Archive for March, 2013


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Mosfet load board IRFP450

Three mosfets in parallel provide an adjustable load. Current is sensed with low side resistor. Reference is provided externally (DAC or pot).
Input voltage and current are fed into a PGA which is sent off board.
There is also an 8-bit i2c i/o expander and 18-bit i2c ADC available.

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Main components:

  • TO-247 mosfet (IRFP450)
  • TO-220 current sense resistor (35W 0.01Ω)
  • 2ch programmable gain amplifier (MCP6S22)
  • i2c 18-bit ADC (MCP3422)
  • i2c i/o expander (SX1505)

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The flight controller’s primary goal is to maneuver the aircraft in the desired manner as well as keep it from falling out of the sky. It operates by reading in data from an array of sensors as well as commands sent from the main processor. The main processor sends commands via UART communication to the XMEGA128, which acts as the control for the flight controller. The XMEGA128 then takes these commands, and runs it through different algorithms to convert the command to separate PWM signals that can be sent to the servos and motors to control the aircraft. The XMEGA128 is also reading in data from 4 seperate sensors to gain knowledge about its current orientation as well as predict its motion and help compensate for unwanted changes in position.

The first sensor that the flight controller is interfaced with is the gyroscope. The gryoscope communicates with the XMEGA128 via SPI communication protocol. The gyroscope is used to determine the angular acceleration of the aircraft, so the flight controller can determine if unwanted rotation is beginning to occur on any axis. The gyroscope that is being used is the L3G4200D by STMicroelectronics. This gryoscope offers a number of features that are beneficial to the flight controller. It offers three selectable resolution modes that give a resolution of either 250, 500, of 2000 degrees per second. This will provide us with a high accuracy for low angular accelerations as well as solid accuracy for high angular accelerations. This gyroscope also utilizes an external filter to provide better readings, which consists of R9, C9, and C10 in the schematic. To provide a more steady supply voltage and also improve results further, decoupling capacitors (C7 and C8) are added to the voltage input of the gyroscope.

In order to further monitor the position of the aircraft, two accelerometers are used on the flight controller. The accelerometers that are being utilized are the ADXL345 by Analog Devices. The reason that two accelerometers are being used is so an averaging of the two signals can be performed. Averaging the two signals will allow for a more accurate reading of the orientation of the aircraft and will help to compensate for the noise generated by the vibration of the motors and aircraft in general. The accelerometers provide many nice features including four selectable resolution modes (2G, 4G, 8G, and 16G), as well as data transfer via SPI. The accelerometers also provide programmable interrupt pins that can be used to trigger interrupts on events such as 0-G detection, and activity detection with programmable thresholds. This will allow for full customization so that the accelerometers will tailor to all of the important needs. This accelerometer also utilizes many different decoupling capacitors (C1, C2, C3 for accelerometer 1, and C4, C5, C6 for accelerometer 2) to better clean the input voltage and allow for more accurate results. The reason that three are chosen is so there is a wider frequency response to any noise generated on the line.

Another device which is being utilized is the proximity sensor. The proximity sensor that was chosen was the XLEZ4 by Max Sonar. This sensor will be used primarily in landing sequences, where a high resolution value for altitude is required. This sensor provides an accuracy of 1cm anywhere between 1cm and 765cm. This will allow the flight controller to determine its height very precisely and land without smashing into the ground. This proximity is ideal not only for its long range and high resolution, but also for its UART communication. The only issue faced with this sensor, is that it runs off of 5V, and the UART is between 0 and 5 volts. This is handled with the use of two level shifters which each consist a 2N7002 NMOS (U11 and U12) and 4 10k resistors (R10, R11, R12, and R13). These level shifters convert the 5V signals to 3.3V signals and 3.3V signals to 5V signals, all while requiring very little power to operate.

The flight controller also provides an override system for the user. It utilizes the current receiver on the aircraft, and becomes enabled when the remote control is powered on. The outputs of the receiver are connected into the flight controller and are attached to an array tri-state buffers. The servo outputs of the flight controller are also connected to an array of tri-state buffers. The tri-state buffers that are being used are the SN54HC365, which have 6 internal tri-state buffers as well as enable pins to enable all six tri-state buffers. In order to switch between the flight controller and the override, an inverter is placed on the input of one of the buffer chips, so that when the receiver triggers an override, one buffer is enabled and the other one is disabled, switching which signal is driving the servos. The inverter that is being used is a low power SN74LVC1GU04DBVR.

Lastly, the flight controller provides an array of LED’s. D1 and D2 are being used to signal that power is connected and are being current limited with R14 and R15. D3 through D10 are connected to PORTA of the XMEGA and are used for testing purposes and as status LED’s. They are being current limited by R1 through R8.

 

A common serial interface is the Inter-Integrated-Circuit (IIC) protocol, which uses only two wires (Clock and Data) allow chip to chip communications. Unlike a full duplex UART, the IIC interface uses a master and slave approach where a master (the microcontroller) initiates transfers by creating a start bit condition the slave devices listen for. When the clock line is held high and the data line transits low, this signals all the slave devices that an IIC operation is about to take place.

From this point, the master clocks out an address of the chip it wants to communicate with along with a bit indicating if it wants to write to the chip or read from it. Then commands/status or data can be sent back and forth. An acknowledge bit from the slave chip verifies to the master that the transfer has taken place and a stop bit condition from the master ends the cycle (Clock held high while data line transits from low to high).  

Most microcontrollers have at least one IIC port implemented in hardware. If not, it is relatively easy to implement a bit bang routine to communicate over any two general purpose I/O lines that can be used to create an IIC port.

To make the display IIC driven, I use the oldie but goodie; the PCF8574. This part is available from TI and from NXP and is an 8 bit parallel to IIC converter chip (See Fig. 5). Note, the three address bits (A0-A2) determine what IIC address the device will respond to. This address is encoded into the data stream so that up to 8 PCF8574’s can be connected to the same two wire IIC bus and be individually addressable and controllable.

There is also an ‘A’ version of the chip which uses a different address. The Non ‘A’ version responds to address 4x. The ‘A’ version responds to address 7x. This allows up to 16 of these devices to connect on the same IIC bus.

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By using the PCF8574 as a data pump, it is relatively easy to pump out initialization commands, display mode commands, and write to the display simply by transferring blocks of data. These blocks can be canned prompts and messages, or be constructed in RAM and sent out in one fell swoop.

To do this, I created a notation and data structure that can easily be implemented in firmware (See Fig. 6). Note, every IIC device has its own registers and functional map. The PCF8574 is no exception. Refer to the data sheets to see the specifics.

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To implement this, I used a microcontroller board I designed with a BASIC like language. It runs interpretively so I can store programs in a serial EEPROM (also IIC) and run them through commands over the serial (RS-232) port. The operator syntax is shown in Fig. 6.

I spun a small PC board with both the SIP and DIN connectors so I could use this board for virtually any type of character display. I also added the trimpot for contrast adjustments (See Fig. 7).
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For hobbyist and do-it-yourself projects, I made everything through hole to make it easier to assemble and debug. I also added redundant connectors on three sides so that these boards could snap together allowing more than one display to connect without the need for an additional cable.

 

You will note that even though only four wires are needed (clock, data, power, and ground), I made my connectors six pin. One if for interrupts because I may want to have digital I/O like push buttons sharing the same four wire bus. This approach makes a great universal front panel creation technique. Another pin is a spare — Always a good idea.

You may also notice that I added the footprints for a local power supply regulator. This way, any one of these boards can hook up to low voltage AC and supply all the others with 5 volts. Jumpers enable supplying power if needed.

This siren circuit simulates police, fire or other emergency sirens that produce an up and down wail.

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The heart of the circuit is the two transistor flasher with frequency modulation applied to the base of the first transistor. When the pushbutton is depressed, the frequency of oscillation climbs to a peak and when the button is released, the frequency descends due to the rising and falling voltage on the 22 uF capacitor. The rate of change is determined by the capacitor value and the 100k resistor from the pushbutton.  The oscillation eventually stops if the button is not depressed and the current consumption drops to a tiny level so no power switch is needed.

The 0.1 uF determines the pitch of the siren: A 0.047uF will give a higher pitch siren and a 0.001 uF will give an ultrasonic (at least for me, anyway) siren from 15 to 30 kHz which might have an interesting effect on the neighborhood dogs! The 33k resistor from the collector of the PNP to the base of the NPN widens the pulse to the speaker giving greater volume.

The flasher circuit drives a PNP transistor which powers the speaker. This transistor may be a small-signal transistor like the 2N4403 in most applications since it will not dissipate much power thanks to the rapid on-and-off switching. The 100 ohm and 100uF capacitor in series with the speaker limit the current to about 60 mA and they may be replaced with a short circuit for a louder siren as long as the transistor can take the increased current. The prototype drew about 120 mA when shorted which is fine for the 2N4403.

Transistor substitutions should be fine – try just about any small-signal transistors but avoid high frequency types so that you do not end up with unwanted RF oscillations.

This circuit simulates a chime similar to the sound many cars make when the keys are left in the ignition. The bottom two gates form a squarewave audio oscillator that drives the base of the 2N4401, turning it on and off at an audio rate. The top two gates produce a short low-going pulse about once per second that discharges the 10 uF capacitor through the diode. The voltage then jumps up and slowly decays through the 15 k collector resistor when the 2N4401 is conducting. The result is a squarewave on the collector of the 2N4401 that jumps up quickly then decays slowly. The darlington emitter-follower buffers the squarewave and drives a small speaker.  

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The tone frequency is set by the 1000 pF capacitor and the cadence of the chime is set by the 0.1 uF capacitor. The 10 uF capacitor determines how quickly the chime dies out and the 3.3 k/3.3 uF soften the attack time of the leading edge of the chime. The volume is set by the 22 ohm resistor and 100 uF bypass capacitor. These values may be experimentally varied to produce the desired sound.

This circuit is a simple mixer circuit. It can mix two signal channels and one channel is output. Using a codec circuit,Convert stereo audio to mono audio time.
-In circuit a FET number 2N3819 is main, it is better than a common transistors that a high impedane input and high gain too. so cause low noise and.. It can increase the number of channels too, By adding a VR1, R1 and C1 to the amount needed. Then connected to Buffett a new one. Most importantly is eating circuit current is very low.Can use with 9-volt batteries immediately.
When entering voice signal, one of input 1 and input 2. Audio is via C1 and C2 of each channel,served coupling signals to VR1 and VR2. To adjust the audio to the Fet Q1.Which it serves, including audio. Then expand signal the output pin S through C3 For coupling signal again, before leaving to the output.
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This is the idea of the simple audio mixer circuit. Perhaps you might need to take advantage of it.

Some time you want high gain than FET, I think an OP-AMP IC is good way for you. The LF353 has JFET within it so very well same common FET but it has many components inside it, makes high gain and better than 2N3819 but in normal using we may need it because too cost in some places.

This is a very simple 4-channel audio mixer. We used a number IC of LF353 is the main equipment, the function of each channel combined with upper signal level. They is low noise for J-fet op-amp IC.

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USB Mini Module 93C46

Image93C46 EEPROM

The USB Mini Module is a tiny PCB, the size of a standard 24 pin DIL chip. It’s a small development board that will simplify adding USB to your project.
If contains a FT8U245BM USB chip from FTDI. This chip is a complete USB interface, including the USB protocol stack.
It connects to your project through an 8-bit databus, a RD and WR line and 2 status pins. It doesn’t get simpler than this.
There’s no need to add a lot of code to handle the USB stack, all this is handles inside the FTDI chip. You just read from and write to the chip, by using the RD and WR lines, and monitoring the status flags that indicates if a character is ready, or the transmitter buffer is empty.

And there’s free OS drivers available for Windows, Linux and Macintosh computers.
These drivers work in two ways. One driver is a DLL that offers an API that you can interface to with your C or VB program. The other type adds a new comport to your PC. The speed on this new virtual comport is fixed and is the transfer rate on the USB link, typically up to 600-700 kByte/s.

This learning board has the following features:

    A 9V DC input socket with power on switch

    Regulated +5V power supply using 7805 IC

    3 output LEDs and 1 power on LED

    2 input tact switches

    2 potentiometers: one for analog input and the other for providing reference voltage for ADC

    Transistor-based TTL-RS232 level converter for serial communication.

    A DC motor with a transistor driver.

    A piezo-buzzer

Most of these features on the board are accessible through female header pins. None of the 6-I/O pins of PIC12F683 are hardwired to anything and they are accessible through header pins too. The figures  below show PIC12F683 pins, the type of female headers and jumpers used to make connection on the board, and the detail circuit diagram of the learning board. Only the ISCP pins are accessible through male header pins. The entire circuit is built on a 8 x 12 cm general prototyping board.

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 As you see the output LEDs have 470Ω current limiting resistors in series so that a PIC pin can be safely drive them. The piezo buzzer is also driven directly by a PIC pin through a series resistor. The DC motor, however, is connected as a load to the collector of S8050 transistor as the required current to drive the motor cannot be supplied by the PIC port. So, the PIC port can switch on the transistor by pulling its base HIGH and the collector current of the transistor provides the sufficient current to drive the motor.

The TTL to RS232 level converter and vice-versa is achieved with two transistors and few other components. The negative voltage required for RS232 level is stolen from the RS232 port of a PC itself. Note that there is no hardware UART inside PIC12F683, so the serial data transfer from the microcontroller to PC will be possible only through a software UART through any of GP0, GP1, GP2, GP4, and GP5 ports (GP3 is input only). The transmitter and receiver port on microcontroller side are denoted by uTx and uRx, whereas on the PC side are denoted by Tx and Rx, respectively.

The circuit diagram shows that the two input tact switches with the two potentiometer outputs and all the eight PIC12F683 pins are accessible through female headers. The tact switches are active low, i.e., under normal condition, a tact switch output is HIGH and when it is pressed, the output is LOW. There are couple of extra headers for Vcc and Gnd terminals which may be required while doing experiments.

The power supply circuit is the standard circuit of 7805 regulator IC. A power-on LED is connected across Vcc and Gnd with a 470Ω series resistor.

The in-circuit serial programming (ICSP) of PIC12F683 can be done with two pins: ICSPDAT (pin 7), and ICSPCLK (pin 6). The programming voltage, Vpp, should be provided to pin 4 of PIC12F683 while programming. All the required ISCP pins are available through a male header, so the PIC can be programmed through any ICSP PIC programmer. Make sure that the sequence of ISCP pins on the programmer side and our learning board match.

Important: During ICSP, pins 4, 6, and 7 of PIC12F683 should not be connected to anything; leave them open so that there won’t be any voltage conflict between the programmer and the external circuit.

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This portable solar charger electronic project is designed using some common electronic parts .
As you can see in circuit diagram , this portable solar charger circuit , is based on a LM358N operational amplifier and one transistor . This regulator provide a constant 2.4 volts DC and can be used for powering small devices that needs to be powered from two AA battery cells .Because the regulator has a low drop down voltage of 0.3 volt you should take care about this when you choose solar cells . Maximum load current for this solar charger electronic circuit project is around 125mA typically , enough for small portable devices like radios .

The TDA7293 has a bewildering number of options, even allowing you to add a second power stage (in another IC) in parallel with the main one. This improves power into low impedance loads, but is a rather expensive way to get a relatively small power increase. It also features muting and standby functions, although I’ve elected not to use these.

The schematic is shown in Figure 1, and is based on the PCB version. All unnecessary functions have been disabled, so it functions as a perfectly normal power amplifier. While the board is designed to take two TDA7293 ICs, it can naturally be operated with only one, and the PCB is small enough so that this is not an inconvenience. A LED is included to indicate that power is available, and because of the low current this will typically be a high brightness type.
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The IC has been shown in the same format that’s shown in the data sheet, but has been cleaned up for publication here. Since there are two amps on the board, there are two of most of the things shown, other than the power supply bypass caps and LED “Power Good” indicator. These ICs are extremely reliable (as are most power amp ICs), and to reduce the PCB size as much as possible, fuse clips and fuses have not been included. Instead, there are fusible tracks on the board that will fail if there is a catastrophic fault. While this is not an extremely reliable fuse, the purpose is to prevent power transformer failure, not to protect the amplifiers or PCB.

I normally use a gain of 23 (27dB) for all amplifiers, and the TDA7293 is specified for a minimum gain of 26dB, below which it may oscillate. Although this is only a small margin, tests so far indicate that the amp is completely stable. If you wish, you may increase the gain to 28 (29dB) to give a bit more safety margin. To do this, just change the input and feedback resistors (R3A/B and R4A/B) from 22k to 27k.

The circuit is conventional, and is very simple because all additional internal functions are unused. The LED is optional, and if you don’t think you’ll need it, it may be omitted, along with series resistor R3. All connections can be made with plugs and sockets, or hard wired. In most cases, I expect that hard wiring will be the most common, as the connectors are a pain to wire, and add unnecessary cost as well as reduce reliability.

The TDA7293 specifications might lead you to believe that it can use supply voltages of up to ±50V. With zero input signal (and therefore no output) it might, but I don’t recommend anything greater than ±35V if 4 ohm loads are expected, although ±42V will be fine if you can provide good heatsinking. In general, the lower supply voltage is more than acceptable for 99% of all applications, and higher voltages should not be used unless there is no choice. Naturally, if you can afford to lose a few ICs to experiments, then go for the 42V supplies (obtained from a 30+30V transformer).

This amp can also be bridged, using the Project 87 balanced transmitter board. You can expect about 150W into 8 ohms from a +/-35V supply. It cannot be bridged into 4 ohms, as the effective impedance on each amplifier is too low.