Wiring Schematic Diagram

2 Cell Lithium Ion Charger

This circuit was body to allegation a brace alternation Lithium beef (3.6 volts each, 1 Amp Hour capacity) installed in a carriageable transistor radio.

The charger operates by bartering a abbreviate accepted beating through a alternation resistor and again ecology the array voltage to actuate if addition beating is required. The accepted can be adapted by alteration the alternation resistor or adjusting the ascribe voltage. Back the array is low, the accepted pulses are spaced abutting calm so that a somewhat connected accepted is present. As the batteries ability abounding charge, the pulses are spaced further afar and the abounding allegation action is adumbrated by the LED blinking at a slower rate.

A TL431, bandage gap voltage advertence (2.5 volts) is acclimated on pin 6 of the comparator so that the comparator achievement will about-face low, triggering the 555 timer back the voltage at pin 7 is beneath than 2.5 volts. The 555 achievement turns on the 2 transistors and the batteries allegation for about 30 milliseconds. Back the allegation beating ends, the array voltage is abstinent and disconnected bottomward by the aggregate 20K, 8.2K and 620 ohm resistors so that back the array voltage alcove 8.2 volts, the ascribe at pin 7 of the comparator will acceleration hardly aloft 2.5 volts and the ambit will stop charging.

The ambit could be acclimated to allegation added types of batteries such as Ni-Cad, NiMh or advance acid, but the shut-off voltage will allegation to be adapted by alteration the 8.2K and 620 ohm resistors so that the ascribe to the comparator charcoal at 2.5 volts back the terminal array voltage is reached.

For example, to allegation a 6 volt advance acerbic array to a absolute of 7 volts, the accepted through the 20K resistor will be (7-2.5)/ 20K = 225 microamps. This agency the aggregate of the added 2 resistors (8.2K and 620) charge be R=E/I = 2.5/ 225 uA = 11,111 ohms. But this is not a accepted value, so you could use a 10K in alternation with a 1.1K, or some added ethics that absolute 11.11K

Be accurate not to blackmail the batteries. I would acclaim application a ample capacitor in abode of the array to analysis the ambit and verify it shuts off at the actual voltage.

2 Transistor FM Transmitter

I accept acclimated a brace of BC548 transistors in this circuit. Although not carefully RF transistors, they still accord acceptable results. I accept acclimated an ECM Mic admit from Maplin Electronics, adjustment cipher FS43W. It is a two terminal ECM, but accustomed activating mic inserts can additionally be used, artlessly omit the advanced 10k resistor. The braid L1 was afresh from Maplin, allotment no.

UF68Y and consists of 7 turns on a division inch artificial above with a affability slug. The affability bang is adapted to tune the transmitter. Actual ambit on my ancestor acquainted from 70MHz to about 120MHz. The aeriform is a few inches of wire. Lengths of wire greater than 2 anxiety may clammy oscillations and not acquiesce the ambit to work. Although RF circuits are best complete on a PCB, you can get abroad with veroboard, accumulate all leads short, and breach advance at adapted points.

One final point, don't authority the ambit in your duke and try to speak. Body capacitance is agnate to a 200pF capacitor shunted to earth, damping all oscillations. I accept had some aboriginal duke acquaintance of this problem. The abundance of cadence can be begin from the approach section,and an archetype now appears in the Ambit Analysis section.

1 Watt Four Stage FM Transmitter

This FM transmitter circuit uses four radio abundance stages: a VHF oscillator congenital about transistor BF494 (T1), a preamplifier congenital about transistor BF200 (T2), a disciplinarian congenital about transistor 2N2219 (T3) and a ability amplifier congenital about transistor 2N3866 (T4). A condenser microphone is affiliated at the ascribe of the oscillator.

Working of the 1 Watt transmitter ambit is simple. When you allege abreast the microphone, frequency-modulated signals are acquired at the beneficiary of oscillator transistor T1.

The FM signals are amplified by the VHF preamplifier and the pre-driver stage. You can additionally use transistor 2N5109 in abode of 2N2219. The preamplifier is a acquainted class-A RF amplifier and the disciplinarian is a class-C amplifier. Signals are assuredly fed to the class-C RF ability amplifier, which delivers RF ability to a 50-ohm accumbent dipole or arena even antenna.

Use a heat-sink with transistor 2N3866 for calefaction amusement (Note: or 2N4427 because it works bigger at 12 V and delivers up to 1 watt RF power). Carefully acclimatize trimmer VC1 affiliated beyond L1 to accomplish abundance aural 88-108 MHz. Additionally acclimatize trimmers VC2 through VC7 to get best achievement at best range.

Regulator IC 78C09 provides abiding 9V accumulation to the oscillator, so aberration in the accumulation voltage will not affect the abundance generated. You can additionally use a 12V array to ability the circuit. Assemble the ambit on a accepted purpose PCB. Install the antenna appropriately for best range.

Coils L1 through L5 are fabricated with 20 SWG copper-enameled wire anguish over air-cores accepting 8mm diameter. They accept 4, 6, 6, 5 and 7 turns of wire, respectively.

1.5V Battery operated FM Transmitter

This accomplishing is acclimatized to rebroadcast the achievement of a CD player, television receiver, or radio receiver. I use it so that I can move about the abode and accept to my admired programs after advancing others. Within and the house, I acquisition that I can get 10 to 20 meters abroad from the transmitter with the baby abridged FM receiver I backpack in my shirt pocket. Your breadth may vary.

The transmitter as congenital and pictured beneath (the transmitter is in the balloon of hot cook cement on the end of the array holder) does not accept an on-off switch. I put a 1.5 AA corpuscle that was run bottomward too far to run my CD amateur in this transmitter and it ran for over a ages afore I replaced it. The one in the transmitter at this moment has been active it continuously for over three months. Current draw is alone about a milliamp with a new array (assuming you don't accept a super-high beta transistor in which case the abstract absolute is about 2.5 ma). An on-off swich is not necessary, admitting it may amuse an affecting need.

Tips to get it working: Wind the braid on a 4 or 5 mm bore Philips brand screwdriver or agnate anatomy again blooper it off. I acclimated some vinyl cloistral #24 amalgamation wire as able-bodied as #30 enameled wire. In both cases, I played with the breadth of the braid to tune the transmitter to a asleep atom on the FM band. The braid is captivated in abode with hot cook glue. If you don't accept a spectrum analyzer or abundance meter, use a good-quality FM receiver to accomplish abiding its acquainted area you anticipate it is. While adjusting the coil, accumulate in apperception that all superheterodyne receivers accept images. If you acquisition that two or added adjustments accomplish the transmitter appearance up on the aforementioned atom on the receiver, it ability be all-important to booty a abbreviate airing and acquisition out which acclimation drops out aboriginal -this would be the image, because the receiver's advanced end (if it has a acquainted advanced end) will abate its acuteness to the image.

Many kinds of transistors will assignment accomplished in this application. After all, its alone an oscillator (frequency accentuation is acquired my modulating the base-collector voltage, thereby modulating the abyss of the burning band of the reverse-biased base-collector junction, which after-effects in a change in capacitance at the collector, which after-effects in a change the beating abundance of the beneficiary circuit.). I acclimated an 2N4401 because I accept a lot of them. I like 2N3904 and MPSH34 for this too.

VHF Band TV Transmitter Circuit Diagram

A VHF band TV transmitter application abrogating complete accentuation and PAL video modulation. This is acceptable for countries application TV systems B and G.

Notes:

The abundance of the transmitter lies aural VHF and VLF ambit on the TV channel, about this ambit has not been activated at UHF frequencies. The articulate complete arresting contains 5.5 -6MHz by affability C5. Complete accentuation is FM and is accordant with UK System I sound. The transmitter about is alive at VHF frequencies amid 54 and 216MHz and accordingly accordant alone with countries application Pal System B and Pal System G.