Circuit-Zone.com - Electronic Projects
Posted on Monday, April 14, 2008 • Category: PLL Circuits
PLL Synthesizer module is an add-on based on SA1057 and PIC16F84 that converts any existing FM Transmitter into stable rock-solid PLL transmitter. Frequency is selected through 8-DIP switch. PLL Synthesizer board will also require a 100K resistor and varicap diode such as MV2105 or MV2109 to control the frequency of the transmitter's oscillator.
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.
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