Aug 25, 2016

Deep Soil Metal Detector Circuit - Ground Scanner

The post discusses a simple deep under soil metal detector circuit for evaluating hidden metals such as gold, iron, tin, brass etc by detecting change in the resistance of the relevant soil layers.

Bigger physical objects which might be buried within the topsoil could be unveiled through a modification in the electrical resistance of the soil layer at various depths. The design is about a device which may be for implementing relative enhancements on the resistance of the soil. This particular application can be particularly handy in archaeological excavations.

Deep Soil Metal Detector Circuit - Ground Scanner

The proposed deep soil metal detector instrument includes the measuring bridge (figure 1), the alternating voltage generator (fig 2) and the a couple of probes, sunken inside the soil.

The resistances across the soil layers, between the electrodes of probes are coupled to the input of the bridge arms, for measuring the parameters.

Prior to measurement through 100 ohm resistor may be adjusted for bridging the balance so that the dial instrument readings are initially at the minimal.

The design of the probe represented in FIG.3 may e understood as follows:

Each of the probes signifies the insulated rods having a diameter of around 1.5 mm. on the surface area of the bar along its axle, these are fixed electrodes in the form of six thin-walled tube, separated from each other.

Each electrode probe with the aid of six cable connection is attached to the switch S1 measuring bridge, that in turn hooks up with one of the six pairs of electrodes together with the bridge.

In this instance, each pair of electrodes at each of the positions of the switch S1 corresponds to the precise depth of the soil layer.

Soon after placing the probe on earth, in accordance with FIG. 4, the electrical resistance of the subsequent layers of soil located different depth is detected.

Evaluating the values acquired from the resistance, you are able to draw a conclusion at what depth (which soil layer) are objects that might be changing the resistance of the soil.

The space between the probes are pretty much decided on in each specific scenario. Occasionally, great outcomes could be obtained with distance that me approximately close to 2.4 m.

The variable resistor of the bridge is 500 ohms as shown in the deep soil metal detector circuit diagram, is for controlling the sensitivity of the bridge depending on soil type being investigated.

Courtesy: The Radio-Constructor, 1966, 8

Aug 24, 2016

IR Remote Control Circuit Using Arduino

In this post we are going to construct a customizable IR (infrared) based wireless remote control switch, which consists of IR remote and a receiver, you may modify according to your needs.

By: Girish Radhakrishnan

If you are above beginner level you can accomplish it with ease. The proposed circuit illustrated here just has three controls on remote and 3 relays on receiver end. You may modify the code and circuit diagram to fulfill your needs.

You’ll need two Arduino boards, which act as remote and another act as receiver. I would recommend Arduino pro mini for this project, since the sizes of them are pretty small and the overall size of the remote could be shirked.

You may use 3.3V based Arduino pro mini for remote so, that you can be powered with two button cell or two AA size batteries, according to your needs.

The IR transmitter circuit has 3 push to on buttons and an IR LED for sending commands to receiver. Each button has programmed with unique hexadecimal code, the same hexadecimal code is programmed on receiver side too.

When a button is depressed the IR LED sends out the hexadecimal code to receiver, the receiver will recognize which of the button is pressed and it switches the corresponding relay ON/OFF.

The proposed remote uses RC5 protocol for communicating with receiver; you may change everything by modifying the code.

If you are just beginner in Arduino, you can still accomplish it just follow the diagram and upload the code without modifying.

The circuit and program:

Arduino Remote Transmitter:


The above circuit illustrates how to build the Arduino IR remote transmitter.

The three 10K resistors are pull down resistors, which prevent accidental triggering of the remote due to static charge and a 220ohm current limiting resistor is employed for IR LED.

Program for Remote Transmitter:

//---------Program developed by R.Girish--------//

#include <IRremote.h>
IRsend irsend;
const int button1 = 4;
const int button2 = 5;
const int button3 = 6;
void setup() {
  pinMode(button1, INPUT);
  pinMode(button2, INPUT);
  pinMode(button3, INPUT);
void loop()
  if (digitalRead(button1) == HIGH)
  irsend.sendRC5(0x80C, 32);
  if (digitalRead(button2) == HIGH)
  irsend.sendRC5(0x821, 32);
  if (digitalRead(button3) == HIGH)
  irsend.sendRC5(0x820, 32);
 //---------Program developed by R.Girish--------//

Arduino Receiver:

The IR Arduino receiver  circuit as shown above consists of TSOP1738 sensor few transistors, current limiting resistors for transistor, relays and diodes for absorbing high voltage spike from relay coils.

The circuit diagram is self explanatory.

Program for Arduino receiver:

//-----------------Program developed by R.Girish-----------//
int input = 11;
int op1 = 8;
int op2 = 9;
int op3 = 10;
int intitial1;
int intitial2;
int intitial3;
IRrecv irrecv(input);
decode_results dec;
#define output1  0x80C    // code received from button A
#define output2  0x821   // code received from button B
#define output3  0x820  // code received from button C
void setup()
void loop() {
  if (irrecv.decode(&dec)) {
    unsigned int value = dec.value;
    switch(value) {
       case output1:
         if(intitial1 == 1) {       
            digitalWrite(op1, LOW);
            intitial1 = 0;          
         } else {                     
             digitalWrite(op1, HIGH);
             intitial1 = 1;         
       case output2:
         if(intitial2 == 1) {
            digitalWrite(op2, LOW);
            intitial2 = 0;
         } else {
             digitalWrite(op2, HIGH);
             intitial2 = 1;
       case output3:
         if(intitial3 == 1) {
            digitalWrite(op3, LOW);
            intitial3 = 0;
         } else {
             digitalWrite(op3, HIGH);
             intitial3 = 1;
//--------------Program developed by R.Girish-----------//

By following the above explanations you can accomplish three controls, if you want to add more controls and relay, you need to edit the code and circuit diagram.

You can assign output and input for unused pins in the receiver and remote in the program and connect number of transistor and relay for the respective pins in receiver and similarly connect number of switches and pull down resistor in remote.

You can use random hexadecimal code for assigning more number of buttons.

For example: 0xA235, 0xFFFF, 0xBA556 and so on. And also add the same hexadecimal value in receiver code too. For example: #define output4 0xA235, #define outout5 0xFFFF and so on.   

Aug 23, 2016

Natural Mosquito Repellent Circuit Using High Watt Resistor

As the name suggests, to build this simple natural mosquito repellent circuit you will just require a high watt resistor, a few drops of lemon eucalyptus oil and  mains supply input.

You might be already familiar with these popular ready made mosquito repellent units which come in the form of coils, liquids, mats etc, and most of us already use these products for keeping mosquitoes at bay.

Although these methods are effective and help our homes to get rid of dangerous mosquito transmitted diseases like dengue, malaria, hay fever, etc, the chemicals ( mainly DEET) used in these repellents in turn have the potentials to cause many unknown body ailments, which could include lung diseases, severe headache such as migraine etc.
Therefore using these ready made chemical based repellents may not be after all safe either.

An alternative and much safer way of driving away mosquitoes could be by using naturally available options, one of which is available by the name Lemon Eucalyptus Oil.

Lemon eucalyptus oil is extracted from the tree lemon eucalyptus and can be easily procured from any nearby chemist shop or may be ordered online.

Normally this oil is required to be applied on the exposed areas of the body in order to protect from mosquito bites, however it may be much cleaner and safe if its fragrance could be dispensed through in the air instead of applying on body. This could be probably done using a homemade fragrance dispenser circuit

To build the above suggested homemade mosquito liquid dispenser circuit, you would just need a high watt resistor, and a mains input supply.

The set up can be seen in the following diagram:

In the shown set up we can see a high watt resistor and an aluminum dish glues over the resistor.

The resistor leads are terminated into a mains 220V or 120V socket.

The aluminum dish is used for placing a piece of cotton wad drenched with lemon eucalyptus oil.

That's all, once this set up is built and plugged in, the high watt resistor could be seen heating up and enabling the aluminum dish to also heat up, causing the heat to evaporate the oil and its fragrance in the air.

This special fragrance which may not be harmful to humans but irritating for the mosquitoes would ultimately help to drive away the creatures away from our homes, naturally and without any health risks.



Aug 22, 2016

Incubator Temperature Controller Circuit using LM35 IC

A very simple egg incubator temperature controller thermostat circuit using LM 35 IC is explained in this article. Let's learn more.

An Incubator is a system where bird/reptile eggs are hatched through artificial methods by creating a temperature controlled environment. Here the temperature is precisely optimized to match the natural incubating temperature level of eggs, which becomes the most crucial part of the whole system.

The advantage of artificial incubation is faster and healthier production of the chicks compared to the natural process

Anybody involved in this profession will understand the importance of a temperature controller circuit which should be not only reasonably priced but also have features like precise temperature control and manually adjustable ranges, otherwise the incubation could get hugely affected, destroying most the eggs or developing premature offspring.

I have already discussed an easy to build incubator thermostat circuit in one of my earlier posts, here we'll learn a couple of incubator systems having easier and much more user friendly setting up procedures.

The first design shown below uses an opamp and a LM35 IC based thermostat circuit and indeed this looks quite interesting due to its very simple configuration:

 The idea presented above looks self explanatory, wherein the IC 741 is configured as a comparator
with its inverting pin#2 input pin is rigged with an adjustable reference potentiometer while the other non-inverting pin#3 is attached with output of temperature sensor IC LM35

The reference pot is used to set the temperature threshold at which the opamp output is supposed to go high. It implies that as soon as the temperature around the LM35 goes higher than the desired threshold level, its output voltage becomes high enough to cause pin#3 of the opamp to go over the voltage at pin#2 as set by the pot. This in turn causes the output of the opamp to go high. The outcome is indicated by the lower RED LED which now illuminates while the green LED shuts off.

Now this outcome can be easily integrated with a transistor relay driver stage for switching the heat source ON/OFF in response to the above triggers for regulating the incubator temperature.

A standard relay driver can be seen below, wherein the base of the transistor may be connected with pin#6 of the opamp 741 for the required incubator temperature control.

Incubator Temperature Controller Thermostat with LED Indicator

In the next design we see another cool incubator temperature controller thermostat circuit using an LED driver IC LM3915

In this design the IC LM3915 is configured as a temperature indicator through 10 sequential LEDs and also the same pinouts are used for initiating the ON/OFF switching of the incubator heater device for the intended incubator temperature control.

Here R2 is installed in the form of a pot and it constitutes the threshold level adjustment control knob and is used for setting up the temperature switching operations as per the desired specifications.

The temperature sensor IC LM35 can seen attached to the input pin#5 of the IC LM3915. With rise in temperature around the IC LM35 the LEDs begin sequencing from pin#1 towards pin#10.

Let's assume, at room temperature the LED#1 illuminates and at the higher cut-off temperature the LED#15 illuminates as the sequence progresses.

It implies that pin#15 may be considered the threshold pinout after which the temperature could be unsafe for the incubation.

The relay cut-off integration is implemented according to the above consideration and we can see that the base of the transistor is able to get its biasing feed only upto pin#15.

Therefore as long as the IC sequence is within pin#15, the relay remains triggered and the heater device is held switched ON, however as soon as the sequence crosses over pin#15 and lands on pin#14, pin#13 etc. the transistor biasing feed is cut off and the relay is reverted towards the N/C position, subsequently switching OFF the heater..... until temperature normalizes and the sequence restores back below the pin#15 pinout.

The above sequential up/down drift keeps on repeating in accordance with the surrounding temperature and the heater element is switched ON/OFF maintaining almost a constant incubator temperature as per the given specifications.

Aug 20, 2016

SG3525 Pure Sinewave Inverter Circuit

In this post we learn how to make a SG3525 pure sinewave inverter circuit using a straightforward PWM integration.

We know that the IC SG3525 is designed to produce a modified sine wave output when used in an inverter topology, and cannot be enhanced to produce a pure sinewave waveform in its typical format.

Although the modified squarewave or sinewave output could be OK with its RMS property and reasonably suitable for powering most electronic equipment, it can never match the quality of a pure sinewave inverter output.

Here we are going to learn a simple method which could be used for enhancing any standard SG3525 inverter circuit into a pure sinewave counterpart.

For the proposed enhancement the basic SG3525 inverter could be any standard SG3525 inverter design configured to produce an modified PWM output. This section is not crucial and any preferred variant could be selected (you can find plenty online with minor differences).

I have discussed a comprehensive article regarding how to convert a square wave inverter to a sinewave inverter in one of my earlier posts, here we apply the same principle for the upgrade.

How the Conversion from Squarewave to Sinewave Takes Place

You might be curious to know regarding what exactly happens in the process of the conversion which transforms the output into a  pure sinewave suitable for all sensitive electronic loads.

It is basically done by optimizing the sharp rising and falling square wave pulses into a gently rising and falling waveform. This is executed by chopping or breaking the exiting square waves into number of uniform pieces.

In the actual sinewave, the waveform is created through an exponential rise and fall pattern where the sinusoidal wave gradually ascend and descend in the course of its cycles.

In the proposed idea, the waveform is not executed in an exponential, rather the square waves are chopped into pieces which ultimately takes the shape of a sinewave after some filtration.

The "chopping" is done by feeding a calculated PWM to the gates of the FET via a BJT buffer stage.

A typical circuit design for converting the SG3525 waveform into a pure sinewave waveform is shown below. This design is actually an universal design which may be implemented for upgrading all square wave inverters into sinewave inverters.

As may be in the above diagram, the lower two BC547 transistors are triggered by a PWM feed or input, which causes them to switch according to the PWM ON/OFF duty cycles.

This in turn rapidly switch the 50Hz pulses of the BC547/BC557 coming from the SG3525 output pins.

The above operation ultimately force the mosfets also to turn ON and OFF number of times for each of the 50/60Hz cycles and consequently produce a similar waveform at the output of the connected transformer.

Preferably, the PWM input frequency should be 4 times more than the base 50 or 60Hz frequency. so that each 50/60Hz cycles are broken into 4 or 5 pieces and not more than this, which could otherwise give rise to unwanted harmonics and mosfet heating.

PWM Circuit

The PWM input feed for the above explained design can be acquired by using any standard IC 555 astable design as shown below:

This IC 555 based PWM circuit can be used for feeding an optimized PWM to the bases of the BC547 transistors in the first design such that the output from the SG3525 inverter circuit acquires an RMS value close to mains pure sinewave waveform RMS value.

Using an SPWM

Although the above explained concept would greatly improve the square wave modified output of a typical SG3525 inverter circuit, an even better approach could be to go for an SPWM generator circuit.

In this concept the "chopping" of each of the square wave pulses is implemented through a proportionately varying PWM duty cycles rather than a fixed duty cycle.

I have already discussed how to generate SPWM using opamp, the same theory may be used for feeding the driver stage of any square wave inverter.

A simple circuit for generating SPWM can eb seen below:

 In this design we see a standard IC 741 opamp whose input pins are configured with a couple of triangle wave sources, one being much faster in frequency than the other.

This forces the opamp to compare the two coinciding peaks of the waveforms and generate SPWM or sinewave PWM consisting of a proportionately widening and narrowing PWMs in each cycle.

When this optimized PWM is fed to the first circuit design causes the output from the transformer to produce a further improved and gentle sine waveform having properties much identical to a standard AC mains sine waveform.

However even for an SPWM, the RMS value will need to be correctly set initially in order to produce the correct voltage output at the output of the transformer.

Once implemented one can expect a real sinewave equivalent output from any SG3525 inverter design or may be from any square wave inverter model.

If you have more doubts regarding SG3525 pure sinewave inverter circuit you can feel free to express them through your comments.
Swagatam Majumdar
Swagatam MajumdarHi Friends, Welcome to my site, a place where you will discover a massive collection of electronic circuit ideas, mostly requested by the dedicated readers and exclusively designed by me for their customized application needs. I have posted more than 1100 circuit designs in this site, if you have a personalized circuit requirement you may feel free to request it through the comment box, if it seems feasible to me then surely you may find it published here with your credentials attached in the post, thanks and please keep reading

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