Circuit-Zone.com - Electronic Projects
Posted on Monday, April 14, 2008 • Category: FM Transmitters
Here is the latest and greatly improved TX200 VFO/VCO FM transmitter. The most versatile transmitter to date that can be turned into high fidelity stereo PLL based 200mW FM transmitter. It is a perfect circuit for transmitting your music around the house and yard. TX200 uses only two coils; one in the oscillator and the other one in the 200mW VHF amplifier so it should be fairly easy for anyone to build. It also includes built-in pre-emphasis and C5 for enhanced sound quality. While assembling the transmitter care must be taken to make sure that C1 is directly connected to L1 and C9 to L2. These caps eliminate the distortions form the DC supply and improve the sound quality greatly. 9V voltage supply is also very important because it provides the exact amount of current to Q1 to produce loud and clear sound quality.
Posted on Friday, April 11, 2008 • Category: Battery Chargers
 Lithium Ion batteries pack a lot of power by weight compared to other types. There are 2 things that need to be handled differently than nicad on NiMH:
1. They cannot be used as a direct substitute (even if they look like other AA's) since they run at about 3.6 (or so) volts.
2. They cannot be charged in the same way as nicad or NiMH.
After a bit of research, I came up with this design.
Normally, you put in a specified current (about 0.2C) until 4.2 volts is reached. Then, you keep the voltage tightly regulated at 4.2 volts until the charge rate drops to 10 percent (about 0.02C).
This design uses a regulated supply for both parts of the charging. Only the charging current is monitored since the supply voltage is maintained at 4.2 volts. The charging current is controlled using variable pulse width of the voltage feed.
Posted on Friday, April 11, 2008 • Category: Power Supplies
 Many times we needed one relatively powerful supply in order to we supply various appliances with + 13.8V, as transceivers CB, charge lead-acid batteries, etc. The circuit it uses known completed that is capable gives in the his exit, current in continuous operation 5A and 12A peak current. It does not only need few external component. Exist a point which it will be supposed you are careful in the drawing and in board. Board has been drawn so as to exist the possibility of using also two case types completing. In the first case the IC1 in case TO-220 is placed above in pcb, in second with case TO-3, it can it�s placed above in heatsink and terminal his they are connected in the connector G3, in this case, certain we leave empty the place of IC1 above in pcb.
Posted on Friday, April 11, 2008 • Category: Frequency Wave Generators
 The Max-80 function generator IC is specified to work to 20 MHz. So far, this unit works nicely to 50KHz. Since I seldom need signals higher than that, it has taken up a happy home on my workbench and further development is iffy at best.
There are two basic approaches to controlling the frequency in this type of device. One way is to adjust the voltage to the IC manually and then read out the frequency with a counter. The problem here is you need to fiddle around with the control knob and while waiting for the one-per-second updates on the display.
The other way is to set the display with the control knob and then have the circuit diddle the control voltage to the IC until it settles on that frequency. This is done by calculating the period for the target frequency and then using the PIC to read the pulse width. It then sends short correction pulses to an integrator which controls the IC.
Posted on Friday, April 11, 2008 • Category: AVR
 This AVR ISP original by ATMEL you can found on "AVR software and technical Library - April 2003" CD-rom.It small component count I design new PCB and change some component that easy to build small PCB .The new firmware was writen by John Samperi for AT90S2313. This code can program more devices.
Posted on Friday, April 11, 2008 • Category: LED
 The idea of this project came from my youngest son. He was dreaming of a small tool able to write symbols or pictures on a screen. As a graphic LCD (even bought at Crownhill :) ) was too expensive (or too easy??), the solution adopted was to pilot a matrix of Leds. This way, with only some cheap transistors, common red Leds, and a 16F628 , the dream could become reality.
Posted on Friday, April 11, 2008 • Category: LED
 Two strips of LEDs fading in a complementary manner 9V Battery-operated portable unit. This circuit operates two LED strips in pulsing mode, i.e. one LED strip goes from off state, lights up gradually, then dims gradually, etc. while the other LED strip does the contrary. Each strip can be made up from 2 to 5 LEDs at 9V supply.
Posted on Friday, April 11, 2008 • Category: Headphone Amplifiers
 Even if simple the circuit, plirej' all condition, regarding the distortion and the response of frequency. The resistance of entry is 250K and the load that can drive is between 100R and 2K. The circuit use negative coupling. His exit functions in Class A, having as active charge the BC308 and resistance 39R. The bias current is roughly 14 mA and total 15mA. The gain of unit is 25. The power supply, can be from 6V up to 24V DC. The frequency response with load 200R, it is 37ΗΖ - 470KΗZ (-1dΒ), the output voltage is 1.5V (11mW), the distortion 0.5%.
Posted on Friday, April 11, 2008 • Category: Counters / Frequency Meters
 This simple counter is useful for frequency measurements of various wireless equipments, especially transmitters, receivers and signal generators in VHF/UHF band. Features * Display range: 0,0 to 999,9 MHz, resolution 0,1 MHz * Correct rounding, reduced blinking of last digit * Over-range indication * Fast measurement - short measuring period * High input sensitivity in VHF/UHF band * Switchable intermediate frequency offset for use with receiver.
Posted on Friday, April 11, 2008 • Category: Timer Circuits
 A small circuit that can find a lot applications of measurement time. She has the possibility us inform with sound signal from the BZ1. At the same time, exist the possibility drive a external circuit via the optocoupler IC2, after we connect the applicable circuit in contacts [ A ] and [ B ]. The circuit is based on IC1 (4060), which include in his inside, oscillator and a binary divider of 14 stage. The frequency operation of oscillator is determined by a circuit R-C that connected in pins 9,10,11 of IC1. We give supply in the circuit, with switch S1, is presented a pulse in 12 [ RESET ] via C1 and R3, null him counter, require the measurement of pulses to begin from the zero. Than the count get at in 14th digit then exit Q14 in the pin 3, acquire high logic level. This voltage drive the base the Q1-2, the transistors turn on, thus buzzer BZ1 sound, also the IC2 is ready to drive, via contacts [ A][B ], any suitable external circuit. The time delay is regulated with the potentiometer RV1, in time delay that begin from 1 minute up to 2 hours, proportionally with the combination of prices that they will have the RV1 and C2.
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