STEREO AMPLIFIER

The TDA2822M IC used in this project is a dual amplifier built into an eight pin chip. It consists of two channels, each identical and with external components to provide a very simple but powerful stereo amplifier, with a gain of 39dB and a current draw of 9mA with supply voltage in the range of 1.8 - 15 Volts. It will plug into the earphone socket of Walkman type machines and give excellent quality stereo sound from two speakers. Students are encouraged to research the fascinating technology of speaker box design.

With 55 mm 0.25 Watt Speakers

With 100 mm 2 Watt Speakers

Component	Description	Quantity
Resistor	4R7	2
Variable Resistor	10K	2
Electrolytic Capacitor	0.47uF	2
Electrolytic Capacitor	100uF	2
Electrolytic Capacitor	470uF	2
Electrolytic Capacitor	10uF	1
Ceramic Capacitor	0.1uF	2
IC	TDA 2822	1
IC Socket	8 Pin	1
Speakers	55mm Note: (100mm if requested)	2
Stereo Jack	3mm	1
Figure 8 Wire		1 m
3 Core Wire		0.5 m
Battery Holder	9V	1
PCB Pins		8
Solder		1 m
Slide Switch		1
PCB		1

Component Layout

Construction

1. To make up the Kit, firstly check the PC Board for any damage. Check continuity of all tracks with a multimeter or an electronic circuit tester.
2. The two resistors can be bent to shape and fitted, and the IC socket pushed into place. Solder them but be careful not to bridge across between the legs of the IC socket. The best way to solder is to heat the track beside the leg and apply a touch of solder. When the solder "takes" to the track add more solder and move the soldering iron to touch the leg. Build a small cone of solder making sure you have heated the leg enough for the solder to take.
3. The two 0.1 uF capacitors (104) are not polarised so they can go in any way round. All the other capacitors are electrolytic so you must observe the polarity of each. Look on the body for an arrow pointing down one leg. This leg is the Negative (K) leg of the capacitor. Check the drawing for correct polarity, and push them into place. Bend the legs to stop them from falling out and solder.
4. The two trimpots can be matched to their holes, pushed into place and soldered.
5. Pins are provided to terminate the input and output wires. Their holes are drilled larger. Push them in and solder.
6. Find the small + and - markings on the speaker and solder lengths of Fig.8 wire to them. The wire with the black trace is usually used for the +ve line. The -ve wires from the speakers should be joined and soldered to the circuit board pin in the earth rail of the PCBoard.
7. Connect the 3 Core wire to each of the input pins and ground (common) on the PC Board and the other ends to the two channel terminals of the stereo plug and common.
8. To fix the battery holder in place first melt a dob of solder to each leg up near the plastic, and also beside each of the two holes on the Board, but keep the holes clear. Push the holder into place, right down towards the Board. Use the tip of the soldering iron to fuse the solder together. There is also a switch to be connected across the +ve rail as the drawing shows. Solder both wires to the one side of the switch, centre and one end.
9. You will find that the legs of the IC are spread too wide to fit into the socket. Place the four legs on one side of the IC on the table and push gently so they are bent in slightly. Repeat for the other side. Find the locating DOT on the top surface of the IC, turn it so it is the way the drawing shows and push it into its socket.

Test your amplifier by plugging into the earphone socket of your radio or player, turn the volume down, and switch on. Adjust balance with the trimpots. Mostly you will find that the Amp will work first time.

MORE INFORMATION

View the Datasheet for the TDA 2822.

website:http://cdselectronics.com

LM380 2.5 WATT AMPLIFIER

LM380 2.5 WATT AMPLIFIER

Check Your Kit

• Components

1. Make a visual check of the P.C.Board to ensure no damage has happened in transit. Continuity of the tracks can be checked with a multimeter or an electronic Circuit Tester. Any breaks can be bridged with solder.
2. Turn the Board over, track down, and push the 14 pin I.C. socket into place.
3. Identify the resistors either by their colour bands, or with a multimeter. Bend the legs to match their holes and assemble them. It is a good idea to solder progressively as 4 or 5 components are mounted to the board.
4. The 50K trimpot will fit the three holes in the board D 1.2mm. Push the legs right down.
5. There are five electrolytic capacitors,three 2u2 and two 470uF. On each body you will find an arrow pointing down one leg. This leg is the -ve pole. From the drawing find the + and/or - signs and mount the capacitors in their correct positions. Bend the legs on the back to hold them in place and solder.
6. Six pins are in the Kit. These are soldered into the four 1mm holes where the Input wires and the Speaker wires terminate, and two to connect wires to the ON/OFF switch. Strip the ends of the Fig.8 wire, tin them, and solder to the pins. Usually the wire with the "trace" in the insulation is used for the Positive poles. Find the + and - signs on the speaker and solder in the polarity shown in the diagram. The jack can be connected to the input lead, but join the terminals of the two channels together with a short wire. This is done because the AMP is MONO only and it will amplify both channels into one speaker. Stereo jacks have two small black rings in the shiny shank.
7. Turn the board over ready to mount the battery holder. Build a small amount of solder on the track at the two donuts, but keep the holes clear. Next heat the legs close up to the plastic and build some solder to each leg. Push the battery holder home and touch the tip to the piles of solder. They will fuse easily an hold the battery holder in place.
8. The LM380 I.C. is packed in an antistat case. You will find that the legs are slightly wide to fit the socket. Turn it on its side on a flat surface and gently push down to bend the legs together a little. Repeat for the other side, and offer it into the socket. When it is ready to slide into the socket:

• find the locating DOT on the top of the chip near one end. Make sure the DOT is where the diagram shows.
• use gentle pressure to push it home. I.C. Inserting tools are available. They make the process of pushing the I.C. into the socket much easier.

You are now ready to test your Amplifier. Connect a 9V battery and plug the jack into the output socket of your machine. Adjust the volume of your radio to a comfortable level and use a small screwdriver to adjust the trimpot to get clean undistorted sound from the speaker. Speakers work best in an airtight box made of particle board or similar, and glued together. The hole for the speaker in the front panel of the box should be a neat size to suit the speaker, and can be covered with speaker cloth to give a neat finish. Your Library will likely have information about Speaker Boxes that you can research before you design your box.

MORE INFORMATION

View the Datasheet for the LM380.

TROUBLESHOOTING

If the Amp doesn't work check the following:

• polarity of all five electrolytic capacitors.
• the locating DOT on the LM 380 Chip is as the diagram shows.
• the two resistor values are as the diagram shows.
• carefully prise out the I.C. to check that no legs have been bent up under the body instead of into the socket. Replace it with care.
• remove the battery holder and check all soldering. Re-solder any joints that look suspicious, making sure that the solder takes to the track as well as to the legs.
• remove the end of the jack and check the soldering. Also connect your Amp to another radio to try to isolate the problem.

This is an extremely reliable circuit which presents no real difficulty in putting together, so in most cases the Amp will work first up.

website:http://cdselectronics.com

Automatic Room Lights

An ordinary automatic room power control circuit has only one light sensor. So when a person enters the room it gets one pulse and the lights come ‘on.’ When the person goes out it gets another pulse and the lights go ‘off.’ But what happens when two persons enter the room, one after the other? It gets two pulses and the lights remain in ‘off’ state. The circuit described here overcomes the above-mentioned problem. It has a small memory which enables it to automatically switch ‘on’ and switch ‘off’ the lights in a desired fashion.

The circuit uses two LDRs which are placed one after another (separated by a distance of say half a metre) so that they may separately sense a person going into the room or coming out of the room. Outputs of the two LDR sensors, after processing, are used in conjunction with a bicolour LED in such a fashion that when a person gets into the room it emits green light and when a person goes out of the room it emits red light, and vice versa. These outputs are simultaneously applied to two counters. One of the counters will count as +1, +2, +3 etc when persons are getting into the room and the other will count as -1, -2, -3 etc when persons are getting out of the room. These counters make use of Johnson decade counter CD4017 ICs. The next stage comprises two logic ICs which can combine the outputs of the two counters and determine if there is any person still left in the room or not.

Since in the circuit LDRs have been used, care should be taken to protect them from ambient light. If desired, one may use readily available IR sensor modules to replace the LDRs. The sensors are installed in such a way that when a person enters or leaves the room, he intercepts the light falling on them sequentially—one after the other. When a person enters the room, first he would obstruct the light falling on LDR1, followed by that falling on LDR2. When a person leaves the room it will be the other way round. In the normal case light keeps falling on both the LDRs, and as such their resistance is low (about 5 kilo-ohms). As a result, pin 2 of both timers (IC1 and IC2), which have been configured as monostable flip-flops, are held near the supply voltage (+9V). When the light falling on the LDRs is obstructed, their resistance becomes very high and pin 2 voltages drop to near ground potential, thereby triggering the flip-flops. Capacitors across pin 2 and ground have been added to avoid false triggering due to electrical noise. When a person enters the room, LDR1 is triggered first and it results in triggering of monostable IC1. The short output pulse immediately charges up capacitor C5, forward biasing transistor pair T1-T2. But at this instant the collectors of transistors T1 and T2 are in high impedance state as IC2 pin 3 is at low potential and diode D4 is not conducting. But when the same person passes LDR2, IC2 monostable flip-flop is triggered. Its pin 3 goes high and this potential is coupled to transistor pair T1-T2 via diode D4. As a result transistor pair T1-T2 conducts because capacitor C5 retains the charge for some time as its discharge time is controlled by resistor R5 (and R7 to an extent). Thus green LED portion of bi-colour LED is lit momentarily. The same output is also coupled to IC3 for which it acts as a clock. With entry of each person IC3 output (high state) keeps advancing. At this stage transistor pair T3-T4 cannot conduct because output pin 3 of IC1 is no longer positive as its output pulse duration is quite short and hence transistor collectors are in high impedance state. When persons leave the room, LDR2 is triggered first followed by LDR1. Since the bottom half portion of circuit is identical to top half, this time with the departure of each person red portion of bi-colour LED is lit momentarily and output of IC4 advances in the same fashion as in case of IC3. The outputs of IC3 and those of IC4 (after inversion by inverter gates N1 through N4) are ANDed by AND gates (A1 through A4) are then wire ORed (using diodes D5 through D8). The net effect is that when persons are entering, the output of at least one of the AND gates is high, causing transistor T5 to conduct and energise relay RL1. The bulb connected to the supply via N/O contact of relay RL1 also lights up. When persons are leaving the room, and till all the persons who entered the room have left, the wired OR output continues to remain high, i.e. the bulb continues to remains ‘on,’ until all persons who entered the room have left. The maximum number of persons that this circuit can handle is limited to four since on receipt of fifth clock pulse the counters are reset. The capacity of the circuit can be easily extended for up to nine persons by removing the connection of pin 1 from reset pin (15) and utilising Q1 to Q9 outputs of CD4017 counters. Additional inverters, AND gates and diodes will, however, be required

website :http://www.radiolocman.com

Simple two-transistor circuit lights LEDs

A previous Design Idea describes a circuit that uses an astable multivibrator to drive an LED (Reference). The circuit in Figure 1 uses a simpler alternative approach. The circuit uses a 2N3904 NPN transistor and a 2N3906 PNP transistor, which operate as a high-gain amplifier.



Figure 1. This simple astable multivibrator provides a low-cost way to drive an LED from a single cell.

The 1-MΩ resistor supplies bias current. The 1-kΩ resistor helps linearize the oscillator waveform into one that is close to a square wave with about a 50-to-50 duty cycle. The capacitor supplies positive feedback from the output of the amplifier to the noninverting input. The frequency of oscillation depends mostly on the RC constant of the feedback capacitor and the input-stage impedance. The circuit oscillates at 91 kHz with a 48% duty cycle. You can use almost any common NPN or PNP transistors, as long as they have moderate forward-current gain of 50 or more and can handle 100-mA collector currents.

The LED connects across the output transistor because this approach lets the inductive kickback voltage add to the battery-supply voltage and makes the LED brighter. This circuit operates well from approximately 0.8 to 1.6 V, which is the useful range of an alkaline battery. The LED-light output decreases as the supply voltage decreases from 1.6 to 0.8 V.

Reference

1. Bruno, Luca, “Astable multivibrator lights LED from a single cell,” EDN, Aug 21, 2008, pg 53.

Regulated Dual White LED Lamp

(C) G. Forrest Cook 2008

This project can be used with a CirKits solar circuit kit.

Regulated Dual White LED Lamp

Introduction

This is an ultra-simple LED lamp made with two white LEDs. It is suitable for use in both 12V solar powered and automotive applications. Only seven components are used in this circuit. It produces regulated light output from 11V to 20V. The circuit board can be potted in silicone to make the lamp completely water proof.

Specifications

Nominal Operating Voltage: 12V DC Regulated Light Voltage Range:

11-20V Operating Current: 20ma 

Theory

The input power is filtered through a pi filter consisting of two 100nF capacitors and a 100 ohm resistor, this removes voltage spikes from the rest of the circuitry. The LM317L and 56 ohm resistor act as a current regulator that is set to 20ma. The current regulator is wired in series between the power source and the LEDs to provide a constant current.

Construction

A small circuit board was made using press-n-peel blue film, the board was sized to fit inside of a 1/2" PVC pipe connector. The parts were soldered into the circuit board and a length of two conductor speaker wire was soldered to the board for the power lead. A knot was tied in the power cable to act as a strain relief. The power cable was fed through a hole in the PVC connector. The entire assembly was filled with clear GE Silicone II caulk and left to dry. Be sure to allow the caulk to dry for several days in a warm place before applying power. Another brand of bathtub caulk was tried, but the caulk was electrically conductive and the circuit quickly failed.

Use

Connect this circuit to a 12V battery or power supply, be sure to observe the correct polarity. The LEDs should put out a bright white light. This light can be used for a night light, a flash light, automotive interior lights and background house lighting. The low current draw allows it to run for many hours on a battery.

Parts

2x white LEDs, T1-3/4 size 1x 56 ohm 1/4 W resistor 1x 100 ohm 1/4 W resistor

2x 0.1uF capacitors 1x LM317L adjustable voltage regulator 1x 1/2" Schedule 40 PVC

 pipe junction GE Silicone II caulk Two conductor speaker wire

CAD Files
EAGLE CAD schematic  
EAGLE CAD board layout  
PostScript file of PC Board

website : http://www.solorb.com/

Knightrider lights for model cars Circuit

This simple circuit drives 6 LEDs in 'Knightrider scanner mode'. Power consumption depends mainly on the type of LEDs used if you use a 7555 (555 CMOS version).

Circuit diagram

Note that VDD and GND for the ICs are not shown in the circuit drawing.

Pin-outs:
(7)555
1 GND
2 TRIGGER
3 OUTPUT
4 RESET
5 CONTROL VOLTAGE
6 THRESHOLD
7 DISCHARGE
8 VDD

4017
1 Q5
2 Q1
3 Q0
4 Q2
5 Q6
6 Q7
7 Q3
8 GND
9 Q8
10 Q4
11 Q9
12 CO
13 NOT ENABLE
14 CLK
15 RESET
16 VDD

author:Oscar den Uijl, odu@xs4all.nl
website: http://www.xs4all.nl/~odu/

Black Light Circuit

This circuit is a simple ultraviolate light that can be powered by a 6 volt battery or power supply that is capable of supplying 1 or more amps.

Circuit diagram

Parts
C1 0.0047uf Mono Capacitor
C2 0.1uf Disc Capacitor
D1, D2 1N4007 Diode
FTB Filtered Blacklight Tube
IC1 555 Timer IC
P1 10k Trim Pot
Q1 TIP30 PNP Power Transistor
R1 470 Ohm Resistor
R2 270 Ohm Resistor
T1 Medium Yellow Inverter Transformer
MISC IC Socket, Heat Sink For Q1, Screw, Nut, Wire and PC Board

Notes:
1. P1 changes brightness of the black light tube.

Author:

Fading LEDs Circuit

Two strips of LEDs fading in a complementary manner

9V Battery-operated portable unit

Circuit diagram

Parts:
R1,R2 4K7 1/4W Resistors
R3 22K 1/4W Resistor
R4 1M 1/4W Resistor (See Notes)
R5 2M2 1/4W Carbon Trimmer (See Notes)
R6,R10,R11,R14,R15 10K 1/4W Resistors
R7,R8 47K 1/4W Carbon Trimmers (See Notes)
R9,R13 27K 1/4W Resistors
R12,R16 56R 1/4W Resistors
C1 1?F 63V Polyester Capacitor
C2 100?F 25V Electrolytic Capacitor
D1-D4 etc 5 or 3mm. LEDs (any type and color) (See Notes)
IC1 LM358 Low Power Dual Op-amp
Q1,Q2,Q4 BC327 45V 800mA PNP Transistors
Q3,Q5,Q6 BC337 45V 800mA NPN Transistors
SW1 SPST miniature Slider Switch
B1 9V PP3 Battery
Clip for PP3 Battery

Device purpose:
This circuit operates two LED strips in pulsing mode, i.e. one LED strip goes from off state, lights up gradually, then dims gradually, etc. while the other LED strip do the contrary.
Each strip can be made up from 2 to 5 LEDs at 9V supply.

Circuit operation:
The two Op-Amps contained into IC1 form a triangular wave generator. The rising and falling voltage obtained at pin #7 of IC1 drives two complementary circuits formed by a 10mA constant current source (Q1, Q2 and Q5, Q6) and driver transistor (Q3 and Q6).
R4, R5 & C1 are the timing components: the total period can be varied changing their values. R7 & R8 vary the LEDs brightness.

Notes:
For those whishing to avoid the use of trimmers, suggested values for a 9V supply are:
R4=3M9, R9 & R13=47K and trimmers replaced by a short.
Whishing to use a wall-plug transformer-supply instead of a 9V battery, you can supply the circuit at 12V, allowing the use of up to 6 LEDs per strip, or at 15V, allowing the use of up to 7 LEDs per strip.
In this case, the value of the trimmers R7 & R8 should be changed to 100K.

author:RED Free Circuit Designs,
website: http://www.redcircuits.com

8 Random Flashing Leds Circuit

This project flashes eight LEDs in an apparently random manner. It uses a 4060 combined counter and display driver IC which is designed for driving 7-segment LED displays. The sequence is not really random because seven of the LEDs would normally be the display segments, the eighth LED is driven by an output that is normally used for driving further counters. The table below shows the sequence for the LEDs. You can use less than eight LEDs if you wish and the table may help you decide which ones to use for your purpose.

Dancing LEDs Circuit

A LED sequencer, following the rhythm of music or speech

9V Battery-operated portable unit

Circuit diagram

Parts:
R1 10K 1/4W Resistor
R2,R3 47K 1/4W Resistors
R4 1K 1/4W Resistor
R5,R6,R7 100K 1/4W Resistors
R8 820R 1/4W Resistor
C1,C3 100nF 63V Ceramic or Polyester Capacitors
C2 10?F 50V Electrolytic Capacitor
C4 330nF 63V Polyester Capacitor (See Notes)
C5 100?F 25V Electrolytic Capacitor
D1 1N4148 75V 150mA Diode
D2-D11 5 or 3mm. LEDs (any type and color)
IC1 LM358 Low Power Dual Op-amp
IC2 4017 Decade counter with 10 decoded outputs IC
M1 Miniature electret microphone
SW1 SPST miniature Slider Switch
B1 9V PP3 Battery
Clip for PP3 Battery
Additional circuit parts (see Notes):
R9,R10 10K 1/4W Resistors
R11 56R 1/4W Resistor
D12,D13 etc 5 or 3mm. LEDs (any type and color)
Q1,Q2 BC327 45V 800mA PNP Transistors
Q3 BC337 45V 800mA NPN Transistor

Device purpose:
The basic circuit illuminates up to ten LEDs in sequence, following the rhythm of music or speech picked-up by a small microphone. The expanded version can drive up to ten strips, formed by up to five LEDs each, at 9V supply.

Circuit operation:
IC1A amplifies about 100 times the audio signal picked-up by the microphone and drives IC1B acting as peak-voltage detector. Its output peaks are synchronous with the peaks of the input signal and clock IC2, a ring decade counter capable of driving up to ten LEDs in sequence.
An additional circuit allows the driving of up to ten strips, made up by five LEDs each (max.), at 9V supply. It is formed by a 10mA constant current source (Q1 & Q2) common to all LED strips and by a switching transistor (Q3), driving a strip obtained from 2 to 5 series-connected LEDs. Therefore one transistor and its Base resistor are required to drive each strip used.

Notes:
The sensitivity of the circuit can be varied changing R4 value.
C4 value can be varied from 220 to 470nF in order to change the circuit speed-response to music peaks.
Adopting the additional circuit, only one item for R10, R11, Q1 and Q2 is required to drive up to ten LED strips. On the contrary, one item of R9 and Q3 is necessary to drive each strip you decided to use.
Each R9 input must be connected to IC2 output pins, in place of the LEDs D2-D11 shown. R8 must also be omitted.
Whishing to use a lower number of LEDs or LED strips, pin #15 of IC2 must be disconnected from ground and connected to the first unused output pin. Example:
if you decided t use 5 LEDs, pin #15 of IC2 must be connected to pin #1; if you decided to use 8 LEDs, pin #15 of IC2 must be connected to pin #9 etc.
Current drawing of the circuit is about 10mA.
Whishing to use a wall-plug transformer-supply instead of a 9V battery, you can supply the circuit at 12V, allowing the use of up to 6 LEDs per strip, or at 15V, allowing the use of up to 7 LEDs per strip.

author:RED Free Circuit Designs,
website: http://www.redcircuits.com/