Simple LM386 Audio Amplifier

This simple amplifier shows the LM386 in a high-gain configuration (A = 200). For a maximum gain of only 20, leave out the 10 uF connected from pin 1 to pin 8. Maximum gains between 20 and 200 may be realized by adding a selected resistor in series with the same 10 uF capacitor.


The 10k potentiometer will give the amplifier a variable gain from zero up to the maximum.

This circuit can be used to strengthen  signals from the mini radio,  music bell, and other children toys.

Sumber : http://www.rangkaian-elektronika.com/

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Rangkaian Lampu Darurat Otomatis

Apabila listrik di rumah kita mengalami pemadaman, terutama di malam hari maka kita akan merasa kesulitan untuk segera menerangi rumah kita dengan lampu /senter atau lampu minyak karena suasana yang gelap dengan tiba-tiba akan membuat kita bingung dimana kita menaruh senter, lampu minyak bahkan dimana kita menaruh korek api.
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Unit ini bekerja untuk “mengisi” baterai nikel-cadmium dari tegangan jala-jala, sehingga didapatkan catu daya yang siap pakai untuk penerangan darurat selama terjadi pemadaman listrik. Pada saat terjadi pemadaman, penerangan darutat akan hidup secara otomatis.
Rangkaian untuk unit ini sangat sederhana. Komponen-komponen Tr1, D1, dan C1, memberikan penyearahan setengah gelombang dan catu daya DC yang rata pada 6V. Melalui R1 dan D2, baterai Ni-Cad diisi secara kontinyu dengan arus sekitar 100mA. Dengan kondisi arus dan tegangan seperti ini, sebuah baterai Ni-Cad 2Ah dapat diisi dengan aman.
Tegangan jatuh pada D2 memberikan panjaran terbalik pada pertemuan basis emitor T1, sehingga transistor ini tidak bekerja dan lampu-lampu padam. Bila tegangan jala-jala padam, T1 dicatu dengan arus basis melalui R2. Transistor kemudian bekerja dan lampu-lampu akan menyala. Bila kemudian tegangan jala-jala masuk, T1 tidak akan bekerja, lampu-lampu padam, dan baterai kembali diisi melalui R1 dan D2.
Unit ini dapat diletakkan di tempat manapun yang memerlukan penerangan darurat bila listrik tiba-tiba padam. Satu contoh yang nyata adalah kotak sekering putus dapat dilakukan penggantian dengan cepat dan mudah.
Dapat juga digunakan sebuah tranformator dengan tegangan sekunder yang sedikit lebih tinggi, asalkan R1 juga dinaikan nilainya sehingga membatasi arus yang melalui resistor ini tidak lebih dari 100mA.


Sumber: iooi+rangkaian+elktr.bmp
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LED 12 Volt Lead Acid Battery Meter

In the circuit below, a quad voltage comparator (LM339) is used as a simple bar graph meter to indicate the charge condition of a 12 volt, lead acid battery. A 5 volt reference voltage is connected to each of the (+) inputs of the four comparators and the (-) inputs are connected to successive points along a voltage divider. The LEDs will illuminate when the voltage at the negative (-) input exceeds the reference voltage. Calibration can be done by adjusting the 2K potentiometer so that all four LEDs illuminate when the battery voltage is 12.7 volts, indicating full charge with no load on the battery. At 11.7 volts, the LEDs should be off indicating a dead battery. Each LED represents an approximate 25% change in charge condition or 300 millivolts, so that 3 LEDs indicate 75%, 2 LEDs indicate 50%, etc. The actual voltages will depend on temperature conditions and battery type, wet cell, gel cell etc. Additional information on battery maintenance can be found at:
Battery Maintenance Tutorial


Sumber :  http://www.bowdenshobbycircuits.info/page11.htm#counter.gif

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A Bedside Lamp Timer Circuit Schematic

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The purpose of this circuit is to power a lamp or other appliance for a given time (30 minutes in this case), and then to turn it off. It is useful when reading at bed by night, turning off the bedside lamp automatically in case the reader falls asleep... After turn-on by P1 pushbutton, the LED illuminates for around 25 minutes, but then it starts to blink for two minutes, stops blinking for two minutes and blinks for another two just before switching the lamp off, thus signaling that the on-time is ending. If the user want to prolong the reading, he/she can earn another half-hour of light by pushing on P1. Turning-off the lamp at user's ease is obtained by pushing on P2.<span class="fullpost">

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Circuit diagram:

A Bedside Lamp Timer Circuit Diagram

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Parts:

Resistors
R1 = 1K
R2 = 4K7
R3 = 10M
R4 = 1M
R5 = 10K

Capacitors
C1 = 470µF-25V
C2-C4100nF-63V

Semiconductors
C1 = 470µF-25V
C2-C4 = 100nF-63V
D1-D4 = 1N4002
D5 = 5mm. Red LED
IC1 = CD4012
IC2 = CD4060
Q1 = BC328
Q2 = BC547

Miscellaneous
P1,P2 = SPST Pushbuttons
T1 = 9+9 Volt Secondary 1VA Mains transformer
RL1 = 10.5V 470 Ohm Relay with SPDT 2A 220V switch
PL1 = Male Mains plug
SK1 = Female Mains socket

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Circuit operation:

Q1 and Q2 form an ALL-ON ALL-OFF circuit that in the off state draws no significant current. P1 starts the circuit, the relay is turned on and the two ICs are powered. The lamp is powered by the relay switch, and IC2 is reset with a positive voltage at pin 12. IC2 starts oscillating at a frequency set by R4 and C4. With the values shown, pin 3 goes high after around 30 minutes, turning off the circuit via C3. During the c6 minutes preceding turn-off.

The LED does a blinking action by connections of IC1 to pins 1, 2 & 15 of IC2. Blinking frequency is provided by IC2 oscillator at pin 9. The two gates of IC1 are wired in parallel to source more current. If required, a piezo sounder can be connected to pins 1 & 14 of IC1. Obviously, timings can be varied changing C4 and/or R4 values.


Sumber :  http://www.extremecircuits.net/2009/12/bedside-lamp-timer-circuit-schematic.html
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Simple Morse Practice Oscillator Circuit

This will be my next homebrew project, a morse practice oscillator circuit. 9W2AZV and I are going to build this as we are preparing ourselves to perfect our Morse code sending/receiving skills.
In the spirit of amateur radio/ham, we will homewbrew the equipment using easily obtainable parts from our nearest electronic stores.
Here’s the circuit

We are still thinking of the easiest and cheapest way to homebrew the keyer, but we are considering to use discarded/faulty computer mouse as our first keyer.

As a bonus, we thought of hooking this keyer straight to PC serial port, so we could use it with XChat CWirc plugin to enable us to test our Morse skill on the irc.
With the amount of work i’m having this week, I would estimate that this project would be completed by the end of March. So stay tune for photos!

Sumber :   http://please.name.my/127/simple-morse-practice-oscillator-circuit.html Read More..

Rangkaian Sensor Suhu

Rangkaian sensor suhu ini  sangat mirip dengan rangkaian sensor yang lain. Pada dasarnya perbedaan hanya terletak pada bagaimana kita memanfaatkan perubahan kondisi dari suatu komponen sensor menjadi sinyal listrik. Untuk beberapa contoh rangkaian sensor yang sederhana anda bisa menggunakan prinsip pembagian tegangan antara variable resistor dan komponen yang dipasang seri dengan menggunakan satu atau dua buah transistor. Tetapi untuk mendapatkan hasil yang lebih memuaskan anda bisa menggunakan IC Op-Amp agar bisa menghitung secara mudah nilai penguatan yang diinginkan.

Pada rangkaian ini juga  tetap memanfaatkan fungsi monostable dari IC 555 sebagai penahan aktif rangkaian alarm selama waktu yang ditentukan. Jika anda tidak ingin menahan kondisi output sensor pada saat terjadinya sinyal trigger dari rangkaian sensor maka anda tidak perlu menggunakan IC 555 beserta rangkaian monostable-nya.

Gambar rangkaian sensor suhu | Skema rangkaian sensor suhu

Daftar Komponen :

1. Resistor : R1 (100 Kohm), R2 (10 Kohm), R3 (47 Kohm), R4 (1 Kohm) dan VR1 (potensio 10 Kohm)

2. Kapasitor : C1 (10 uF) dan C2 (1 uF)

3. Dioda : D1 (IN 4002)

4. Transistor : Q1 (BC 107)

5. Thermistor

6. IC 555

7. Relay 9 volt

8. Rangkaian alarm (sesuai selera)

Prinsip Kerja dan Analisa Rangkaian :

1. R3, Thermistor dan VR1 dipasang seri supaya dapat menentukan pembagian tegangan yang sesuai yang akan diberikan ke transistor switching.
2. Tegangan supply adalah sama dengan jumlah tegangan yang jatuh pada R3, Thermistor dan VR1. Tegangan pada VR1 paralel terhadap basis transistor, sehingga pada saat tegangan pada VR1 mencapai 0,7 volt maka transistor akan aktif dan men-trigger rangkaian monostable.
3. Thermistor dipasang pada bagian atas dari VR1 dimaksudkan supaya pada saat suhu naik tegangan pada titik trigger (basis transistor = VR1) akan mengalami kenaikan, dikarenakan thermistor (NTC) tersebut akan mengalami penurunan nilai resistansi seiring dengan kenaikan suhu.
4. Anda bisa saja menukar posisi thermistor dengan VR1 dengan tujuan agar rangkaian alarm akan aktif pada saat suhu mengalami penurunan.
5. Anda bisa juga meengganti nilai R3 dan VR1 untuk mendapatkan sensitifitas yang sesuai dengan karakteristik thermistor yang anda miliki dan sesuai keinginan anda.

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Alarm Circuit

Cara Kerja 
Sirkuit akan  mendeteksi bayangan yang tiba-tiba jatuh di sensor cahaya dan suara akan dibangkitkan sebagai indikator gerakan melalui sebuah  speaker kecil. Sirkuit ini  tidak akan merespon perubahan cahaya yanga bertahap dalam kecerahan untuk mencegah alarm palsu. Cahaya normal  dapat digunakan, tetapi rangkaian akan bekerja jika seberkas cahaya diatur jatuh pada sensor cahaya. Sensor cahaya adalah LDR (Resistor tergantung cahaya) . Komponen ini memiliki nilai tahanan  yang rendah dalam cahaya terang ringan dan mempunyai nilai tahanan yang tinggi dalam cahaya gelap atau redup. Kepekaan rangkaian ini dapat diatur sesuai dengan keinginan dengan menggunakan sebuah pengatur trimpot. Read More..

Rangkaian UPS Mini

UPS (Uninterruptible Power Supply), digunakan untuk mengantisipasi listrik padam. Walau tidak sehandal UPS yang asli, rangkaian ini sedikit bermakna, Mau tau cara merakitnnya...?

Gampang dan mudah. Biayanya pun relatif lebih murah ketimbang membeli UPS yang asli. Bagaimana dengan komponen yang diperlukan ? Banyak terjual di toko-toko elektronik. Dengan demikian anda akan merugi jika tidak mencoba merakitnya.

Output rangkaian UPS ini memiliki daya sekitar 1,5W. Sebelum rangkaian utama terdapat rangkaian layaknya mini adapter yang memiliki tegangan antara 9V/12V dengan kuat arus sebesar 500mA. Tegangan yang dihasilkan ini digunakan untuk mengoperasikan rangkaian dan mengisi battery. UPS dirancang untuk tetap dapat menjalankan perangkat elektronik meskipun listrik padam.

Cara Kerja Rangkaian

Ketika inverter dijalankan dengan masukan AC, kemudian di ubah menjadi tegangan DC. Pada bagian output penyearah digunakan untuk mengisi battery. Ketika power gagal atau terjadi pemadaman arus listrik, tegangan dc mengalir ke inverter yang kemudian menghasilkan tegangan AC pada keluaran inverter (lebih jelasnya lihat gambar).

rangkaian terhubung disekitar IC CD4047 yang beroperasi sebagai multivibrator pada frekuensi 50 Hz. Output Q multivibrator ini menggerakkan MOSFETs IRF540. Outout inverter disaring dan direduksi menggunakan MOV (Metal Oxide Vasitor). Tranformer yang digunakan adalah 9-0-9, 1.5A. Dua LED (D6 dan D7) digunakan sebagai indikator apakah tegangan utama ataukah baattery yang sedang bekerja. Read More..

Pengusir Tikus Elektronik

Dafar Komponen
R1	: 1K8
R2	: 1K
R3	: 5K6
R4	: 480R
C1	: 2,2nF
C2	: 0,022uF/6V
IC	: 555
Q	: SC1162
Speaker 4 ohm

 Rangkaian elektronik seperti pada gambar di atas dapat digunakan untuk mengusir gangguan tikus.Dengan rangkaian ini kita tidak perlu repot-repot menghalau ataupun membunuh mereka dengan bermacam-macam jenis racun yang kadang -kadang justru malah merepotkan kita. . Dengan frekuensi 50Khz yang dihasilkan
oleh rangkaian tersebut dijamin tikus-tikus akan berlarian perkarena telinganya
akan merasa sakit akibat getaran signal frekuensi tersebut. Read More..

Time Delay Circuit

In the design of analog circuits, there are times when you would need to delay a pulse that came into a circuit before being used for the next process. This time delay circuit uses a 555 timer to delay a pulse that comes in to a maximum time of 75 seconds. The timing of the delay can also be changed by changing the resistor value of VR1 and the capacitor value of E based on the time delay formula of t=0.69RC.

In order for the output to go high, the reset pin of 555 timer (pin 4) must be high and the TRIGGER pin (pin 2) voltage level must be below a third of the level of the power supply to the IC. When there is no pulse being applied to the input, transistor Q1 will turn ON and capacitor E is charged.

IC 555 Time Delay Relay Circuit

Once a pulse is applied to the input, transistor Q1 will turn OFF and pin 4 reset pin is held to high. This caused the capacitor E1 to be discharged through VR1 resistor. The time delay will depend on the discharged of capacitor E to a third of the supply before the output of 555 goes high. Experiment with different values of VR1 and E to get different time delay.

If the maximum value of potentiometer is set to 5M ohm, the time delay of the pulse will be 75 seconds.

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Light Dark Sensor With Relay Circuit Using LM741

Below is a schematic diagram of an LM741 light/dark sensor circuit (from the excellent 741 Op-Amp Tutorial by Tony van Roon).

The ECG128/NTE128 transistor stipulated can be substituted with any NPN transistor rated at sufficient gain and current for the chosen relay coil.

1st Nov 2007 Update - We have modified the schematic diagram above with the addition of a 220uF smoothing capacitor between the base of transistor Q1 and ground. Without this capacitor, the relay chatter (relay switching on and off many times per second) was terrible around the switch on/off light level. By adding the capacitor, relay chatter was completely eliminated.

According to the designer of this circuit, the relay will be closed only when "NO light falls on LDR1", however, in testing this circuit proved to work very well with the user able to adjust the potentiometer (P1) to automatically close the relay at whatever light level they chose.

By swapping the postitions of the 10K resistor (R1) and the LDR (LDR1), the relay will be closed when the LDR is under light rather than under darkness. Therefore a device can automatically be switched off at nighttime.

Since this circuit still contains a relay we need to make some changes* to reduce the amount of power to make it more suitable for renewable energy powered low-current applications.

 

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Photo Electric Street Light

This is basically a Schmitt Trigger circuit which receives input from a cadmium sulfide photo cell and controls a relay that can be used to switch off and on a street lamp at dawn and dusk. I have built the circuit with a 120 ohm/12 volt relay and monitored performance using a lamp dimmer, but did not connect the relay to an outside light.
The photo cell should be shielded from the lamp to prevent feedback and is usually mounted above the light on top of a reflector and pointed upward at the sky so the lamp light does not strike the photo cell and switch off the lamp.
The photo cell is wired in series with a potentiometer so the voltage at the junction (and base of transistor) can be adjusted to about half the supply, at the desired ambient light level. The two PNP transistors are connected with a common emitter resistor for positive feedback so as one transistor turns on, the other will turn off, and visa versa. Under dark conditions, the photo cell resistance will be higher than the potentiometer producing a voltage at Q1 that is higher than the base voltage at Q2 which causes Q2 to conduct and activate the relay.
The switching points are about 8 volts and 4 volts using the resistor values shown but could be brought closer together by using a lower value for the 7.5K resistor. 3.3K would move the levels to about 3.5 and 5.5 for a range of 2 volts instead of 4 so the relay turns on and off closer to the same ambient light level. The potentiometer would need to be readjusted so that the voltage is around 4.5 at the desired ambient condition. Read More..

LED Traffic Lights

The LED traffic Light circuit controls 6 LEDs (red, yellow and green) for both north/south directions and east/west directions. The timing sequence is generated using a CMOS 4017 decade counter and a 555 timer. Counter outputs 1 through 4 are wire ORed using 4 diodes so that the (Red - North/South) and (Green - East/West) LEDs will be on during the first four counts. The fifth count (pin 10) illuminates (Yellow - East/West) and (Red - North/South). Counts 6 through 9 are also wire ORed using diodes to control (Red - East/West) and (Green - North/South). Count 10 (pin 11) controls (Red - East/West) and (Yellow - North/South). The time period for the red and green lamps will be 4 times longer than for the yellow and the complete cycle time can be adjusted with the 47K resistor. The eight 1N914 diodes could be subsituted with a dual 4 input OR gate (CD4072). Read More..

Line Powered White LEDs

The LED circuit below is an example of using 25 white LEDs in series connected to the 120VAC line. It can be modified for more or less LEDs by adjusting the resistor value. The exact resistance will depend on the particular LEDs used. But working out the resistor value is a bit complicated since current will not continously flow through the resistor.
In operation, the output of the bridge rectifier will be about 120 DC RMS or 170 volts peak. If we use 25 white LEDs with a forward voltage of 3 volts each, the total LED voltage will be 75 volts. The peak resistor voltage will be 170- 75 or 95 volts but the resistor voltage will not be continous since the input must rise above 75 before any current flows. This (dead time) represents about 26 degrees of the 90 degree half wave rectified cycle, (asin) 75/170 = (asin) .44 = 26 degrees. This means the resistor will conduct during 90-26 = 64 degrees, or about 71 percent of the time.
Next we can work out the peak LED current to determine the resistor value. If the LED current is 20mA RMS, the peak current will be 20*1.414 or 28mA. But since the duty cycle is only 71 percent, we need to adjust this figure up to 28/0.71 = 39mA. So, the resistor value should be 95/.039 = 2436 ohms (2.4K) and the power rating will be .02^2 *2400= .96 watts. A two watt size is recommended.
Now this circuit can also be built using 2 diodes and resistor as shown in the lower drawing. The second diode in parallel with the LEDs is used to avoid a reverse voltage on the LEDs in case the other diode leaks a little bit. It may not be necessary but I thought it was a good idea.
Working out the resistor value is similar to the other example and comes out to about half the value of the full wave version, or about 1.2K at 1 watt in this case. But the peak LED current will be twice as much or about 78mA. This is probably not too much, but you may want to look up the maximum current for short duty cycles for the LEDs used and insure 79mA doesn't exceed the spec. Read More..

AC Line powered LEDs

The circuit below illustrates powering a LED (or two) from the 120 volt AC line using a capacitor to drop the voltage and a small resistor to limit the inrush current. Since the capacitor must pass current in both directions, a small diode is connected in parallel with the LED to provide a path for the negative half cycle and also to limit the reverse voltage across the LED. A second LED with the polarity reversed may be subsituted for the diode, or a tri-color LED could be used which would appear orange with alternating current. The circuit is fairly efficient and draws only about a half watt from the line. The resistor value (1K / half watt) was chosen to limit the worst case inrush current to about 150 mA which will drop to less than 30 mA in a millisecond as the capacitor charges. This appears to be a safe value, I have switched the circuit on and off many times without damage to the LED. The 0.47 uF capacitor has a reactance of 5600 ohms at 60 cycles so the LED current is about 20 mA half wave, or 10 mA average. A larger capacitor will increase the current and a smaller one will reduce it. The capacitor must be a non-polarized type with a voltage rating of 200 volts or more.
The lower circuit is an example of obtaining a low regulated voltage from the AC line. The zener diode serves as a regulator and also provides a path for the negative half cycle current when it conducts in the forward direction. In this example the output voltage is about 5 volts and will provide over 30 milliamps with about 300 millivolts of ripple. Use caution when operating any circuits connected directly to the AC line.

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1.5 Volt LED Flashers

The LED flasher circuits below operate on a single 1.5 volt battery. The circuit on the upper right uses the popular LM3909 LED flasher IC and requires only a timing capacitor and LED.
The top left circuit, designed by Andre De-Guerin illustrates using a 100uF capacitor to double the battery voltage to obtain 3 volts for the LED. Two sections of a 74HC04 hex inverter are used as a squarewave oscillator that establishes the flash rate while a third section is used as a buffer that charges the capacitor in series with a 470 ohm resistor while the buffer output is at +1.5 volts. When the buffer output switches to ground (zero volts) the charged capacitor is placed in series with the LED and the battery which supplies enough voltage to illuminate the LED. The LED current is approximately 3 mA, so a high brightness LED is recommended.
In the other two circuits, the same voltage doubling principle is used with the addition of a transistor to allow the capacitor to discharge faster and supply a greater current (about 40 mA peak). A larger capacitor (1000uF) in series with a 33 ohm resistor would increase the flash duration to about 50mS. The discrete 3 transistor circuit at the lower right would need a resistor (about 5K) in series with the 1uF capacitor to widen the pulse width.

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Generating -5 Volts From a 9 Volt Battery

A 555 timer can be used to generate a squarewave to produce a negative voltage relative to the negative battery terminal. When the timer output at pin 3 goes positive, the series 22 uF capacitor charges through the diode (D1) to about 8 volts. When the output switches to ground, the 22 uF cap discharges through the second diode (D2) and charges the 100 uF capacitor to a negative voltage. The negative voltage can rise over several cycles to about -7 volts but is limited by the 5.1 volt zener diode which serves as a regulator. Circuit draws about 6 milliamps from the battery without the zener diode connected and about 18 milliamps connected. Output current available for the load is about 12 milliamps. An additional 5.1 volt zener and 330 ohm resistor could be used to regulate the +9 down to +5 at 12 mA if a symmetrical +/- 5 volt supply is needed. The battery drain would then be around 30 mA.

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555 Tone Generator (8 ohm speaker)

This is a basic 555 squarewave oscillator used to produce a 1 Khz tone from an 8 ohm speaker. In the circuit on the left, the speaker is isolated from the oscillator by the NPN medium power transistor which also provides more current than can be obtained directly from the 555 (limit = 200 mA). A small capacitor is used at the transistor base to slow the switching times which reduces the inductive voltage produced by the speaker. Frequency is about 1.44/(R1 + 2*R2)C where R1 (1K) is much smaller than R2 (6.2K) to produce a near squarewave. Lower frequencies can be obtained by increasing the 6.2K value, higher frequencies will probably require a smaller capacitor as R1 cannot be reduced much below 1K. Lower volume levels can be obtained by adding a small resistor in series with the speaker (10-100 ohms). In the circuit on the right, the speaker is directly driven from the 555 timer output. The series capacitor (100 uF) increases the output by supplying an AC current to the speaker and driving it in both directions rather than just a pulsating DC current which would be the case without the capacitor. The 51 ohm resistor limits the current to less than 200 mA to prevent overloading the timer output at 9 volts. At 4.5 volts, a smaller resistor can be used.

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