Introduction: Smart Cap


In this instructable, I am going to introduce my new idea 'The Smart Cap.' I know many of you will have the question, What is smart cap and what exactly does it do?

Basically this is made by me, for my mother. My mother does miss a lot of phone calls when she’s travelling, not her fault, i can say that. It’s quite noisy in the city that I live. And so I decided to make something for her and there’s my idea. I actually made a cell phone signal detector and plugged in a motor that has a half metal disk on the end. The entire assembly is placed in the cap and is powered by a 9 volt battery.

When the cell phone receives or sends communication signals, The Smart Cap detects the signal and powers up the motor causing the cap to vibrate and not letting my mom to miss any calls,

This can also be very useful for senior elder people or the disables unable to hear.

Step 1: Components and Other Requiriments


LM360 X 1
LM741 X 1

BC 341 X 1

1.8m Ohms X 3
1K ohm X 1
10K ohm X 1
27k ohm X 1
Preset 500K ohm

104 X 4

2N222 X 1


9V X 1


Salvaged from a old PS2 controller


soldering Iron
Soldering Board.
spool of tread.
needle, Toogle Switch and some sponge sheet.

Step 2: Circuit Diagram

You need to make the circuit as shown above.

The above circuit can be differentiated in three different parts.

Firstly, the primary signal detecting circuit, the second one is inverting amplifier using Opamp LM741and the third one is a switching circuit using transistor.

More information on the working and making of the First circuit is given in the following link

This link will basically help you with working of the detector circuit and determining the length of antenna and values of the Resistors and the Pre-set

For the second part of the circuit i.e. inverting amplifier more information can be found in the following link

Basically you need to select the values of Rf quite high comparing to the value of R1 so that the gain of the amplifier is high and this will help in switching the transistor in on state.(I have Used R1 as 1K and Rf as 10K )

Step 3: Adjusting and Testing the Circuit

Different cell phones and the service providers have slightly different band and range.

First you need to adjust the Preset, so that when you receive a call only then the motor will be powered.

The point where the motor just does not get powered without a call will be the point you will set your Preset.

You need to try different lengths of the antenna and to set the range of your smart cap (Circuit at this stage.)

Typically you will set the range of your circuit of the distance from your pocket or your hand bag to your head.

I highly recommend testing the detector circuit first on the Breadboard using LED's. Adjust the Preset to the point where all the noise is filtered out. The Above video shows the Breadboard Model of My Detector circuit, which lights up the red LED when I receive the call. The above made circuit is made to detect 4G network on my mom's samsung galaxy A7.

Step 4: Soldering and Assembling

The circuit the circuit can now be soldered and can be placed in the cap.

The circuit is stitched in the Cap using tread and needle. I used the unused holes in the circuit board to stitch with the cap.

I also stitched the battery with the cap and also glued the Motor on the circuit board.

Step 5: Finalizing

You don't want to get irritated with the eaching caused by the circuit above your head, so the solution for that is to use a sponge based or a soft foam sheet. You can feel the toggle switch through the spongy sheet or you can also make a hole on the sheet if you like.

The sponge sheet is also stitched to the cap.

The Smart cap is now ready to use.

I'll love to listen from everyone, so be free and share your views, suggestions scope of improment etc.

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