Saturday, February 26, 2011

Op-Amp UA739 Dynamic Microphones Preamplifier

This is a low noise preamplifier circuit for dynamic microphones. The circuit is based on the Op-Amp UA739. The uA739 is a dual audio operational amplifier with high gain and excellent stability. Out of the two opamps available in the IC, only one is used here.

 UA739 Dynamic Microphones Preamplifier Circuit
The audio signals from the microphone are coupled to the non inverting input of IC1 through the capacitor C1 and resistor R1. C1 performs input DC decoupling. The R1, C2 network bypasses the unwanted high frequency signals from the microphone. A fraction of the output is fed back to the inverting input in order to prevent oscillations and ensure better stability. The input impedance of this circuit is around 50K.This amplifier can handle signal from 20Hz to 20 KHz, which makes it excellent for audio applications.
Detail download here

Tuesday, February 22, 2011

LED Pulser Circuit Using Op-Amp LM358

This circuit operates a LED in pulsing mode, LED goes from off state, lights up gradually, then dims gradually. This operation mode is obtained by a triangular wave generator formed by two op-amps contained in a very cheap 8 pin DIL case IC. Transistor Q1 ensures current buffering, in order to obtain a better load drive. R4 & C1 are the timing components: using the values shown in the parts list, the total period is about 4 seconds.
LED  Pulser  Circuit Using Op-Amp LM358
  • The most satisfying results are obtained adopting for R4 a value ranging from 220K to 4M7. Adopting for R4 a value below 220K, the pulsing effect will be indistinguishable from a normal blinking effect.
  • Voltage supply range can be 4 to 6V: 4.5V is the best compromise.

List Component of LED  pulser  circuit
R1,R2  : 4K7
R3     : 22K  
R4     : 2M2 1/4W (See Notes)
R5     : 10K 
R6     : 47R 
C1     : 1µF Polyester Capacitor
D1     : 5mm. Red LED 
IC1    : LM358 Dual Op-amp
Q1     : BC337 
Detail download here

Thursday, February 17, 2011

2-Transistor Electronic Touch Switch

A simple electronic touch switch can be constructed using this circuit diagram . This electronic touch switch circuit is based on 2-transistors an can activate a relay. Putting a finger on the touch pads turns the top transistor ON and this transistor turns on the bottom transistor. When the finger is removed, the circuit consumes less than a microamp.
2-Transistor  Electronic Touch Switch circuit
The touch sensor can be constructed using a small piece of a printed circuit board ( two small tracks with a 2 mm distance between each other ) . This circuit is powered using a 12 volts DC power supply , so the relay used for this project must be a 12 volts relay . This circuit is working very simple , when both plates of the sensor are touched the skin resistance will activate the circuit.
Detail download here

NE555 simples Touch Switch

The 555 can be used to create a Touch Switch. The only problem with this is the 555 consumes about 8mA, at all times when the supply is connected. This circuit is a simple touch plate controller which when touched on the touch plate operates the relay for a preset time then turns off automatically. This circuit has got applications in common equipments like touch operated doorbells, toys, buzzers etc. See below for an ON-OFF touch switch using a 555.
 NE555  simples Touch Switch Circuit
NE555 Pinout
The trigger pin of NE 555 has high input impedance. This property is exploited in this circuit in such a way that human body induced voltage is used for triggering this IC. When this IC is triggered, its output goes to high for a time duration determined by resistor R1 and capacitor C1. The relay used here is driven by a transistor. This relay contact is utilized here to drive loads like bell, lights, motor etc.

Note: To setup the circuit connect to power supply and adjust R1 while keeping touching on the touch plate and stop at the point where relay activates.
Detail download here

Saturday, February 12, 2011

CD40110BE - 4 Digit Up/Down Counter

This is a simple up down counter circuit that can be used of a large number of applications. The circuit is based on the IC CD40110BE which is a CMOS decade up/down counter.
CD40110BE - Up/Down Counter Circuit
Common cathode seven segment display is connected to the 7-segment output of each IC.Display connected to the IC1 represents the lowest number and display connected to IC4 represents the largest number. Synchronous counting is achieved by connecting BORROW and CARRY pins of the preceding stage IC to the CLK DOWN and CLK UP of the next stage IC. For UP counting trigger pulse must be given to the pin7 of IC1 and for down counting trigger pulse must be given to the pin9 of IC1.The RESET pins of all IC are shorted and they have to be connected to ground during normal operation. Connecting the RESET pins to positive supply using the switch S1 resets the counter.
Detail download here

4-Channel Audio Mixer Using Op-Amp 741

Here is a  simple 4 channel audio mixer  that has proved useful. Using this mixer alleviates the need to unplug and plug the various audio sources from the recorder input.
Circuit of 4-Channel Audio Mixer Using Op-Amp 741
The 4 inputs are connected to a summing network consisting of R1 to R4, each input has its own level control ( VR1 to VR4 ). The output of the summing network is connected to the inverting input of the 741 op amp which is configured as a inverting amplifier with a voltage gain of exactly 1, the feedback resistor R5 in conjunction with R1 - R4 ensures this. As the inverting input of the op amp is a virtual earth, each individual mixer input is completely isolated from all the other inputs. Up to fifty or so inputs could be used here providing the sum of all the voltages present on the mixer inputs never exceeds the supply rail of the op amp ( within two volts of supply using this op amp ). The non inverting input of the 741 is biased to half supply by R6 and R7. All of the summed or mixed signals appear on the output of the op amp pin 6 and they will be 180 degrees out of phase with the input signal, for this application the phase inversion is of no consequence here.

The output of the mixer is also fed to D1, D2, and TR1 which is a simple peak indicator. D1, D2, C7 and C8 form a charge pump circuit which rectifies the AC signal present on pin 6 of the 741 to an average DC level, this in turn is used to illuminate the LED via TR1. I adjusted the preset pot so the LED just starts to glow for an input of 2 volts peak to peak
Detail download here

Wednesday, February 9, 2011

Low Cost Siren Using 3-Transistor

This is a low-cost siren circuit to add to our range of alarm modules. This circuit generates a tone that sounds very similar to a siren.
Low  Cost Siren Using 3-Transistor Circuit
A complementary transistor pair (Q2 & Q3) is wired as a high efficiency oscillator, directly driving the loudspeaker. Q1 ensures a full charge of C2 when power is applied to the circuit. Pressing on P1, C2 gradually discharges through R8: the circuit starts oscillating at a low frequency that increases slowly until a high steady tone is reached and kept indefinitely. When P1 is released, the output tone frequency decreases slowly as C2 is charged to the battery positive voltage through R6 and the Base-Emitter junction of Q2. When C2 is fully charged the circuit stops oscillating, reaching a stand-by status.

  • A good sized loudspeaker will ensure a better and powerful output tone.
  • As stand-by current drawing is zero, SW1 can be omitted and B1 wired directly to the circuit.
List Component of Low  Cost Siren Circuit

R1,R3 : 1K         C1,C2 : 22µF/25V
R2,R5 : 10K C3 : 10nF
R4 : 220R C4 : 47µF/25V
R6 : 220K Q1,Q2 : BC557
R7 : 22K Q3 : BC337
R8 : 100K
SW1 : SPST Toggle or Slide Main Switch (See Notes)
P1 : SPST Pushbutton Operating Switch
SPKR : 8 Ohm Loudspeaker
B1 : 12V Battery
Detail download here

220 Volts Flashing Lamps

This circuit is intended as a reliable replacement to thermally-activated switches used for Christmas tree lamp-flashing.
220 Volts Flashing Lamps Circuit
The schematic diagram formed by Q1, Q2 and related resistors triggers the SCR. Timing is provided by R1, R2 & C1. To change flashing frequency do not modify R1 and R2 values: set C1 value from 100 to 2200µF instead. Best performances are obtained with C1= 470 or 1000µF and R4= 12K or 10K. Due to low consumption of normal 10 or 20 lamp series-loops intended for Christmas trees (60mA @ 230V typical for a 20 lamp series-loop), very small and cheap SCR devices can be used, e.g. C106D1 (400V 3.2A) or TICP106D (400V 2A), this last and the suggested P0102D devices having TO92 cases.

List Component of 220 Volts Flashing Lamps circuit
R1    : 100K
R2,R5 : 1K
R3,R6 : 470R
R4 : 12K
C1 : 1000µF/25V
D1-D4 : 1N4007
D5 : P0102D
Q1 : BC327
Q2 : BC337
PL1 : Male Mains plug
SK1 : Female Mains socket

Warning! The device is connected to 220Vac mains, then some parts in the circuit board are subjected to lethal potential! Avoid touching the circuit when plugged and enclose it in a plastic box.
Detail download here

2N3055|MJ2955 Class B Amplifier

This simple Class B Amplifier, straightforward but rugged circuit, though intended for any high quality audio application and, above all, to complete the recently started series of articles forming the Modular Preamplifier Control Center, is also well suited to make a very good Guitar or Bass amplifier.
2N3055|MJ2955  Class B Amplifier Circuit
Using a mains transformer with a secondary winding rated at the common value of 25 + 25V (or 24 + 24V) and 100/120VA power, two amplifiers can be driven at 45W and 69W output power into 8 and 4 Ohms respectively, with very low distortion (less than 0.01% @ 1kHz and 20W into 8 Ohms).

List Componet of 2N3055|MJ2955  Class B Amplifier circuit
R1      : 18K         D1,D2,D3,D4 : 1N4148
R2      : 3K9         Q1,Q2       : BC560C
R3,R6   : 1K          Q3,Q4       : BC556
R4      : 2K2         Q5          : BC546
R5      : 15K         Q6          : BD139
R7      : 22K         Q7          : BD140
R8      : 330R        Q8          : MJ2955
R9,R10  : 10R         Q9          : 2N3055
R11,R12 : 47R
R13     : 10R

C1      : 1µF/63V
C2      : 470pF
C3      : 47µF/25V
C4      : 15pF
C5      : 220nF
C6      : 100nF
Detail download here

Simple Adjustable Voltage Using 2-Transistor

A simple but less efficient method of controlling a DC voltage is to use a voltage divider and transistor emitter follower configuration.
Circuit of Simple Adjustable Voltage Using 2-Transistor
The schematic diagram above illustrates using a 1K pot to set the base voltage of a medium power NPN transistor. The collector of the NPN feeds the base of a larger power PNP transistor the which supplies most of the current to the load. The output voltage will from be about 0.7 volts below the voltage of the wiper of the 1K pot so the output of cans be adjusted from 0 to the full supply voltage minus 0.7 volts. Using two transistors Provides a current gain of around 1000 or more so That only a couple milliamps of current is drawn from the voltage divider to supply a couple amps of current at the output. Note That this circuit is much less efficient Than the 555 timer dimmer circuit using a variabe duty cycle switching approach.

In the schematic diagram above, the 25 watt / 12 volt lamp draws about 2 amps at 12 volts and 1 amp at 3 volts so the power lost Pls That the lamp is dim is around (12-3 volts * 1 amp) = 9 watts. A Fairly large heat sink is required to Prevent the PNP power transistor from overheating. The power consumed by the lamp will from be only (3 volts * 1 amp) = 3 watts Gives us the which an efficiency factor of only 25% Pls the lamp is dimmed. The advantage of the circuit is simplicity, and Also That it does not generate any RF interference as a switching regulator does. The circuit cans be Used as a voltage regulator if the input voltage Remains constant, but it will from not compensate for changes at the input as the LM317 does.
Detail download here

Wednesday, February 2, 2011

Simple Sine Wave Generator Based 2 Transistor

This Simple Sine Wave Generator circuit was designed to provide a valuable test equipment tool for sound reinforcement systems like guitar amplifiers and the like. Used in conjunction with an ac voltmeter or other ac measurement tools, it can be of considerable help in setting and controlling levels through any amplifying chain.
Simple Sine Wave Generator Using 2-Transistor BC550 Circuit

The Simple Sine Wave Generator circuit is based on a simple, two-transistor oscillator circuit, featuring very high frequency and amplitude stability but avoiding thermistors, bulbs or any special amplitude-limiting device. Three different output frequencies, namely: 300Hz, 1KHz and 3KHz, are provided by switching SW1.

The sine wave output amplitude can be varied continuously (by means of P1) in two ranges: 0 - 77.5mV RMS (219.7mV peak-to-peak) and 0 - 0.775V RMS (2.191V peak-to-peak).A regulated supply is necessary to obtain a stable output waveform. D1 and D2 force IC1 to deliver 6.2V output instead of the nominal 5V.

List Componet Of Sine Wave Generator Circuit
P1       : 4K7  Potentiometer
R1 : 12K
R2 : 2K2
R3,R5,R7 : 1K Trimmers
R4,R6 : 1K5
R8 : 1K
R9 : 4K7
R10 : 3K3
R11 : 2K7
R12 : 300R
R13 : 1K (Optional)
R14 : 100K
C1 : 22nF
C2 : 3µ3 Polyester
C3,C6 : 330nF
C4 : 56nF
C5 : 22µF/25V
D1,D2 : 1N4148
D3 : LED
Q1,Q2,Q3 : BC550C
IC1 : 78L05
SW1 : 1 pole 3 ways Rotary or Slider Switch
SW2 : 2 poles 3 ways Rotary or Slider Switch
B1 : 9V PP3 Battery
Detail download here

Simple Signal Injector Using 2 Transistor

This is a signal injector circuit. Signal injector is important tool for troubleshooting your electronic circuits. As an example, this circuit can be used to test amplifier circuit. Here is the schematic diagram of the circuit:
Simple Signal Injector Using 2 Transistor Circuit
This circuit also a lot of harmonics. By connecting the ground clip to the 0v rail and move through each stage, starting at the speaker, the fault in an amplifier can be found. At each preceding stage, the volume will increase. This circuit can inject FM sound sections in TV’s and the IF stages of radios.

When T1 conducts, its collector tension goes from high to low. Via C1, this is transmitted to the base of T2 making its collector tension drop from high to low as well. Via C2, this pulse blocks the base-current of T1, causing it to block up. As soon as the left side of C2 is charged enough by R3, T1 can conduct again and the cyclus is repeated.
Detail download here

12 Volt Transformerless Power Supply

This transformerless power supply circuit will of supply up to about 20mA at 12 volts. It uses capacitive reactance instead of resistance, and it does not generate very much heat.The circuit draws about 30mA AC. If you need more current, use a larger value capacitor, or put two in parallel, but be careful of what you are doing to the Watts. The low voltage 'AC' is supplied by ZD1 and ZD2. The bridge rectifier cans be any of the small 'Round', 'In-line', or 'DIL' types; or Could you use four separate diodes.
12 Volt Transformerless Power Supply Circuit
This power supply can not be modified to Provide currents of greater (can not be up to several amps). The circuit was Designed to Provide a cheap compact power supply for Cmos logic circuits require only A Few That milliamps. The logic circuits were the resource persons then Used to control mains equipment (fans, lights, heaters etc.) through an optically isolated triac. If More Than 20mA is required it is possible to increase of C1 to 0.68uF or 1uF and thus obtain a current of up to about 40mA. But 'suppressor type' capacitors are Relatively big and more expensive Than Regular capacitors; and Increasing the current That means higher wattage resistors and zener diodes are required. If you try to Produce More Than about 40mA the circuit will from no longer be cheap and compact, and it simply makes more sense to use a transformer.

List componet of 12 Volt Transformerless Power Supply
C1             : 470nF/500V
C2 : 100µF/25V
R1 : anything from 1MΩ to 10MΩ
D1, D2, D3, D4 : 1N4007 or rectifier 230V AC
D5 : zenerdiode 12V or matching Uout desired
Detail download here

Simple Lamp Dimmer 220V using Triac

A very simple dimmer circuit with only the essentials. (In this circuit, the values are given for a BT138 at 220V AC, for 115V AC you may have to experiment with the values.)
Simple lamp Dimmer 220V Circuit
  • D1 = diac (silicon bidirectional trigger device) BR100, ER900 or similar
  • Tr1 = triac BT138, TIC226...
  • This circuit is potentially dangerous! this is nothing for beginners!
R1 can vary from one triac to another, put a 220KΩ trimmer in its place and adjust. After adjustment, measure the result and replace the trimmer with an ordinary resistor of the same value.

Circuit From:
Detail download here

3-Digits Digital Volt Meter

This is simple 3-digits digital volt meter. The range is -99mV to +999mV. Two integrated circuits are used, the CA3161 and the CA3162.
3-Digits Digital Volt Meter Circuit
  • The capacitor  must be a low dielectric absorption type such as a polyester or polystyrene type.
  • This capacitor should be placed as close as possible to the power and ground Pins of the CA3161E.
IC1 converts the analogous signal to a digital signal and also produces the multiplex signal to drive T1-T3. The BCD-code from IC1 then goes to IC2, a BCD to 7-segment decoder/driver. From there the signal goes to the displays.

The timing for the CA3162 is supplied by a 786Hz ring oscillator, and the input at pin 6 determines the sampling rate. A 5V input provides a high speed sampling rate (96Hz), and grounding or floating pin 6 provides a low speed (4Hz) sampling rate. When pin 6 is fixed at +1.2V (by placing a 12K resistor between pin 6 and the +5V supply) a 'hold' feature is available. While the CA3162E is in the hold mode, sampling continues at 4Hz but the display data are latched to the last reading prior to the application of the 1.2V. Removal of the 1.2V restores continuous display changes. Note, however, that the sampling rate remains at 4Hz.

The 'EEE' or '---' displays indicate that the range of the system has been exceeded in the positive or negative direction, respectively. Negative voltages to -99mV are displayed with the minus sign in the MSD. The BCD code is 1010 for a negative overrange (---) and 1011 for a positive overrange (EEE).
To callibrate the circuit, connect HIGH and LOW to mass and adjust P1 to read '000'. Then connect a tension from 0 to 1V to HI and LOW with LOW connected to mass. Adjust P2 to read the tension in mV.

The measuring range can be raised, using tension dividers. To use the decimal points, connect DP1, DP2 and/or DP3 to mass.

Circuit From:
Detail download here