Archive for the ‘Electronics’ Category

LED Emergency Lamp

June 16th, 2013 No comments

Here is the LED emergency lamp that’s being sold for few hundreds in the market.  See below for the pictures.  This lamp comes with 60+ LED lamps adding upto a power of ~4.5W.

I have attempted to reverse engineer the circuitry and drawn the circuit using ExpressSCH tool. Click on the image to see the full sized circuit.

All the components listed in the circuit are available in common electronics spares shops. 

Clicking noise from HDD??

April 22nd, 2013 No comments

Have you wondered replaced your hard drives (HDD), when there is “clicking” noise from the HDD?  When you hear that noise, it means the drive is performing a “hard-reset” internally.   I have always thought that the disk is a goner, when there is too much clicking noise from the HDD.

Lately, it was found that when the gave the HDD the 5 pin power cord, the clicking noise is gone.  In general, 4 pin power has <+12v, 0v, 0v, +5> and the 5 pin power cord has an additional 3.3v orange line.  Another discovery recently is that, the clicking noise is gone when I changed the SMPS.  When the SMPS is over loaded or so, I think it is not able to supply the current that the HDDs want, which in turn makes the HDDs to perform a hard reset internally.

So, before applying for a replacement HDD, please do try changing the power cord to a 5pin cord and when you cannot try replacing the SMPS.  Typically, when you have lot of devices in your machine, ensure you use a reasonably powerful SMPS to avoid outages.

Calculating Ampere-Hour AH requirement

May 20th, 2012 No comments
We are in a sorry state of erratic and long power cuts, due to shortage of power production by the nation against the increasing load conditions.  To add fuel to this fire, a wholesome of abled people putting their hard earned money on to power backup solutions, where they store the power during power availability and consume the stored power during outage.  On the whole, this looks simple and elegant, but this is not doing any good to the state, which shed’s power at different locations to balance against shortage in power production.  So theoretically, in a place where a family consumed 1kW per hour, would consume 2.5kW per hour during power availability and generate 1kW during power outage.  Yes, you are right. The equation is not balanced, because atleast 30-50% of power is wasted during the backup-retrieve cycle.

Ok, coming to the point.  What is the solution? Go for harvesting solar power, availability in abundance and omni present.  And most interestingly, rationed to perfection based on the amount of un-shadowed free space a family has.  I will just limit this article to calculating the battery provisioning when you go for a solar-inverter solution.  Let’s say I want to have a power backup for 2 hours and my load is 1kW. What would be the ideal inverter solution for this load condition?

Normal Power 1000 Watts
Power Factor 80 %
Inverter Rating 1000W/80% = 1250 VA
Number of Backup Hours 2 Hours
Energy To be Stored 1000×2=2000Wh
Inverter Battery Voltage 24VDC
Battery Amp-Hours 2000/24=83AH
Add @30% AH Margin 83*1.3=108AH~100AH

So, for this configuration you need a 1250VA Inverter with 2x12v 100Ah battery bank.  Let me explain the calculation,

  1. Power Factor: In AC (alternating current), Power = Voltage x Current x Power factor unlike in DC, Wattage = Voltage x Current.  Power factor is measure as the cosine of the phase angle between voltage waveform and current waveform.  For home use, the power factor will be 0>PF<1.  When PF is lower, the efficiency of the system suffers a lot.
  2. Battery Voltage: For 1250VA inverter system, the choice of battery bank is 24V instead of 12V.  The rationale for this choice is to limit the current from the battery to the inverter unit.  If you use a 12V battery bank, at full load there will be a current of 1250/12=104A flowing from the battery to the inverter.  You may have noticed the thickness of the battery wire be very high.  Despite that the power loss on those wires when the current is 100A, would be much higher than it is with 50A on a 24V system.  For a 24V system, the peak current shall be 1250/24=52A.  Also, at 100A, with 1m cable between battery and inverter, the impedance should be 0.00001 ohms.
  3. AH Margin: Although battery AH rating considers absolutely draining of the battery, we will not be able to do that for normal SMF battery.  Meaning, we should not discharge below 10V and likewise should not charge beyond 13.6V per 12V battery.  In order for the AH rating to work, we have to apply atleast 20-30% margin.

Solar Panel contd.

March 26th, 2012 14 comments







Installation of additional 130Wp is in place now to make the power plant worth 300Wp.  The new panel added has a spec of 17Vmp against the 16.4Vpm of the 170Wp panel group.  So eventually I may be losing some power.  I am using 10sqmm copper cable to reduce the transmission losses.  I had measured the impedance of the cable to 1mΩ. So at 20A, I will be losing about 0.4W only.  But the cost of this wire is around 70Rs/m.  I am able to produce about 221W during the mid day, and about 170W around 10AM.  Upon little bit of investigation, it is found that the solar panels shell out less power at increased temperature.  It is also said that at 60-70°C, the efficiency is around 70%, which is matching with my measurements.  So, thinking about a water cooling solution; basically augmenting a solar water heating solution with the solar panel to establish double benefits.  Every day with the solar panels is a day of new learning and I am enjoying it. 🙂

Temperature Monitoring Device

January 1st, 2012 No comments

LM35 Temperature Sensor

The System.

The monitor.

The mixed water line:

The hot water line:

The cold water line:

monitor opened up:

the atmega8 microcontroller

the lcd unit:


inside the monitor:

The AVR code.

const int COLD = 0, HOT = 1, MIXED = 2, CALIBRATE = 3;
const int PWMPORT = 5;

float SCALE = 5000.0/1024.0; // 10 bit resolution for ADC
const float LM35SCALE = 10; // 10mV per Centigrade

#include <LiquidCrystal.h>

LiquidCrystal lcd(13, 12, 11, 10, 9, 8 );

byte smiley[8] = {

float Calibrate( void )
  // write 5v to PWM port
  analogWrite(PWMPORT, 255);

  // read the 5v analog value in the calibrate port
  int val = analogRead(CALIBRATE);

  // read again the 5v analog value in the calibrate port
  val = analogRead(CALIBRATE);

  // whatever digital value we read is the range of output that we would get for 5v input.
  // so, set the scale appropriately.
  SCALE = 5000.0/(float)val;
  return SCALE;

void setup()
  lcd.createChar(0, smiley);
  float scale = Calibrate();

int Temp( int inADC )
  float lm35volts = (float)inADC * SCALE;
  float temp = lm35volts/LM35SCALE;
  return (int)temp;

int ReadData( int port )
  int data = -1;
  for ( int i = 0; i < 3; ++i )
    data = analogRead( port );
  return data;

void loop()
  int cold = ReadData( COLD );
  int hot = ReadData( HOT );
  int mixed= ReadData( MIXED );
  int cold_temp = Temp(cold);
  int hot_temp = Temp(hot);
  int mixed_temp = Temp(mixed);

  lcd.print( “C=” );
  lcd.print( cold_temp );
  lcd.print( ” H=” );
  lcd.print( hot_temp );
  lcd.print( “Mixed=” );
  lcd.print( mixed_temp );

Fixing a Hand Remote Control that doesn’t work!

December 4th, 2011 No comments
    It is hard to imagine a television or a multimedia system without remote control now a days. Broken remote control units is an eternal problem. Thanks to China for dumping remote control units, which makes the cost of them affordable between 60-75Rs for television units. But, finding a replacement for multimedia systems is still a problem as no vendor is holding such stocks for its lower sales.
     I have been hit for the same problem when my Altec Lansing 5.1 multimedia system’s remote control broke. In the sense, the remote was functional intermittently. And some time, the key pad mapping got goofed up with + working as – and so on. When I visited my local electronics stores guy, he said the general problem for intermittent remote operation is a conked up crystal that is found inside the remote control unit. 

    Remote control units work with Infrared light communication between the hand-unit and the multimedia system’s base unit.  Commands from the keypad are converted to IR signals, which are received and decoded by the base unit to perform appropriate function.  Since IR light is not visible to human eye, one should use a Camera eye to see the IR light.  The easiest way is to observe the LED mounted in the front of the hand unit through a mobile camera or any camera that’s in working condition.  The cameras bandwidth covers IR and UV apart from the visible spectrum.  You will find that the IR led blinks (carrier frequency is 22khz), when you press any button on the remote control unit.  If you observe that for some keys the IR led is not flashing or intermittently flashing, you may associate the problem to a faulty crystal in the remote control PCB.

    When the remote is opened, you will see a PCB like the one in the picture.  The PCB could be plucked out from the casing by hand.  You will also see a rubber like buttons which are the actual buttons that you press.  The rubber button is placed on the PCB, where the button presses are converted to switching action.  Remember, the buttons will have a conducting coating under it, which indeed closes the circuit when the button touches the PCB. 

    The crystal that comes as a part of the circuitry is shown in the picture.  It is otherwise called a ceramic resonator, which is the crucial component of an oscillator circuitry.  Crystals are typically used against LC, RC tank circuits for its very high stability feature against temperature and humidity. My remote uses a 455Khz crystal named CRB455E ( The cost of this crystal as on today is Rs 2 in Chennai/India.  After replacing the crystal, my remote is working perfectly so far.

Solar Battery Charger Cutoff Circuit

August 7th, 2011 4 comments

Using very few components, I have built a solar battery charger cutoff circuitry that would enable automatic cutoff of battery charging when the potential across the battery terminals reached a voltage level chosen by the preset setting in the circuit.  Medium power transistor is operated in Cutoff mode most of the time, so the quotient current of the circuit is fairly low in the order of few mA.  It should be noted that the Vopen-circuit of the solar panel is few volts higher than the voltage when the panel is connected across a load.  So, don’t adjust the preset without connecting the battery. When the circuit is turned on, the battery is directly connected with the solar panel, and hence the voltage perceived by the voltage divider is the load voltage.  When the voltage across the load goes beyond the set point, zener conducts to turn the transistor on, which would pull the relay down and break the charging circuit.  After the battery is disconnected, the voltage perceived by the potential divider circuit is the open-circuit voltage of the panel, which eventually creates a latch effect for the battery charger off condition.  The relay will be ON, till there is sun light and when in the dusk, the input voltage should drop below the threshold voltage to turn off the transistor.

There is a flaw in this circuit. 🙂

When the sun light drops, the relay turns off as the transistor is turned off.  But now, the battery potential will be again available across the potential divider circuit.   There is a potential, oscillation condition here!!

சூரிய ஒளி மின்சாரம் (Solar Electricity)

July 10th, 2011 5 comments

The completed Solar Panel mount structure.

Bottom side view of the panel.  The Panel is fully resting on the Iron frame constructed in the nearby fabrication shop based on my design.

This is my assistant Aakash, the boy next door.  He has been my aide for all the mechanical and automobile works.

The base frame of 30″ x 21″ with the center piece at 15″.

The base frame from perspective projection.  The center piece is a 5″ x 2″ 10mm plate welded at the center.  The holes are 10mm diameter drilled at 1″ and 3″ from the top and centered.

The main load bearing vertical pole measuring approx 2m and 2″ diameter.  The base plate is 6″ in horizontal length and 6″ on vertical depths.  The holes are 1/2″ and drilled at 3″ and 5″.

This is the solar panel bought from Akshaya Solar Pvt Ltd, AP.  The panel is rated 12v 70w and of dimension 1200mm x 21″ and weighting approximately 5kg.

The swing arm connecting the base frame and vertical pole.  The holes are 10 mm diameter and punched at 1″ and 3″ from the top.  The bottom pipe is 2.25″ diameter and about 5″ long.  The cross bolt is 0.5″ diameter.  This swing arm mounts on the pole on one side and attached to the base frame on the other side.  The base frame is pivoted on the top hole with swing setting using one of the 3 bottom holes.  The positions are provided to compensate of uttrayanam (north bound sun movement) and dakshanayanam (south bound sun’s movement).

The bottom link of the vertical pole.  This U link attaches to the parapet wall, which is 6″ is width and the cross bolts pass through the wall to lock the vertical plates.  The horizontal and the vertical plates are 6″x2″ and 10mm in thickness.

These are the bolts used.  The 1″ (4 nos) bolts are used to secure the solar panel on the base frame.  The 1.5″ bolts are used to secure the base frame to the swing arm.  The 4″ bolt is used to secure the swing arm to the vertical pole and the 8″ bolts are the bolts to secure the entire unit on the parapet wall by passing through the wall.

HT12E & HT12D Rosc values

May 1st, 2011 1 comment

Choosing a appropriate value of ROSC is critical for the functioning of HT12E and HT12D pair during Muxing and DeMuxing.  The following are the value pairs that are found to be working correctly at 5V power supply for both the ICs.  Although, they support variety of voltages, it is always better to keep them at the same voltage to avoid confusion on the internal oscillator frequency.  If the data sheet is seen, it becomes apparent that the internal oscillator frequency is function of (Vdd, Rosc).

1M 47K
1.1M 51K
750K 33K