Electronic Timer Switch - TIMER PROJECTS

Electronic Timer Switch

This electronic timer switch project is a good project to build to simulate the presence of occupants in a house. In these days when security is becoming more of a concern when no one is at home, having this device will deter the thief from breaking in. When power up, after 60 minutes, the relay will turn ON for 100 secs, OFF for the next 100 secs, and ON again for 100 secs before OFF again for the next 60 mins. This sequence will be repeated. A device such as a lamp that is connected to the relay will turn ON and OFF according to this timing.

Schematic Diagram

The schematic of the project is as shown below.

The core of this electronic timer switch project uses a CD4060B binary counter. The binary counter has 10 outputs and the counter are counted by configuring the oscillator. Every negative clock will trigger the counter of the IC internally.

The timing of the circuit is affected by resistor R3(1M ohm) and capacitor C2(0.1uF). By connecting the four outputs in an AND configuration, the transistor Q1 will only turn ON if all the 4 outputs are in logic "1". If any of the logic is "0", the transistor will remain OFF.

For a complete cycle, the transistor will be ON twice when the output at pin 15, QJ goes to logic "1" and "0" twice when the other outputs QL, QM and QN remain at "1". When this happen, the relay K1 will switch status accordingly. The timing of the switching can be changed by changing the resistor values R2, R3 and C2. Download the data sheet of CD4060B from Texas Instrument website for more details.

Note that since the oscillator is not using crystal, the timing may not be as accurate compared to the ideal calculation. In most cases, fine tuning the resistor and capacitor are good enough to make this project a success. To check whether the circuit is working, connect a LED in series with a 390 ohm resistor at output QD. It will flash ON and OFF as the oscillator oscillates.

Parts List

BASIC ELECTRONICS-TIMER CIRCUIT DESIGN

Introduction
Timer circuit has been used in many projects and there are basically 2 types that are used these days. One of them is the use of analog RC circuit where charging of the capacitor circuit determined the T(time) of the circuitry. This type of circuitry has larger tolerance and is used in applications where the T is not so critical as the T is affected by the tolerance of the RC components used.
The other is the use of crystal or ceramic resonators together with microprocessor, microcontroller or application specific integrated circuit that need higher precision T in the tolerance of up to 5 ppm (parts per million).



555 IC
One commonly used circuit is the 555 IC which is a highly stable controller capable of producing timing pulses. With a monostable operation, the T(time) delay is controlled by one external resistor and one capacitor. With an astable operation, the frequency and duty cycle are accurately controlled by two external resistors and one capacitor. The application of this integrated circuit is in the areas of PRECISION TIMING, PULSE GENERATION, TIMING DELAY GENERATION and SEQUENTIAL TIMING.
A typical 555 IC block diagram is as shown below.





 

Monostable Operation

Figure below shows the monostable operation of a 555 IC.





In this mode, the device generates a fixed pulse whenever the trigger voltage falls below Vcc/3. When the trigger pulse voltage applied to pin 2 falls below Vcc/3 while the its output is low, its internal flip-flop turns the discharging transistor Tr off and causes the output to become high by charging the external capacitor C1 and setting the flip-flop output at the same instant. The voltage across the external capacitor C1, VC1 increases exponentially with the time constant T=RA*C1 and reaches 2Vcc/3 at td=1.1RA*C1. Hence, capacitor C1 is charged through resistor RA. The greater the time constant RA*C1, the longer it takes for the VC1 to reach 2Vcc/3. In other words, the time constant RA*C1 controls the output pulse width. When the applied voltage to the capacitor C1 reaches 2Vcc/3, the comparator on the trigger terminal resets the flip-flop, turning the discharging transistor Tr on. At this time, C1 begins to discharge and its output goes to low.

Astable Operation




An astable operation is achieved by configuring the circuit as shown above. In the astable operation, the trigger terminal and the threshold terminal are connected so that a self-trigger is formed, operating as a multivibrator. When its output is high, its internal discharging transistor Tr turns off and the VC1 increases by exponential function with the time constant (RA+RB)*C. When the VC1, or the threshold voltage, reaches 2Vcc/3, the comparator output on the trigger terminal becomes high, resetting the F/F and causing its output to become low. This in turn turns on the discharging transistor Tr and the C1 discharges through the discharging channel formed by RB and the discharging transistor Tr. When the VC1 falls below Vcc/3, the comparator output on the trigger terminal becomes high and the timer output becomes high again. The discharging transistor Tr turns off and the VC1 rises again. The frequency of oscillation is given as below.

HOW TO MAKE A HEART RATE SENSOR?-BIOMEDICAL PROJECTS

I HAVE  ARRANGED A SCHEMATIC ABOUT MAKING A HEART RATE SENSOR

DOWNLOAD THE CIRCUIT DIAGRAM FOR THE HEART RATE SENSOR

DOWNLOAD

SOMETHING MORE

Here is the inside of the light reflectance sensor (top) and a schematic drawing of it's circuitry (bottom). First, carefully remove the phototransistor as shown. Then, attach the three wires that we will connect to the heart sensor (show in bright yellow).

Hint: if you leave the leads from the phototransistor when you cut it off, you can attach the two corresponding wires directly to them, rather than to the circuit board itself.

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HOW TO MAKE INFRARED HEART PULSE MONITOR?-BIOMEDICAL PROJECTS

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I HAVE MADE A CIRCUIT ON HEART PULSE MONITOR

This circuit is given at the bottom

ABSTRACT FROM A PATENT ON HEART PULSE MONITOR

The invention herein described is intended to provide the user with a reliable heart rate monitor that is a completely self contained unit and is capable of providing accurate readings while the wearer is moving about. The use of piezoelectric sensing elements eliminates the power drain caused by LEDs and similar devices. The sensing element mounting means disclosed herein is devised to greatly reduce the noise introduced into the pulse signal by body motion. The use of optical sensors in a staring mode and optical sensors in a pulsed mode is also presented. The effects of noise are further reduced by employing digital signal processing algorithms to find the heart pulse intermixed with noise signals and present the heart pulse rate in beats per minute on a display. The resulting device permits the visual monitoring of the heart pulse rate in a human body in a consistent, error-free manner.

DOWNLOAD THIS PATENT FROM HERE

About the heart pulse monitor circuit

DOWNLOAD THE CIRCUIT DIAGRAM

THIS CIRCUIT DIAGRAM IS SELF EXPLANATORY

IF ANYONE NEEDS HELP THEN CONTACT THE ADMINISTRATOR

16 CHANNEL BRAIN TISSUE STIMULATOR-BIOMEDICAL PROJECTS

[caption id="" align="aligncenter" width="300" caption="Image via Wikipedia"][/caption]

SUMMARY OF PROJECT

The pathways of brain circuitry can be studied by delivering current impulses to
brain tissue and observing the tissue response.  The goal of this project is To
develop a current source to be used for in vitro stimulation of rodent neural
tissue. The current source must deliver independently controlled currents to 16
separate electrodes on a 16 microelectrode array.  In addition, the currents must
be controllable via TTL computer logic and have a short response time to the
initial signal.  The design described in this report uses a transformer to supply a
large isolated voltage to 16 circuits which will convert the voltage to an
appropriate current.  The current on each channel will be controlled by a
potentiometer which varies the magnitude of the impulse received from a TTL
computer signal.  When the computer program supplies an impulse, a
corresponding square wave current pulse will be applied to the tissue.

DOWNLOAD THE PROJECT FROM HERE

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MAKE YOUR OWN EEG DEVICE-BIOMEDICAL PROJECTS

Overview

An EEG signal is usually acquired through silver-chloride covered electrodes, though sometimes other materials like pure silver, tin, steel or gold are used. The signal amplitude is only a few microvolt and needs to be amplified several thousand times before it can be captured. Because it is faint, the signal can very easily drown in noise, particularily 50/60Hz hum from the mains which is transmitted capacitively (i.e by an electric field) from the wiring in your house.

To handle this, the signal is first amplified by a high quality instrumentation amplifier, which measures the voltage difference between two locations on the scalp. In the example in the previous section, we used C3 and P3. This ensures that a large percentage of the mains hum never enters the system, because the level of the mains hum on those two locations is essentially the same.

Afterwards the signal strength is increased further by normal amplifiers, and passed through a low-pass filter which minimizes distortion caused by so-called aliasing that may occur when the signal is converted to digital samples.

Below is the block diagram of one EEG amplifier channel, and the Right-leg driver (DRL-circuit).

Simplified block diagram of the ModularEEG amplifier

Some parts are not included here. The schematic gives you all the details if you are interested.

The EEG signal is picked up by the two topmost electrodes and passed through the protection circut. It serves two purposes: First, it protects the circuitry from electrostatic discharge (ESD) and second it protects the user from failing circuitry. In theory at least.

Leaving the protection circuit, the signal enters the instrumentation amplifier where it is amplified 12 times. After that, the signal is amplified about 40 times in a second amplifier stage. You can't see it in the diagram, but there is a reason for splitting the amplification into two steps like this. Between the two stages there is a high-pass filter which removes DC-voltage offsets.

Some electrode materials, such as gold or steel, are polarizable. This means that electric charge can accumulate on the surface of the electrode, building up a relatively large DC-voltage, sometimes several hundred millivolts if you are unlucky. In theory, you would amplify a 200mV signal 480 and get a 96 volt output. In reality, the circuitry can handle about 2.5V so the output signal would be stuck at at a maximally high or low level, usually +/- 2.5V and not contain any EEG. The highpass filter tries to solve this problem.

Finally, the signal is amplified 16 times more and lowpass filtered. The filtering is done to prevent aliasing effects later on, when the signal is digitized.

Below the signal amplifiers, and the filter, sits a third amplifier pointing the other way, seemingly sending a signal to the user. This is the right-leg driver. It is named like this for historical reasons. The driver is, and was, previously only used by ECG meters, which measures the electrical activity in the heart. During ECG sessions, the driver (also abbreviated DRL, for Driven Right Leg) is attached to the right leg, as far away from the heart as possible.

The purpose of the DRL is to reduce common-mode signals such as 50/60Hz mains hum, by cancelling them out. It replaces a ground electrode which older EEG designs use, and can attenuate mains hum up to 100 times more than the instrumentation amplifier can do by itself.

After the filtering, the signal is ready for acquisition by the analog-to-digital converter which in our case is located inside a microcontroller. The microcontroller sends the digitized EEG to a PC via a standard serial cable. To protect the user from electrical faults, the EEG device is electrically isolated from the PC and external power sources. The block diagram below shows this.DOWNLOAD MORE INFORMATION ABOUT THE PROJECT FROM THE LINKS BELOW

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