Heart Rate Monitor Wiring diagram Schematic

Strictly speaking, this simple schema shouldnt work! How could anyone expect an ordinary light dependent resistor photo cell to see through a fingertip in natural daylight and detect the change in blood flow as the heart pulsates? The secret is a high gain schema, based on a dual op amp IC which can be either the low power LM358 or the JFET TL072. The LDR is connected in series across the 9V battery supply via a 100kO resistor (R1) and the minute signal caused by the blood pulsing under the skin is fed to the non-inverting (+) input, pin 3, of IC1a via a 0.µF capacitor.

Pin 3 is biased by a high impedance voltage divider consisting of two 3.3MO resistors. The feedback resistors to pin 2 set the gain to 11 times. The output of IC1a is fed via a 0.47µF capacitor and 220kO resistor to IC1b. This is configured as an inverting op amp with a gain of 45 so that the total schema gain is about 500. The output of IC1b is used to drive an analog meter which may be a multimeter set to the 10V DC range or any panel meter in series with a resistor to limit the current to less than its full-scale deflection. The prototype used an old VU meter with a 47kO resistor fitted in series.

Circuit diagram:

Heart Rate Monitor Circuit Diagram

Note that the unit was designed to use the Dick Smith Electronics light dependent resistor (Z-4801). Other LDRs may require a change in the value of resistor R1. A light source such as a high brightness LED is not required. All that is needed is a reasonably well-lit room, preferably natural daylight, to produce a healthy swing of the needle. Only when the hands are very cold does it make it a little more difficult to accurately count the pulses. To check your heart rate, carefully position your thumb or finger over the LDR and count the meter fluctuations for a period of 15 seconds. Then multiply the result by four to obtain your pulse rate. The schema can not be used if you are walking or running, etc.

Heart Beat Monitor Sensor

Heart Beat Monitor Sensor Circuit diagram : Here is a simple and low-cost cir-cuit of heart beat monitor using readily available components. It uses the piezo electric plate of audible piezobuzzers as the sensing device, which can be purchased for around Rs 2 only from component vendors.  The sensor is pressed against human body near the heart region. It should make a solid contact with your palm to convert heart beat sound into low-frequency electrical variations. These electrical variations are  amplified by transistor T1 that is configured as a common-emitter amplifier. Amplified signals are coupled to tran sistor T2 for driving the audio power amplifier stage. The speaker reproduces heart beat notes as audible sound. 

Heart Beat Monitor Sensor Circuit diagram :

Heart Beat Monitor Circuit-Diagram

The two BEL188 silicon transistors used in the power output stage are freely available. In case you use AC188/128 germanium transistors in place of BEL188 silicon transistors, replace 220-ohm resistors with 47-ohm resistors and 680-ohm resistors with 1-kilo-ohm resistors. 

Author : Pradeep G. - Copyright : EFY

Heat Detector Alarm using UM3561

A very simple heat detector alarm electronic project can be designed using the UM3561 sound generator schema and some other common electronic parts . This heat detector electronic schema project uses a complementary pair comprising npn and pnp transistor to detect heat Collector of T1 transistor is connected to the base of the T2 transistor , while the collector of T2 transistor is connected to RL1 relay T3 and T4 transistors connected in darlington configuration are used to amplify the audio signal from the UM3561 ic.

When the temperature close to the T1 transistor is hot , the resistance to the emitter –collector goes low and it starts conducting . In same time T2 transistor conducts , because its base is connected to the collector of T1 transistor and the RL1 relay energized and switches on the siren which produce a fire engine alarm sound. This electronic schema project must be powered from a 6 volts DC power supply , but the UM3561 IC is powered using a 3 volt zener diode , because the alarm sound require a 3 volts dc power supply. The relay used in this project must be a 6 volt / 100 ohms relay and the speaker must have a 8 ohms load and 1 watt power.

Streampowers

Two Basic Motor Speed Controllers

Here are two simple 12V DC motor speed controllers that can be built for just a few dollars. They exploit the fact that the rotational speed of a DC motor is directly proportional to the mean value of its supply voltage. The first schema shows how variable voltage speed control can be obtained via a potentiometer (VR1) and compound emitter follower (Q1 & Q2). With this arrangement, the motor’s DC voltage can be varied from 0V to about 12V. This type of schema gives good speed control and self-regulation at medium to high speeds but very poor low-speed control and slow starts. The second schema uses a switchmode technique to vary motor speed.

Circuit diagram:

Fig.1: a very simple motor speed controller based on a compound emitter follower (Q1 & Q2).

Here a quad NOR gate (IC1) acts as a 50Hz astable multivibrator that generates a rectangular output. The mark-space ratio of the rectangular waveform is fully variable from 20:1 to 1:20 via potentiometer VR1. The output from the multivibrator drives the base of Q1, which in turn drives Q2 and the motor. The motor’s mean supply voltage (integrated over a 50Hz period) is thus fully variable with VR1 but is applied in the form of high-energy "pulses" with peak values of about 12V.

Two Basic Motor Speed Controllers Circuit diagram:

Fig.2: this slightly more complicated schema gives better low speed control and higher torque.

This type of schema gives excellent full-range speed control and gives high motor torque, even at very low speeds. Its degree of speed self-regulation is proportional to the mean value of the applied voltage. Note that for most applications, the power transistor (Q2) in both diagram will need to be mounted on an appropriate heatsink.

Author: Ravi Sumithraarachchi - Copyright: Silicon Chip Electronics