDR) and various other components needed for designing the light sensing circuit. And, here is how he demonstrated the complete design and working to Pugs:

As soon as Surya was done, Pugs quipped “That was simple. Even I can do it, now.”

“Exactly, that’s what I was telling you”, boosted Surya, dismantling the so built breadboard design.

“Hey, why are you breaking it?”, asked Pugs trying to stop Surya.

“That was simple. And so now you design it”, replied Surya challenging Pugs to redo the design on his own.

Pugs took up the challenge, and started building the circuit. He used the following two pointers from the notes taken by him during Surya’s demo:

LDR Circuit

LDR Circuit

741 OpAmp Pinout

741 OpAmp Pinout

He took some time but was able to build a similar circuit. However, to his surprise, it was not working. He tried tightening the ICs, shaking the wires – but no luck. Not wanting to give up his first circuit design challenge, he said “Hey Surya, I feel that circuit connections are okay, but something else is wrong. In programming, if we are not getting output, we can debug our program by putting prints. Is there something like that, I can do here as well?”

Surya gave a naughty smile understanding Pugs’ intention of not giving up, and poked “So, do you want me to debug it for you?”

“No-no. You just tell me the techniques of debugging. I’ll do it myself”, retorted Pugs.

“Okay then. Let me give you a quick debugging demo of possibilities” – and here’s what Surya showed to Pugs:

With that, Pugs was literally able to debug his circuit, and get the LED switch on when light is there and switch off when light is covered. “Aha! that’s not quite right. The logic is inverted”, exclaimed Pugs. At this, Surya couldn’t control himself, and quipped, “Yes. That’s because you have swapped the -ve and +ve connections of the Opamp.”

With that, Pugs reversed the connections and viola – everything was working right.

Super excited with the light sensing gyan from Surya, Pugs went to the local market to purchase the various components to build his own circuits. He purchased all the stuff shown to him by Surya till now, and then called up Surya asking what else shall he purchase, may be for his next circuit experiment. Surya suggested him to get an infra red transmit LED, an infra red receive diode, and four BC546 transistors.

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