Archive for November, 2012


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When you expose the silicon die of a transistor to a light source a charge is produced. CircuitsDIY opened up a 2N3055 transistor and did some experimenting. With the help of a magnifying glass he was able to built up a charge of 0.65V and produce 42.2mA of current.

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Most photovoltaic cells are made of silicon chip above which there resides a very thin layer of noble metal through which around 1% of photon particles enter the material and activates electron flow. Here I’m showing how to make one simple solar panel using transistor.

89Sxx Development Board DS1302

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There are some 89Sxx development board, here is another one. I have designed this single side development board to be used as a tool for learning MCS-51 Microcontrollers, and for easy microcontroller project development.

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The 89Sxx development board features :

89Sxx 40-DIL based design, 89S51/52/53
In System Programming (ISP) through the 6-pin header
RS-232 and RS-485 serial port (shared pin) for communicating with serial devices like PC
HD44780 compatible alphanumeric LCD connectivity with backlight control
4 on-board tact switch
16 general purpose IO port pins on 5×2 header (Port0 and Port2)
24Cxx I2C EEPROM
DS1302 serial Real Time Clock (RTC) with battery backup
On-board supply rectifier and voltage regulator

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An in depth tutorial on the use of the 74HC595 8 bit shift register.
OK, so say you have this crazy cool idea where you need to control a ton of LEDs (I know, I know… LEDs). You looked at the multiplexer article, and that was great, but this idea is so cool, you need individual control of each LED, and turning them on one at a time just won’t do. Well again, we are here to help, and now it’s time to introduce you to the Shift Register. Not just any shift register, the super cheap, incredibly awesome 74HC595 8-bit Shift Register!

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The simplest way to drive stepper motor having lower current rating is using ULN2003. The ULN2003 contains seven darlington transistors. The ULN2003 can pass upto 500mA per channel and has an internal voltage drop of about 1V when on. It also contains internal clamp diodes to dissipate voltage spikes when driving inductive loads. The circuit for driving stepper motor using ULN2003 is shown below.

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For higher current torque motors, you can use TIP120. The advantage is that the TIP120 can pass more current along with heat sink. The disadvantages are that the more wiring is required and four TIP120 is used to control the motor.

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Now!!!!!!! I have finally solved the issue on the charging here is prototype 1 of the circuit.

LM7805 5v Regulator For USB Phone Charging

It uses 2 voltage dividers to give 2.0v to D- and 2.8v to D+, which allows smart(er) phones to take a high current. 1A should be allowed with this setup. If you want 500mA maximum, set D+ to 2.0v just as D- is.

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Note: The smoothing capacitors have been excluded from this circuit but will be included in the final design. 470uF on the regulator input, 330uF and 100nF on the output of the regulator.

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The 1Nxxxx numbering system is an American standard (now adopted globally) used to mark semiconductor devices. The “1N” means that it is a single junction semiconductor device (i.e. a diode). “4001” is a number given to the smallest diode in the 400x series (4001, 4002, and so on) – the number indicates the voltage, current and power ratings of the diode. A transistor (which has 2 junctions) would be numbered 2Nxxxx.

1-single junction semiconductor device N-Silicon device 400-its a particular series whose max allowed current is 1A. x- it denotes the voltage rating. 1-50V,2-100V,3-200V… 7-1000V.

SO, it is called 1N4001.

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LM311 is a comparator, It operates from single 5V supply or dual supplies,input current 150 nA, 50 V-50 mA output drive capability. TTL-CMOS compatible output.

The Output is open collector so it can sink current but cannot source, a totem pole output can source and sink. In this Circuit R2 is the source or pull-up.

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The Output being high or low depends on which input is more dominant or positive. If + or non-inverting input is more positive than the – inverting input then output of LM311 is high impedance or high Z as output transistor of LM311 is turned off, but output goes high due to R2 pull-up 1K, so you can apply a load of 10K and above for source. When the – input or inverting input is more positive, output goes Low as transistor turns on, now a current of upto 50mA can sink here, a LED or Relay can be driven.

On turn on C2 capacitor is discharged and pin 3 the inverting input is at a lower potential than pin 2 the non-inverting which is at 2.5V. Hence output goes high and C2 starts charging thru R5, When C2 charges a little beyond 2.5V pin 3 is more dominant and output goes low now, this slowly discharges the C2 bringing the voltage at pin 3 again below 2.5V so output goes high again. This process goes on, hence it oscillates. The charging and discharging is at the rate of R5 * C2 approx. , R3 serves as hysteresis or feedback to ensure clean turn on and off.

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The objective of the circuit is to build an electronic dice based on the functions of a 555 timer integrated circuit that operates in the astable mode.

  • LM555 – a highly stable device for generating accurate oscillation or time delays with additional terminals provided for resetting or triggering, used in linear ramp generator, pulse position and width modulation, time delay & pulse generation, sequential &precision; timing, with features such as adjustable duty cycle, temperature stability, TTL compatible output, availability in 9-pin MSOP package, timing from microseconds, and operates in both astable & monostable modes
  • 4017 – a decade counter where the count advances as the clock input becomes high that may be combined with diodes for some functions such as flash sequences
  • BC550 – an NPN general purpose transistor with low current and low voltage used for low noise stages in audio frequency equipment

The 555 IC is a highly stable device for generating oscillation or accurate time delays used in pulse width/position modulation, sequential timing, time delay generation, linear ramp generator, precision timing, and pulse generation due to its features such as normally open and normally off output, temperature stability, output and supply TTL compatible, adjustable duty cycle, and operates in both astable and monostable mode.

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The LM393 consists of two independent precision voltage comparators with an offset voltage specification as low as 2.0 mV max for two comparators which were designed specifically to operate from a single power supply over a wide range of voltages. Operation from split power
supplies is also possible and the low power supply current drain is independent of the magnitude of the power supply voltage. These comparators also have a unique characteristic in that the input common-mode voltage range includes ground, even though operated from a single power supply voltage.

Application areas include limit comparators, simple analog to digital converters; pulse, squarewave and time delay generators; wide range VCO; MOS clock timers; multivibrators
and high voltage digital logic gates. The LM393 series was designed to directly interface with TTL and CMOS. When operated from both plus and minus power supplies, the LM393 series will directly interface with MOS logic where their low power drain is a distinct advantage over standard comparators.

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This long winded intro brings me to the subject of this post: RS485.
This is a serial communications specification that uses differential signaling. The awesome thing about this is that it offers many cool things, one of which is improved noise immunity. As the wire contains the same signal twice (once normal, once inverted) When it gets to the other end, and the inverted signal is transformed into a non-inverted signal and combined with the original signal. Any electrical noise that was picked up is then cancelled out due to wave mechanics. Cool, huh?