By: SS Kopparthy
This circuit is a simple idea of warning a person who is using this when they try to get down the bed by vibrating an small DC vibration motor attached to the person’s leg so that the person can be awakened due to vibrations and can get back to bed.
The sensor used to detect that person is out of bed is a pressure sensor that is home made using two square copper clad strips of side 6.5cm and a sponge of 2.5cm width placed between the copper strips.
This arrangement acts as a variable capacitor and the capacitance changes when the pressure applied on it changes and this is used to trigger IC 555 and vibrate the vibration motor through simple circuitry.
WORKING OF THE CIRCUIT:
The sleep walk alert circuit consists of a IC 555 which is heart of the circuit. Here the IC 555 is wired as a astable multi vibrator.
The pressure sensor used works as a variable capacitor and its capacitance varies when the pressure is applied. When no pressure is applied, the capacitance of the capacitor is less than 10pf.
When pressure is applied, the distance of separation between the copper clad strips capacitance is around 50pf.
This happens because the capacitance of a parallel plate capacitor is inversely proportional to distance of separation of the plates. Now, this variation in the capacitance makes the IC to trigger itself and the output at pin #3 of the IC goes high. This is connected to a relay whose contacts are used to run the vibration motor.
MAKING THE PRESSURE SENSOR:
You need two copper strips (6.5*6.5 length*breadth, applied with varnish and cleaned), a thick new sponge of 2.5cm thickness, two ordinary insulated flexible wires and a little amount of glue to stick the sponge between copper strips.
Take the copper strips and place the sponge between them and stick the sponge to the copper strips by gluing only on the sides. REMEMBER NOT TO GLUE IN CENTERS OF SPONGE OR STRIPS AS IT MAY DISTURB THE SENSOR AND YOU MAY NOT GET DESIRED OUTPUT.
After the glue gets dried, solder the insulated flexible wires to both the copper strips. You’ve completed making the sensor now. Just connect the wires to the circuit according to the circuit diagram.
USING THE ARRANGEMENT:
Take the circuit and enclose it in a suitable plastic casing. Also stick the vibration motor inside the plastic case using m-seal or any such.
Connect the circuit to a 9V battery and put the battery into the same plastic case as well. Put a small hole to the casing for the wires of sensor to come out of the case.
Now, take the pressure sensor and stick it to the bottom of a new sandal. Also, the plastic case containing the circuit, vibration motor and the battery is fitted to the a leg strap and the strap is worn above the ankle.
The strap and sandals are to be worn just before sleeping, so that is you get down the bed, it vibrates and you will be awakened.
A leg strap like the one shown in the image below can be used.
This might help you out in getting out of the habit of walking in sleep. But it is not an medical alternative. Good luck!
R1 - 100K(VARIABLE RESISTOR)
R2 – 4.7K (VARIABLE RESISTOR)
C1 – 0.01µF
C2 – PRESSURE SENSOR
D1 – 1N4001
RY1 – 9V RELAY
VIBRATION MOTOR – DC 6V VIBRATION MOTOR