Multi Switch Doorbell With Indicators Circuit Diagram

Description

Here’s the circuit of a multi-switch input musical doorbell (shown in Fig.1). The circuit is built around the popular and less expensive quad D-latch CD4042B (IC1).
When switch S6 is pushed to ‘on’ condition, the circuit gets +9V and the four data inputs (D1 through D4) of ICI are in low state because these are tied to ground via resistors R1 through R4. Polarity input (POL) pin 6 of IC1 is also pulled down by resistor R5.

Circuit Diagram

Clock input (pin 5) of the quad D-latch is wired in normally low mode and hence all the four outputs (Q0 through Q3) have the same states as their corresponding data inputs. As a result, LED1 through LED4 are in off condition.
There are four switches fitted at four different doors/gates outside the home and a monitoring panel (as shown in Fig. 2) in the common room of the home. If any switch is pressed by a visitor (for example switch S1 at door 1), pins 2 and 4 of IC1 go high.
Simultaneously, pin 3 to IC1 (Q0 output) goes low and LED1 starts glowing to indicate that switch S1 is pressed by someone.
Next, output pin 13 of the dual 4-input NOR gate (IC2, here wired as a single 4-input OR gate) goes high to forward bias buzzerdriver transistor T1 via resistor R10.
The final result is a soft and pleasing musical bell, which lasts until reset switch S5 is pressedby the owner. For this latching arrangement, output pin 13 of IC2 from the NOR gate is fed back tothe clock input of IC1. The circuit costs around Rs 100.

Author T.K. HAREENDRAN

Source-http://www.atombus.biz/2012/02/multi-switch-doorbell-with-indicators.html

07:28 0 comments

USB Charger Circuit Diagram

Description

This is a portable battery powered USB charger circuit. This circuit is able to charge your PDAs, Ipods, Mp3 players and any device that plug in to a computer USB to charge. If you fit this circuit in a small box with a 9V battery then it will become a portable emergency USB charger.

The schematic is so simple using only few components so you can make this circuit in some minutes if all parts available with you. The circuit is using low dropout regulator IC LM7805 which is easily available in the market and it is also very cheap. The circuit takes voltage from 9V battery and step down the voltage in to a DC 5V output.

 Circuit Diagram

 Source- http://circuitdiagram.org/usb-charger.html

08:12 0 comments

Intruder Alarm Circuit Diagram

Circuit Diagram

Description

This is a circuit which sounds on the momentary breaking up of a guard circuit comprising a magnet and a reed switch a small permanent magnet is fitted at the edge of the door to be guarded, a normally open reed switch is fitted on the door frame or a wall facing the magnet.
In the normally closed condition of the door, the reed switch is very close to the magnet and hence the reed contact is kept closed. When the door is opened the reed switch contact opens. This triggers a scr, the gate of the scr is connected to its cathode through the reed switch. As long as the switch is closed, the scr dose not fire, but when the door is opened the switch also opens and the scr fires, supplying voltage to the alarm.

Engineers note:

This alarm looks so simple but it is more effective and fool proof the audio signals can further be amplified according to the area or the place it is fixed and the major plus point is that even if the door is closed after opening or in case if the door is opened an closed immediately the alarm keeps on blowing continuously. Constructional details are also added along with this article for better understanding.

Constructional Details:

 Source -http://www.electronguide.com/circuits_pages/IntruderAlarm.html

07:14 4 comments

Amplified Ear Circuit Diagram

Description 

 This circuit, connected to 32 Ohm impedance mini-earphones, can detect very remote sounds. Useful for theatre, cinema and lecture goers: every word will be clearly heard. You can also listen to your television set at a very low volume, avoiding to bother relatives and neighbors. Even if you have a faultless hearing, you may discover unexpected sounds using this device: a remote bird twittering will seem very close to you.

Circuit Diagram:

Parts:

• P1 = 22K
• R1 = 10K
• R2 = 1M
• R3 = 4K7
• R4 = 100K
• R5 = 3K9
• R6 = 1K5
• R7 = 100K
• R8 = 100R
• R9 = 10K
• C1 = 100nF 63V
• C2 = 100nF 63V
• C3 = 1µF 63V
• C4 = 10µF 25V
• C5 = 470µF 25V
• C6 = 1µF 63V
• D1 = 1N4148
• Q1 = BC547
• Q2 = BC547
• Q3 = BC547
• Q4 = BC337
• J1 = Stereo 3mm. Jack socket
• B1 = 1.5V Battery (AA or AAA cell etc.)
• SW1 = SPST Switch (Ganged with P1)
• MIC1 = Miniature electret microphone 

 Circuit Operation :

 The heart of the circuit is a constant-volume control amplifier. All the signals picked-up by the microphone are amplified at a constant level of about 1 Volt peak to peak. In this manner very low amplitude audio signals are highly amplified and high amplitude ones are limited. This operation is accomplished by Q3, modifying the bias of Q1 (hence its AC gain) by means of R2. A noteworthy feature of this circuit is 1.5V battery operation. Typical current drawing: 7.5mA.

Notes:

1. Due to the constant-volume control, some users may consider P1 volume control unnecessary. In most cases it can be omitted, connecting C6 to C3. In this case use a SPST slider or toggle switch as SW1.
2. Please note the stereo output Jack socket (J1) connections: only the two inner connections are used, leaving open the external one. In this way the two earpieces are wired in series, allowing mono operation and optimum load impedance to Q4 (64 Ohm).
3. Using suitable miniature components, this circuit can be enclosed in a very small box, provided by a clip and hanged on one's clothes or slipped into a pocket.
4. Gary Pechon from Canada reported that the Amplified Ear is so sensitive that he can hear a whisper 7 meters across the room.
5. He hooked a small relay coil to the input and was able to locate power lines in his wall. He was also able to hear the neighbor's stereo perfectly: he could pick up the signals sent to the speaker voice coil through a plaster wall.
6. Gary suggests that this circuit could make also a good electronic stethoscope. 

Author: www.redcircuits.com
Source http://www.extremecircuits.net/2009/06/amplified-ear_28.html

09:12 0 comments

2 Transistor FM Transmitter Circuit Diagram

Warning:

Take care with transmitter circuits. It is illegal in most countries to operate radio transmitters without a license. Although only low power this circuit may be tuned to operate over the range 87-108MHz with a range of 20 or 30 metres.

Notes
I have used a pair of BC548 transistors in this circuit. Although not strictly RF transistors, they still give good results. I have used an ECM Mic insert from Maplin Electronics, order code FS43W. It is a two terminal ECM, but ordinary dynamic mic inserts can also be used, simply omit the front 10k resistor. The coil L1 was again from  Maplin, part no. UF68Y and consists of 7 turns on a quarter inch plastic former with a tuning slug. The tuning slug is adjusted to tune the transmitter. Actual range on my prototype tuned from 70MHz to around 120MHz. The aerial is a few inches of wire. Lengths of wire greater than 2 feet may damp oscillations and not allow the circuit to work. Although RF circuits are best constructed on a PCB, you can get away with veroboard, keep all leads short, and break tracks at appropriate points.

One final point, don't hold the circuit in your hand and try to speak. Body capacitance is equivalent to a 200pF capacitor shunted to earth, damping all oscillations. I have had some first hand experience of this problem. The frequency of oscillation can be found from the theory section,and an example now appears in the Circuit Analysis section. 

Source  -http://www.zen22142.zen.co.uk/Circuits/rf/2bjttx.htm

Author -Andy Collinson

08:44 0 comments

Simple Op-Amp Radio Circuit Diagram

Circuit Diagram 

Description

This is basically a crystal radio with an audio amplifier which is fairly sensitive and receives several strong stations in the Los Angeles area with a minimal 15 foot antenna. Longer antennas will provide a stronger signal but the selectivity will be worse and strong stations may be heard in the background of weaker ones. Using a long wire antenna, the selectivity can be improved by connecting it to one of the taps on the coil instead of the junction of the capacitor and coil. Some connection to ground is required but I found that standing outside on a concrete slab and just allowing the long headphone leads to lay on the concrete was sufficient to listen to the local news station (KNX 1070). The inductor was wound with 200 turns of #28 enameled copper wire on a 7/8 diameter, 4 inch length of PVC pipe, which yields about 220 uH. The inductor was wound with taps every 20 turns so the diode and antenna connections could be selected for best results which turned out to be 60 turns from the antenna end for the diode. The diode should be a germanium (1N34A type) for best results, but silicon diodes will also work if the signal is strong enough. The carrier frequency is removed from the rectified signal at the cathode of the diode by the 300 pF cap and the audio frequency is passed by the 0.1uF capacitor to the non-inverting input of the first op-amp which functions as a high impedance buffer stage. The second op-amp stage increases the voltage level about 50 times and is DC coupled to the first through the 10K resistor. If the pairs of 100K and 1 Meg resistors are not close in value (1%) you may need to either use closer matched values or add a capacitor in series with the 10K resistor to keep the DC voltage at the transistor emitter between 3 and 6 volts. Another approach would be to reduce the overall gain with a smaller feedback resistor (470K). High impedance headphones will probably work best, but walkman stereo type headphones will also work. Circuit draws about 10 mA from a 9 volt source. Germanium diodes (1N34A) types are available from Radio Shack, #276-1123.

Source - http://www.bowdenshobbycircuits.info/

13:07 0 comments

Switchable Output Crystal Oscillator Circuit Diagram

Description 

 This oscillator circuit permits crystals to be electronically switched by logic commands. The circuit is best understood by initially ignoring all crystals. Furthermore, assume that all diodes are shorts and their associated 1kO resistors open. The two 1kO resistors at the non-inverting input of IC1 (LT1016) set the output to half the supply, ie, +2.5V. The RC network from the output to pin 3 sets up phase-shifted feedback and the circuit looks like a wide-band unity gain follower at DC. When crystal X1 is inserted (remember, D1 is temporarily shorted) positive feedback occurs and oscillation commences at the crystal’s resonant frequency. 

Circuit Diagram:

 If D1 and its 1kO resistor are then considered to be part of the circuit, oscillation can only continue if logic input A is biased high. Similarly, the circuit can only operate at crystal X2’s frequency if logic input B is high. Additional crystal/diode/1kO resistor branches permit logic selection of the crystal frequency. For AT cut crystals about a millisecond is required for the circuit output to stabilise due to the high Q factors involved. Crystal frequencies can be as high as 16MHz before propagation delays in the comparator prevent reliable operation.
 Source http://www.extremecircuits.net/2010/05/switchable-output-crystal-oscillator.html

08:29 0 comments