Forget about flea power A-V links. This one has an output of 0.5W for a range of about 200 meters using simple "whip" antennas. You will have seen adverts for devices of this type - they've become quite popular in recent years. Operating on a frequency of 2.4GHz (that's 2,400,000,000Hz for the uninitiated!), most have about 10mW or so output and while they work well over a short range, the range is limited by the low power. This design has much higher power - around 0.5W output, in fact. So as you might expect, the range is very significantly extended. With the simple coax cable "whip" antennas shown here, the range is reliably 200m or more. But if you use a simple dipole antenna, you could expect much more range - maybe 10 times or more. Perhaps a word or two about how and why this is possible is in order. It is sometimes difficult for people to understand how changing antennas can give longer range. The simplest analogy I can think of is using your own vo...
This handy circuit can be used to charge from one to 12 NiCd cells from a car battery. Up to six cells can be charged with switch S1 in the "normal" position. The LM317regulator operates as a simple current source, providing about 530mA when R1 = 2.35O (two 4.7O resistors in parallel). For more than six cells, S1 is set to the "boost" position. This applies powers to IC1, a 10W (or 20W) audio power amplifier. Positive feedback from its output (pin 4) to non-inverting input (pin 1) causes IC1 to act as a square wave oscillator. This square wave signal is coupled to the junction of Schottky diodes D1 and D2 via a 330µF capacitor, forming a conventional charge-pump voltage doubler. Over 20V (unloaded) appears at the input to REG1 - enough to charge a maximum of 12 cells! Circuit diagram:
TL431 and LM431 are relatively low-noise, stable and low-cost shunt regulators. These can be used to build all sorts of power supplies including programmable power supplies, advantages of which are enormous. You can program the output voltage with simple switches. You can also program the output voltage with digital codes coming from a microcontroller (MCU) or from the printer port of a PC. You can adjust any output voltage individually with resistors or trimmer potentiometers to the required values. This article presents a programmable power supply built around TL431 (IC1) and two bipolar transistors BD139 and TIP31 (T1 and T2). The circuit also includes an inverter 7406 (IC2), nine diodes 1N4007 (D1 through D9), a 12V regulator 7812 (IC3), a 5V regulator 7805 (IC4) and a few other components. Using this circuit you can obtain around 18V, 2A unregulated output and 3V to 15V, 1A variable regulated power supply based on digitally programmable input as shown in Table I. You can also obta...
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