Introduction: A Smart Wristband for Personal Air Conditioning and Heating

About: Hi. I am Abtahee from Bangladesh. I am a student of 11 th grade. I am interested in programming and robotics. But my main concern is researching about renewable energy source.Apart from that I love gaming and …

In this instructable,I will show you how to make a amazing wristband which looks like a bracelet but works like air conditioner or heater.

The purpose of this instructable is to make such a wearable which seems to be a normal wristband but can change your thermal feeling and replace air conditioning or room heating . It is actually a thermal environment simulator which makes you feel cooler in summer and warms you in winter when you put it in your hand.

In brief, It is a smart wristband which keeps you thermally comfortable in rough weather.

It is a cheap and affordable gadget which can replace room heater and air conditioner for it’s low cost , low power consumption and it’s portability.

So you don't have to pay for your air conditioner every month after making it. Just put it on your hand and roam anywhere in any kind of weather.

Best of Luck!

[This project has entered in the microcontroller contest. If you like it,please vote me. Being a winner will inspire me to write more instructables like this one.]

Step 1: Get the Necessary Things


1. Arduino Uno( You can also use nano. In fact,Arduino Nano would be a better option than uno for it's small size.)

2. L298N/L293D Motor Driver Module.(Each pin on an Arduino can handle 40 milli amperes. So directly connecting the peltier to arduino pin will destroy the arduino board. That's why the motor driver is necessary).

3. HC-06/HC-05 Bluetooth Module

4. LM35 Temperature Sensor(for measuring the temperature of environment)

5. Peltier Module(It's used for heating and cooling. Learn more about it)

6. Heat sink

7. Velcro Straps/Wrist Watch belts

8.Jumper Wires

9.Battery(I have used a pair of Nokia BL-60 batteries connected in series.You can use any kind of battery more than 5 volts and give sufficient current to run it.I think LI-PO batteries will be a better choice).

10.A Blue And Red Led (For indicating if the device is cooling or heating)

11.Thermal paste/Heatsink compound


1.Glue Gun

2. Scissor


Step 2: Making the Wristband(Part-1,Attaching the Peltier With the Heatsink)

Now it's turn to make the wristband. At first you have to attach the peltier with the heatsink.

So take the peltier and the heatsink. Put some thermal paste at the back of the heatsink and attach the hot side of peltier with the heatsink like the picture. Now mount the peltier with hot glue as shown in the picture.

Step 3: Making the Wristband(Part-2, Adding the Belt to the Wristband)

At first, take a rubber coated wire and the heat sink. Now put the wire to the gap of the heat sink like the pictures so that it creates D-shaped hooks on two sides of heat sink. Now use hot glue to join the wire with the heat sink more strongly so that the wire doesn't come out of the wristband.

Now take old watch belts or velcro straps and attach it to the hooks like the pictures by using hot glue.

Step 4: Design the Wristband However You Want

Now the wristband is ready. You can design it by using hot glue at the top of the heat sink to make it look more attractive.

(As my hot glue ran out, I couldn't design this wristband.So I have shown previously designed one in the pictures.)

Step 5: Circuit Diagram,Code and App:

Now Connect the components like the circuit diagram shown in the picture.

The connections are as follows:

1. Arduino Vin>>Motor Driver VCC and Battery.

2. Arduino 5V >> LM35 sensor's Vin

3. Arduino 3.3V>>Bluetooth module VCC

4. Arduino Tx>>Bluetooth module Rx

5. Arduino Rx>>Bluetooth module Tx

6. Arduino Pin 3>>Motor Driver In 1

7. Arduino Pin 5>>Motor Driver In 2

8. Arduino Pin 10>>Led Blue(+)

9. Arduino Pin 11>>Led Red(+)

10. Arduino Pin A1>> LM35 sensor's Vout

11. All components Ground>>Battery(-)

12. Motor Driver Out1>>Peltier(Red wire)

12. Motor Driver Out2>>Peltier(Black wire)

Download the code and android app:

[Note: Tx and Rx pin of bt module shouldn't be connected to arduino while uploading the code.]

Step 6: Box the Other Components

Now you need to put all other components in a box. Use a box which can be put in your pocket easily. But the box should have enough space to keep all the components.I used a mini plastic box. Put the arduino and other components inside the box. You can make separate area for battery. Make sure the indicator led s and the temperature sensor should be outside the box. The wires connected with the peltier should be long enough that you can keep the box in your pocket while wearing the wristband in your hand.

Step 7: And It's Ready

Now you have finished making this magical wristband. Now I'll explain you how to use it and how it works in the next steps.

Step 8: How to Use It

Download and install the app provided in step 4 in your smartphone. Turn on bluetooth in your smartphone. Turn on the device too.Now open the app and press the connect button and pair with HC-06/HC-05 bluetooth module . The device has three mode:

1.Auto Control

2.Manual Mode

3. Water Mode

1.Auto Control:

If you activate auto control by pressing auto control button , the wristband will heat or cool you according to the environment temperature. The device has a temperature sensor which measures the temperature of environment.The temperature will be displayed in your smartphone when you connect the device with your smartphone.If the temperature is more than 28°C,it will cool you and if the temperature is less than 25°C,it will warm you. The cooling rate and the warming rate depends on the temperature shown in the graph above.

2.Manual mode:

When you don’t feel satisfied with automatic mode, you can go through the manual mode using the sliders to cool or heat you according to your want . You can use the mode after physical work or gym to chill you up. The temperature of environment won't matter if you use the manual mode.

3.Water mode:

When you want to take bath in cold water or pond, you can activate water mode to warm you up and wait for 4-5 minutes and you will feel the water 1-2 degrees warmer than before. But it won't work effectively when water is too cold. But in case of cooling or heating, The wristband works like charm.

Now you can go to the next step to see how it works....

Step 9: How It Works

Now you may have a common question: How can cooling or heating such a small area of your body can cool your whole body??

In one sentence,the answer is: it doesn't change your body temperature like air conditioner or heater. Rather it's job is to keep you comfortable in rough weather.

Let me explain how the wristband works.You can assume that it’s cooling or heating your body.

But actually it’s not. Rather it changes your wrist temperature every second like the graph above which makes your brain to feel that the temperature is changing and you are in a hotter or cooler environment. The temperature increases for 6 seconds and the wristband turns off every second

Continuous temperature change on your wrist compels your brain to focus on your wrist temperature. So the other parts of your body doesn’t feel the environment temperature strongly. That’s why if your wrist is being warmed by the wristband, you will feel warm and if your wrist is being cooled, you will feel cool. You won’t feel the environment temperature exactly when you wear the wristband.

But if the temperature doesn’t keep changing, your brain will adjust with the temperature of wrist in a while and you will again start to feel the same though it will change your body temperature in a small rate.

Let me show a common example. When you keep hand in cold water,you immediately feel cool for a while.But after that your brain copes with the sudden temperature change and you don't feel cool anymore. In case of this wristband, it changes it's temperature every second. So your brain can't cope with the temperature and you feel cool as long as you wear the wristband. Moreover, the thermal sensors of wrist are stronger than the other part of body. Taking advantage of this,the wristband works more effectively

Changing the temperature of whole body is quite hard and needs a lot of energy. But this technique only changes your feeling about the thermal condition and makes you feel comfortable even in rough weather condition taking much less power.

Step 10: And You Are Done....

Though the wristband is cooling or heating a small area of body, it is quite effective. Even I will say not less than an air conditioner or heater. But the most wonderful thing is, it consumes not more than 2.5 Watts.

After wearing it, you will start to feel cool within a very short time. Even if the weather is too hot, you will feel that a gentle breeze is flowing continuously towards you.

I have tested the wristband on more than 50 persons in different temperature condition and all of them had positive response.

The wristband has long battery life along with it's portability. Just make it and take your control over the environment temperature.

If you are using manual mode, don't set the wristband too hot or cold.Set the slider position according to your want. Else you will start to feel more uncomfortable instead of feeling comfortable..

If you have any questions, you can give feedback to the comment sections. I'll try to reply as soon as possible.

Microcontroller Contest 2017

Participated in the
Microcontroller Contest 2017