Circuit knowledge

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Tuesday, November 11, 2014

78L05 7805 based 5V regulator circuit with explanation

This is a very simple article, just trying to help ….
What is the most vital piece we always need in electronics? The answer is …. a good power supply, right?

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The best regulators for using in electronic projects are the 78LXX (78L05, 78L09, 78L12, 78L15 … ). I searched google for the application notes and I found them easily (look in the bottom part of the page for the download link).
Their typical application was the IC + 2 small condensers (the input is at 0.33uF and the output is at 0.01uF), but after some tryouts and more googling I found this page which, too be honest with you, I consider it to be the best circuit over the web.
I tested the circuit and it worked like charmed.
Reading the application note we see that the input voltage must be between 7V and 20V and the output voltage is between 4.75V – 5.25V

Components:

IC1 = 78L05 / 7805
D1 = 1N4007
C1 = 100uF
C2 = 10uF

Bibliography :

http://www.pmb.co.nz/psu_general_1.htm
http://www.national.com – The official manufacturer page
The 78L05 Datasheet : http://www.national.com/ds/LM/LM78L05.pdf

Friday, October 17, 2014

ATmega88 Voting Pads System based circuit

I remember when i was a kid, i was just starting with electronics, and i was very curious about this kind of systems. They were present in every contest show on tv. It’s cool that someone developed and published a project like this. The system is controlled by an ATmega88, and the voting pads interconnect trough RS-485. After the voting is done, a Java application that runs on the PC generates bar graphs.

Monday, September 8, 2014

Telephone line Based Audio Muting and Light On Circuit

Telephone line Based Audio Muting and Light-On Circuit. Very often when enjoying music or watching TV at high audio level, we may not be able to hear a telephone ring and thus miss an important incoming phone call. To overcome this situation, the schema presented here can be used. The schema would automatically light a bulb on arrival of a telephone ring and simultaneously mute the music system/TV audio for the duration the telephone handset is off-hook. Lighting of the bulb would not only indicate an incoming call but also help in locating the telephone during darkness.
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Circuit diagram :

Telephone line Based Audio Muting and Light-On Circuit Diagram
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On arrival of a ring, or when the handset is off-hook, the inbuilt transistor of IC1 (opto-coupler) conducts and capacitor C1 gets charged and, in turn, transistor T1 gets forward biased. As a result, transistor T1 conducts, causing energisation of relays RL1, RL2, and RL3. Diode D1 connected in antiparallel to inbuilt diode of IC1, in shunt with resistor R1, provides an easy path for AC current and helps in limiting the voltage across inbuilt diode to a safe value during the ringing. (The RMS value of ring voltage lies between 70 and 90 volts RMS.) Capacitor C1 maintains necessary voltage for continuously forward biasing transistor T1 so that the relays are not energised during the negative half cycles and off-period of ring signal. Once the handset is picked up, the relays will still remain energised because of low impedance DC path available (via cradle switch and handset) for the in-built diode of IC1.

After completion of call when handset is placed back on its cradle, the low-impedance path through handset is no more available and thus relays RL1 through RL3 are deactivated. As shown in the figure, the energised relay RL1 switches on the light, while energisation of relay RL2 causes the path of TV speaker lead to be opened. (For dual-speaker TV, replace relay RL2 with a DPDT relay of 6V, 200 ohm.) Similarly, energisation of DPDT relay RL3 opens the leads going to the speakers and thus mutes both audio speakers. Use ‘NC’ contacts of relay RL3 in series with speakers of music system and ‘NC’ contacts of RL2 in series with TV speaker. Use ‘NO’ con-tact of relay RL1 in series with a bulb to get the visual indication.

Author : Dhurjati Sinha - Copyright : EFYmag

Thursday, September 4, 2014

Stereo FM Transmitter 88 108 MHz based BA1404

This is the stereo FM transmitter schematic diagram which built based BA1404. By using this HI-FI stereo FM transmitter, you will be able to transmit MP3 music from your iPod, computer, discman, walkman, TV / SAT receiver, and many other audio sources.

The transmitter can work from a single 1.5V cell battery and provide excellent crystal clear stereo sound. It can also be supplied from two 1.5V battery cells to provide the maximum range.

The kits of Stereo FM Transmitter 88-108 MHz based BA1404 available at electronics-diy.com, check it out

Thursday, August 21, 2014

Stereo PLL FM Transmitter based BH1417

Here the schema diagram of stereo PLL FM transmitter based BH1417 chip. This is certainly the most recent BH1417 FM Transmitter design diagram from RHOM that consists of lots of capabilities in a single tiny package. It includes pre-emphasis, limiter to ensure that the music can be transmitted at the same audio level, stereo encoder for stereo transmission, low pass filter that blocks any audio signals above 15KHz to avoid any RF interference, PLL schema that delivers rock solid frequency transmission (no extra frequency drift), FM oscillator and RF output buffer.

There is certainly 14 possible transmission frequencies with 200KHz increments that you can select using a 4-DIP switch. Lower band frequencies begin from 88.7 up to 89.9 MHz, and upper band frequencies begin from 107.7 up to 108.9 MHz.

BH1417 could be supplied with 4 - 6 voltage and needs only about 30mA, giving 20mW output RF power. BH1417 delivers 40dB channel separation that is fairly good, although older BA1404 FM Transmitter chip delivers slightly better 45dB channel separation.

BH1417 is only offered in SOP22 IC case so this may possibly be an inconvenience for some people. On the other hand, since the chip is smaller than common DIP-based ICs its possible to fit the whole transmitter on a compact PCB.

BH1417 chip may possibly also be applied a stand alone stereo encoder. The benefit of thats that you have full freedom of working with a transmitter and amplifier of your choice. You will still have a pre-emphasis, limiter, stereo encoder and low pass filter in a single tiny package since very few external components are required for these blocks. PIN 5 is MPX output that could be directly connected to an external FM transmitter through a 10uF capacitor.

Detailed information about this schema, visit: http://electronics-diy.com/BH1417_PLL_Stereo_FM_Transmitter.php . The kit of stereo PLL FM transmitter based BH1417 also available there.

Saturday, August 16, 2014

Cellphone Based Device Control With Voice Acknowledgement

Here is a schema that lets you operate your home appliances like lights and water pump from your office or any other remote place. So if you forgot to switch off the lights or other appliances while going out, it helps you to turn off the appliance with your cellphone. Your cellphone works as the remote control for your home appliances. You can control the desired appliance by pressing the corresponding key. The system also gives you voice acknowledgement of the appliance status.

Circuit description

Fig.1 shows the schema for cellphone based device control with voice acknowledgement. It comprises microcontroller AT89C51, DTMF decoder MT8870, voice recording/playback device APR9600 and a few discrete components.

Fig.1: Circuit for cellphone-based device control

with voice acknowledgement

Microcontroller AT89C51 is at the heart of the schema. It is a low-power, high-performance, 8-bit microcontroller with 4 kB of flash programmable and erasable read-only memory (PEROM) used as on-chip program memory, 128 bytes of RAM used as internal data memory, 32 individually programmable input/output (I/O) lines divided into four 8-bit ports, two 16-bit programmable timers/counters, a five-vector two-level interrupt architecture, on-chip oscillator and clock schemary. A 11.0592MHz crystal (XTAL1) is used to provide basic clock frequency for the microcontroller. Capacitor C3 and resistor R3 form the power-on reset schema, while push-to-on switch S20 is used for manual reset.

Port pins P1.0 through P1.7 of the microcontroller are configured to get the input from push-to-on switches S1 through S8. Pins of Port P1 are pulled high via resistor network RNW1. Port pins P2.0 through P2.4 are configured to receive the decoded DTMF signal from DTMF receiver MT8870. The functions of the corresponding switches (S1 through S8) and cellphone keys are shown in Table I.

The DTMF decoder is used for decoding the mobile signal. It gets DTMF tone from the mobile headset’s speaker pins and decodes it into 4-bit digital signal. The DTMF decoder is operated with a 3.579MHz crystal (XTAL2 ) In DTMF receiver MT8870 (IC3), capacitor C12 is used to filter the noise and resistors R6 and R7 help to amplify the input signal using the internal amplifier.

Pin 16 of IC3 connected to resistor R5 provides the early steering output. It goes high immediately when the digital algorithm detects a valid tone pair (signal condition). Any momentary loss of signal condition causes ESt to return to low state.

Pin 17 of IC3 connected to capacitor C11 is bidirectional, acting as steering input/guard time output (St/GT). A steering logic VTSt detected at St causes the device to register the detected tone pair. The guard time output resets the external steering time constant, and its state is a function of ESt and the voltage at St.

Port P3 pins P3.6 and P3.7 of IC1 are configured to select the control source for the devices. These are connected to DIP switches S17 and S18 and pulled high via resistors R2 and R1, respectively. Here, we are using two control sources, switches and mobile’s key. DIP switches S17 and S18 select the control sources as shown in Table II.

Pin 2.5 of Port P2 is configured to show the rest status. That is, if none of the control sources is selected by DIP switches S17 and S18, LED1 glows. Resistor R14 limits the current through LED1.

Voice acknowledgement is provided by the APR9600 (IC2). It is a single-chip voice recording and playback device that can record and play multiple messages at random or in sequential mode for 60 seconds. The user can select sample rates with corresponding quality recording lengths. Microphone amplifier, automatic gain control (AGC) diagram, internal anti aliasing filter, internal output amplifier and message management are some of the features of the APR9600.

Here the APR9600 is configured in random-access mode, which supports two, four and eight messages of fixed durations. The length of each message is the total recording length available divided by the total number of memory segments/tracks enabled.

Audio processor APR9600 can store up to eight voice messages. Port P0 pins and P2.7 are configured to communicate with IC2. Port P0 pins trigger selection of the message. Port pin P2.7 is the input signal to identify whether the voice message is playing or not.

Fig.2: Pin configuration

of mobile headset

Pins P3.0 through P3.5 of Port P3 control the devices with the help of relays RL1 through RL6 via relay driver IC4.

A speaker is connected to IC2 for audio output. The speaker output drives the mic input of the mobile for audio acknowledgement. An electret microphone MIC1 is connected to IC2 to record the voice in IC2. LED2 flashes to show the busy status of IC2 during recording and playback. The audio messages to be recorded in APR9600, by using trigger switches S9 through S16, are shown in Table III. SPST switch S19 is closed for recording and switch S19 is opened for playback.

Fig.3 shows the power supply schema. The 230V AC mains is stepped down by transformer X1 to deliver the secondary output of 9V, 500 mA. The transformer output is rectified by a full-wave bridge rectifier comprising diodes D1 through D4, filtered by capacitor C16 and then regulated by IC 7806 (IC5). Capacitor C15 bypasses the ripples present in the regulated 6V power supply. LED3 acts as a power-on indicator and resistor R16 limits the current through LED3.

Fig.3: Power supply schema

Recording and playback

To record the voice in IC2, follow Table III. Close SPST switch S19 to make pin 27 of IC2 low. Thereafter, press and hold switches S9 through S16 to record corresponding voice messages. LED2 flashes to indicate audio recording.

For playback of any device status, open SPST switch S19 and press the corresponding switch (S9 through S16). The recorded audio can be heard from the speaker connected to pins 14 and 15 of IC2. Fig.2 shows the pin configuration of mobile headset.

Software

The program (Device_Control.BAS) for the microcontroller is written using BASCOM microcontroller programming software. In the program, first, initialise the port (P0-P3) for corresponding controls. Thereafter, declare the variables for the program. After declaration, assign some initial value to variables. Here, microcontroller ports are initialised to make all the devices ‘off’ initially.

After that, the main function checks through ‘Do’ loop which control source has been enabled by using DIP switch pins. If you select switch S17, it searches the input from the mobile only. If you select switch S18, it searches the input from the switches (S1 through S8) only. If you enable both switch S17 and switch S18, it searches the inputs from switches and mobile. Else, the rest-status LED1 glows. Refer to Table II to select the control source.

The mobile signal is decoded into the DTMF signal by IC3. The DTMF output for each mobile key (used in this project) pressed is shown in Table IV.

After getting the input from the switches or mobile, the program goes to the device_action subroutine and executes the corresponding action (refer Table I).

The device_action subroutine changes the status of the device and calls the voice_alert subroutine. The voice_alert subroutine checks the device status and device name from the source input and controls the corresponding pins of IC2. First, it selects the voice signal for the device name. After playing that, it selects on/off status of corresponding device as mentioned in Table III.

If you press ‘*’ key followed by the device number on your mobile handset, it will not change the status of that device and inform the current device status. If you press device number followed by ‘*’ key on your mobile handset, it will change the status of that device and inform the changed device status. ‘#’ key controls the voice_control subroutine and acts like a mute key.

Sourced By: EFY