Elektronika analog


Dual Regulated Power Supply

In this circuit, the 7815 regulatates the positive supply, and the 7915 regulates the negative supply. The transformer should have a primary rating of 240/220 volts for
europe, or 120 volts for North America. The centre tapped secondary coil should be rated about 18 volts at 1 amp or higher, allowing for losses in the regulator. An application for this type of circuit would be for a small regulated bench power supply.

13 Volt 20 Amp PSU



This PSU has been especially designed for current-hungry ham radio transceivers. It delivers safely around 20Amps at 13.8V. For lower currents, a separate current limiting output, capable of 15ma up to a total of 20A has been added. The power transformer should be capable to deliver at least 25A at 17.5 to 20V. The lower the voltage, the lower power dissipation. The rectified current will be “ironed” by the C1, whose capacity should not be less than 40.000uF, (a golden rule of around 2000uF/A), but we recommend 50.000uF. This capacity can be built up by several smaller capacitors in parallel.The base of this design is a simple 12V regulator (7812). The output voltage can be brought to desired value (here 13.8V) by two external resistors (R5 and R6) using this formula:

U= 12(1+R5/R6)

The low currents (here 15mA) will keep the 7812 in its regular function. As soon as the current rises over 15ma, the voltage drop on R4 will “open” the Q3, actually handling the high output current. This is a PNP transistor (Ic>25) and current amplification factor of at least 20. The one that has been tested and proven here is the 2N5683.

The current limiting resistance RL, for the maximum output of 20 Amps should be 0.03 Ohms, rated at least 15W. You can use the resistance wire or switch several resistors in parallel, totaling the resistance/power values. Values for other currents can be calculated by the rule:


The RL and Q2 (3A PNP such as BD330) form a short circuit “automatic fuse”. As soon as the maximum current reaches 20Amps, the voltage drop over the resistor RL will open Q2, and thus limit the B-E Current of Q3. Parallel to Q2 is Q1, which lights the LED 1 whenever the current limiting circuit is active. When the “fuse” is active, the Q2 bridges the R3, so the full current would flow through the IC1, and damage it. Therefore the R4 is inserted, as to limit the IC1 current to 15mA. This makes it possible to run the IC1 without any cooling aid.

The LED 2 will light up every time the PSU is switched on.

There is an adjustable current limiter in parallel to the fixed output, thus providing adjustable current source for smaller currents.

This circuit is very simple too. You will notice that there is no current sensing resistor. But it is really there, in a form of the Rds-on resistance of the N-channel FET, which actually handles the load cutoff from the source. The function of the FET is shown in the diagram 2. When the current Id is rising, the tension Uds over the resistance Rds rises very slowly in the beginning, but very fast after the knick.

This means, that before the knick the FET behaves as a resistor but after it, works as constant current source.

The D2, R3 and B-E connection of the Q4 will sense the Uds voltage of the FET1. When the voltage rises enough, the Q4 will shortcut the FET1 gate to mass, and cut the current flow through the FET 1 off.

However, to enable the FET1 to open, there is certain gate voltage necessary, which in this case is brought up by the voltage divider consisting of R8, Z1, P1 and R9. So the maximum Gate voltage will be the one of the Z1, and the minimal will be around 3V6.

The Z1 voltage (Uz1) will thus determine the max current flowing through the FET 1.

The diagram 2 will show that for 5 Amps the Uz1 should be 5V6, and for 20Amps around 9V6.


LM317 Regulator Circuit


The components are:

R1: 270R
R2: 2K Cermet or carbon preset potentiometer
C1: 100nF
C2: 1uF tantalum
LM317T Voltage regulator
PCB board

I also added DC power jacks for input and output on my voltage regulator, a green power LED, and a red over-voltage LED. The over voltage LED uses a zener diode to switch on the LED at a certain preset voltage, this can be varied depending on the voltage of the zener diode, I used a 6.2v zener diode. If you plan to vary the voltage for the different items you power, don't bother adding this feature. If you only plan to use items that run on one voltage, this is a very useful feature and will save plugging in and damaging your valuable (or not so valuable) equipment. You can even add a relay to switch off the power if the over voltage LED turns on, but bear in mind it will have to work from the voltage of the zener diode right up to the input voltage. I couldn't add a relay because I couldn't find any that operated from 6.2-13.8 volts.




Variable Power Supply

Using the versatile L200 voltage regulator, this power supply has independent voltage and current limits. The mains transformer has a 12volt, 2 amp rated secondary, the primary winding should equal the electricity supply in your country, which is 240V here in the
UK. The 10k control is adjusts voltage output from about 3 to 15 volts, and the 47 ohm control is the current limit. This is 10mA minimum and 2 amp maximum. Reaching the current limit will reduce the output voltage to zero. Voltage and current regulation equations can be found at this page.



Regulated 12 Volt Supply



Nicad Battery Charger

This simple charger uses a single transistor as a constant current source. The voltage across
the pair of 1N4148 diodes biases the base of the BD140 medium power transistor. The base-
emitter voltage of the transistor and the forward voltage drop across the diodes are relatively stable.  The charging current is approximately 15mA or 45mA with the switch closed. This
suits most 1.5V and 9V rechargeable batteries.
The transformer should have a secondary rating of 12V ac at 0.5amp, the primary should be
220/240volts for Europe or 120volts ac for North America.

The 741 Op Amp Comparator Circuit

This circuit utilises the 741 Op-Amp in 'Comparator' mode. This allows it to compare two input voltages via two different 'potential deviders'. The potential deviders will devide the voltage between the resistor and LDR. The LDR which has the most light on it will give the largest Voltage output. This can bwe summed up by: If Vout=+7V then LED 1 will light (Vb>Va) If Vout=-7V then LED 2 will light (Va>Vb) Therefore if more light is shining on LDR.1 than LDR.2 the left LED will light and vice versa.The reason why 7V is used rather than 9V is because the 741 OP-AMP is not 100% efficient, and 7V is usually outputed instead of 9V. The values of the 10K resistors will determine the sensativity of the circuit, so change these values where appropriate or add two potentiometers in their places.

Parts List

  • 1 741 Operational Amplifier
  • 2 Resistors- between 1k and 10k
  • 2 330 ohm resistors
  • 2 LDRs (Light Dependant Resistors)
  • LEDs
  • 2 9V power supplies
  • Bread board or similar

Mini Alarms

Sw1 is drawn as either a micro-switch or a magnetic-reed contact; but so long as it does the job you can use whatever type of switch you like. Use more than one switch if it suits your application. The output device is a "piezo" buzzer, requiring a current of about 10mA. Provided the buzzer's voltage is suitable, the circuits will work from 5 to 15-volts. The main features of each alarm are described on the circuit diagram itself. Each pair of circuits will print out on an A4 sheet.

The Cmos 4093 is the Schmidt-trigger version of the Cmos 4011. For present purposes the two are interchangeable. However, the 4093 has an improved switching performance that is most noticeable if the time periods are substantially extended.
The precise length of any time period will depend on the characteristics of the actual components used; especially the tolerance of the capacitors and the exact switching points of the Cmos Gates.

In the case of circuits 11 & 12, treat the values of R6 & R7 as a rough guide. The switching point of Gate 3 and the characteristics of the thermistor will determine the actual temperature range available. Changing the value of R6 will allow you to access different areas of the temperature scale; while changing the value of R7 will allow you to alter the width of adjustment available.
Although they are described as alarm circuits, they will have other applications. The buzzer may be replaced by a small relay or an optical isolator; and the timing components may be changed to produce the required output performance. Any relay should have a coil resistance of at least 270 ohms; but for battery operation, the higher the better. If you're using an optical isolator, connect a 1k resistor in series with its LED.

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Speaker Protector

This is a simple circuit which I built to one of my audio amplifier projects to control the speaker output relay. The purpose of this circuit is to control the relay which turns on the speaker output relay in the audio amplifier. The idea of the circuit is wait around 5 seconds ofter the power up until the spakers are switched to the amplfier output to avoid annoying "thump" sound from the speakers. Another feeature of this circuit is that is disconnects the speaker immdiatly when the power in the amplifier is cut off, so avoinding sometimes nasty sounds when you turn the equipments off.

circuit diagram

Component list

C1    100 uF 40V electrolytic
C2    100 uF 40V electrolytic
D1    1N4007
D2    1N4148
Q1    BC547
R1    33 kohm  0.25W
R2    2.2 kohm 0.25W
RELAY 24V DC relay, coil resistance >300 ohm

Circuit operation

Then power is applied to the power input of the circuit, the positive phase of AC voltage charges C1. Then C2 starts to charge slowly through R1. When the voltage in C2 rises, the emitter output voltage of Q1 rises tigether with voltage on C2. When the output voltage of Q2 is high enough (typically around 16..20V) the relay goes to on state and the relay witches connect the speakers to the amplifier output. It takes typically around 5 seconds after power up until the relay starts to condict (at absolute time depends on the size of C2, relay voltage and circuit input voltage).

When the power is switched off, C1 will loose it's energu quite quicly. Also C2 will be charged quite quicly through R2. In less than 0.5 seconds the speakers are disconnected from the amplifier output.


Operational Amplifier- Non-Inverting2

Operational Amplifier- Non-Inverting1

Operational Amplifier-Inverting2












Stereo encoder

Devrenin Fotografi




Devreye Ayit sema

Devrenin Componentleri yerlesmis Baski Devresi

Baski Devresi




2x      uA741

1x      4066

1x      TL074

1x      4027

1x      74LS390

1x      74LS00

1x      78L05


1x      150R

2x      390R

1x      470R

2x      560R

1x      680R

1x      1k

11x     1k8

1x      6k8

6x      10k

4x      12k

1x      15k

1x      22k

5x      33k

4x      47k

2x      560k

1x      trimr lezaty 1k (ne Piher)

1x      trimr lezaty 10k (ne Piher)

2x      trimr lezaty 100k (ne Piher)


1x      47pF styroflex

1x      100pF

1x      120pF styroflex

1x      330pF folie

3x      470pF styroflex

1x      680pF

1x      1nF folie

2x      1.2nF folie

1x      2.2nF

1x      4.7nF

4x      10nF

6x      100nF

2x      4.7uF tantal

3x      10uF tantal

3x      10uF

1x      47uF

1x      kap.trimr 40pF


3x      patice na IO 14

2x      patice na IO 16

2x      patice na IO 8




Analog to Digital Conversion


To be able to implement analog to digital conversion using the ADC0804LCN 8-bit A/D converter. You will design a circuit and program the chip so that when an analog signal is given as input, the equivalent digital voltage is displayed on an LCD display. Thus, in effect, your circuit should function like a simple voltmeter.

The ability to convert analog signals to digital and vice-versa is very important in signal processing. The objective of an A/D converter is to determine the output digital word corresponding to an analog input signal.

The Datasheet for ADC0804LCN shows the pinout and a typical application schematic. The A/D converter operates on the successive approximation principle. Analog switches are closed sequentially by successive-approximation logic until the analog differential input volatge[Vin(+) - Vin(-)] matches a voltage derived from a tapped resistor string across the reference voltage.

The normal operation proceeds as follows. On the high-to-low transition of the WR input, the internal SAR latches and the shift-register stages are reset, and the INTR output will be set high. As long as the CS input and WR input remain low, the A/D will remain in a reset state. Conversion will start from 1 to 8 clock periods after at least one of these inputs makes a low-to-high transition. After the requisite number of clock pulses to complete the conversion, the INTR pin will make a high-to-low transition. This can be used to interrupt a processor, or otherwise signal the availability of a new conversion. A RD operation(with CS low) will clear the INTR line high again. The device may be operated in the free-running mode by connecting INTR to the WR input with CS=0.

Since this is an 8-bit A/D converter, a voltage from 0-5V. O will be repersented as 0000 0000 (0 in decimal) and 5V is represented as 1111 1111 (256 in decimal). To convert a value X volts to decimal, use the following formula:

          X * 5.0

To get a better resolution, and display the vlaue as a floating point number, you can multiply the numerator by a factor of 100, 1000 etc. and then print the voltage accordingly.


  1. Interface the ADC0804LCN to the 8051
  2. Vary the voltage to Vin(+)
  3. Output the digital value of the voltage on the LCD

Apparatus Required:

  1. ADC0804LCN
  2. 10k resistor
  3. 1k resistor
  4. 150 pF capacitor
  5. LCD
  6. 12 MHz crystal
  7. 5V power supply
  8. Philips PDS51 development board


Figure 1. Pinout

Figure 2. A/D Schematic


#include <reg51.h>
#include "io.h"
sbit READ = P3^2; /* Define these according to how you have connected the */
sbit WRITE = P3^3;/* RD, WR, and INTR pins                                */ 
sbit INTR = P3^4;
void main( void ) {
        unsigned char adVal;
        unsigned long volts;
        READ = 1;
        WRITE = 1;
        INTR = 1;
        while(1) {
               /* Make a low-to-high transition on the WR input */
               while( INTR == 1 );    /* wait until the INTR signal makes  */
                                      /* high-to-low transition indicating */
                                      /* completion of conversion          */
                /* Read the voltage value from the port */              
                READ = 0;
                adVal = P1;
                READ = 1;
                /* Compute the digital value of the volatge read */
                /* Print the value of the voltage in decimal form */


  1. Wire up the circuit as shown in the schematic.
  2. Edit, compile and run your program using PDS51.
  3. You need 2 voltage sources:
    • You need 5 volts to power the A2D chip, LCD, and eventually for the stand alone microcontroller.
    • The second voltage source will vary, this is the voltage source which you are measuring. NOTE: Do NOT turn input voltage higher than 5V or you may damage the ADC080X chip.
  4. Burn a chip and replace it with the emulator in your circuit.

Building a Basic Stamp II Temperature Logger using Visual Basic 5.


This project will show you how to build Temperature Logger using a Stamp II connected to a PC serial port. I was planing on using the DS1620, but used a LM335 temperature sensor because it only needs a two wire interface and it is easy to waterproof. All i did to waterproof it was to put some heat srink tubing around the 3 wires then around the hole sensor.

Here is a screen shot of the Visual Basic 5 Program. The program still has some bugs, but its just error trapping things, like clicking the connect button with no com port selected will give you a error. I will fix that later, or you can do it your self. The software is available to anyone who wants it, feel free to modify it and way you wish. This program is made in Visual Basic 5, but will work fine in Visual Basic 6.

The program will update the current temperature every one second on the PC screen and will save it to a txt file on the Hard Drive every five minutes, along with the time and date. It will also display max and min temperature and max and min pressure for a 24 hour period, and plots pressure and temperature for a 24 hour period.

Weather Monitor logger Schematic

The LM335 is a presision temperature sensor, its output is a linear relationship (10mV/Kelvin). The LM335 is a zener diode that its voltage drop across increase as temperature increases. Note that there is a 2.2 Kohm current limiting resistor. Without the limiting resistor the LM335 will have to dissipate too much heat and increase the temperature reading. The formula for calculating the output of the LM335 is

Temp(in C) = (Vout*100)-273.15

To convert that to F it would be

Temp(in F) = (temp*1.8)+32

From a range of -20C(68F) to 45C(113F) the output range is about 1.3V's. However the ADC has a range of 4.096V, which is fine but if you would like to get a better resolution(more accurate temp reading) you could use a op amp circuit to make the output votlage be 0 V at -20C and 4V at 45C. Connecting it directly will, however, give you 0.1 C/1mV or .05F/1mV which is very good, but the opamp circuit would be more work, but would give you close to .01F/1mV. I dont think it really worth it , but i just thought i might mention it. I also just added a MPX4115 pressure sensor to monitor pressure as well, but i havnt updated the schematic with yet.

Note that i didnt show the connection to the PC, this is showen on the intro page.

1 Kb BASIC Stamp II Code
3 Kb Visual Basic 5 Code
0 Kb Templogger Setup program Coming soon.
100 KbDatasheet

 for the LM335


Water Activated Relay

Circuit : Marin Lukas, Croatia


Notes (English follows) :
Ovaj sklop je projektiran da ukljuci relej kada se na knotaktima pojavi voda.Tranzistor T1 moze biti zamijenjen s 2N2222A.Tranzistor T2 mora biti BC108. Na kolektor tranistora T1 osim releja mogu biti spojeni signal injektor, LE dioda, zarulja i ostali signalizacijski elementi.

In his circuit Marin has used two transistors wired as a high gain compound pair. Transistor T1 may be a 2N2222A and T2 a BC108. The current gain will be the product of each transistors beta, which will be a minimum of 140 x 110 or 15400. The power supply used can be any voltage from 4.5 to 15 volts, a typical 5 volt relay may require 60 mA to operate, in which case any fluid which passes a minimum current of 4 uA will activate the relay. This is easily achieved with tap or rain water

Electronic Doorbell with Counter

Circuit : Andy Collinson
Email: anc@mitedu.freeserve.co.uk

This circuit uses a synthesized sound chip from Holtek, the HT-2811. This reproduces the sound of a "ding-dong" chiming doorbell. Additionally, the circuit includes a CMOS 4026 counter display driver IC to count your visitors.

doorbell counter

Circuit Notes:
The Holtek HT-2811 is available from Maplin electronics in the UK, order code BH69A. The operating voltage must remain within 2.4 to 3.3 Vdc and standby current is minimal. The reset switch zeroes the count,and the 7 segment display is a common cathode type. To save power consumption the display can be enabled or disabled with a switch as shown in the above diagram. The count will still be held in memory. The IC pin out for the 4026 is shown in pin order below:

Pin 1 is the clock input
Pin 2 is the clock enable
Pin 3 is display enable
Pin 4 enables the carry output
Pin 5 is the carry output
Pin 6 is display segment f Pin 7 is display segment g
Pin 8 is 0 V.
Pin 9 is display segment d Pin 10 is display segment a
Pin 11 is display segment e Pin 12 is display segment b
Pin 13 is display segment c Pin 14 is the2 output
Pin 15 is reset
Pin 16 is +Vcc

The envelope of the chime is set by the 220k, 330k, 3u3 and 4u7 resistors and capacitors. These values are the manufactures default values, but may be adjusted to alter the length and delay of the chime.The combination of the 2k2, 22k and 47u resistor capacitor network has a double function. It provides a debouncing circuit for the bell press and at the same time has a sufficiently long time constant. This ensures that anyone rapidly pressing the doorbell switch, only advances the count once.The 47u capacitor may be increased in size, if needed.

Circuit Expansion:
The count may be expanded for up to 99 visits by cascading two CMOS 4026 IC's and using an additional 7 segment display. This is achieved by wiring pin 5 ( the 10's output ) of the first CMOS4026 to pin 1 (the clock input) of the second IC.

LCD thermometer

In this page, I introduce the LCD thermometer which is sold by "Akizuki Denshi Tsusho".
At this thermometer, the IC thermo sensor (S8100) or the diode (1S1588) is used as the thermo sensor. When using the IC thermo sensor, the thermometry to +100°C from -40°C is possible. Also, when using the diode, the measurement to +150°C from -20°C is possible. Both sensors are contained in the kit.
This time, I used the diode as the thermo sensor to measure more than +100°C.
ICL7136 of Intersil (Harris) is used for the thermometer and is measuring the change of the forward direction minute voltages of the diode by the temperature. The 3-1/2 digits liquid crystal display (SP521PR) is used for the display. The most significant digit can display only "1".
The consumption electric power of ICL7136 is very small and it is possible to operate about 3 months continuously with the 9-V cell.

The main parts are contained in the kit. The plastic case and the cell are contained. But, there is not a connection cable of the sensor.

Circuit drawing
of the LCD thermometer