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Tuesday, September 28, 2010

Wind-powered battery charger

In this wind-powered battery charger circuit the dc motor is used as a generator. The voltage output is proportional to its rpm. The LTC1042 monitors the voltage output and provides the following control function.

1. if the voltage output is below 13.8V, the control circuit is active and the NiCad battery is charging through the LM334 current source. The lead-acid battery is not being charged.
2. if the voltage output is between 13.8V and 15.1V, the 12V lead-acid battery is being charged at about 1-amp/hour rate (limited by the power FET).
3. if generator voltage exceeds 15.1V (a condition caused by excessive wind speed or when the 12V battery is fully charged), the a fixed load is connected, which limits the generator rpm to prevent damage.

This wind powered charger can be used as a remote source of power where wind energy is plentiful, such as on sailboats or at remote radio repeater sites. Unlike solar-powered panels, this system will function in bad weather and at night.
Battery Charger Schematic using wind energy

DIY Digital Thermometer

This diy digital thermometer circuit can measure temperatures up to 150°C with an accuracy of ±1°C. The temperature is read on a 1V full scale-deflection (FSD) moving-coil voltmeter or digital voltmeter.

 How the digital thermometer works

Operational amplifier IC 741 (IC3) provides a constant flow of current through the base-emitter junction of npn transistor BC108 (T1). The voltage across the base-emitter junction of the transistor is proportional to its temperature. The transistor used this way makes a low-cost sensor. You can use silicon diode instead of transistor.

The small variation in voltage across the base-emitter junction is amplified by second operational amplifier (IC4), before the temperature is displayed on the meter. Preset VR1 is used to set the zero-reading on the meter and preset VR2 is used to set the range of temperature measurement.

Operational amplifiers IC3 and IC4 operate off regulated ±5V power supply, which is derived from 3-terminal positive voltage regulator IC 7805 (IC1) and negative low-dropout regulator IC 7660 (IC2). The entire circuit works off a 9V battery.

Assemble the circuit on a general-purpose PCB and enclose in a small plastic box. Calibrate the thermometer using presets VR1 and VR2. After calibration, keep the box in the vicinity of the object whose temperature is
to be measured.

Digital Thermometer Circuit Schematic


Automatic Battery Charger

Here is a 12 volt Lead Acid battery charger that shut off the charging process once the battery attains full charge. This prevents overcharging of the battery so that, the charger can be left unattended. If the terminal voltage of the battery reduces below the set level, say 13.5 volts, the circuit automatically turns on to the charge mode.
Charging current as well as the power to the circuit is obtained from a 0-18 volt 2 Ampere step-down transformer. The low voltage AC is rectified by the bridge rectifier comprising D1 through D4 and made ripple free by the smoothing capacitor C1. For charging purpose, 18 volt DC is used while to power the circuit, 9 volt regulated DC from IC1 is used. IC2 (CA3140) is used as a simple voltage comparator to drive the relay. Its inverting input gets 4.7 volt reference voltage from the Zener ZD, while the non inverting input gets an adjustable voltage through the POT VR1.So normally, the inverting input pin 2 gets higher voltage from the Zener (as adjusted by VR1) and output of IC2 remains low. T1 then remains off keeping the relay off. The charging current passes to the battery through the NC (Normally Connected) contacts of the relay. When the terminal voltage of the battery increases to 13.5 volts, pin 3 of IC2 gets higher voltage than pin2 and the output of IC2 becomes high. This activates the relay and the contacts break. Charging current to the battery cut off and the relay remains as such since the battery voltage(13.5V or more) keeps the voltage at pin3 of IC2 is higher than that of pin 2.
Automatic Battery Charger Circuit

Setting: Before connecting the battery, set the input voltage to IC2 using a fully charged battery or variable power supply. Turn the switch S1 to the off position and switch on the power. Then connect a fully charged battery/ variable power supply to test points TP observing polarity. Measure the input voltage to pin 3 of IC2.Slowly adjust VR1 till the input voltage to pin 3 of IC2 raises to 5 volts. At this point, relay should energize and Red LED turns on. Then connect the battery for charging and switch on S1. If the battery takes charge, current to pin 3 of IC2 will be low since most of the current drain occurs into the battery. This keeps the relay off. When the battery voltage increases above 13.5 volts, no more current passes into the battery, so that the voltage at pin3 of IC2 rises and relay turns on.

3 channel RF remote control

This is a 3 channel RF remote control project.The transmitter powered by 3V battery(coin size) range about 10 m.
This remote control I use PIC12F509 from Microchip which is a 8-pin single-chip microcontroller designed for low pin count applications with 1 K words flash memory and 41Byte SRAM and some special features such Power-saving Sleep mode,Wake-up from Sleep on pin change.

The RF transmitter module for this project is TLP434A(433.92MHz) which is an Ultra Small Wireless Transmitter is ideal for remote control projects or data transfers to a remote object.This compact unit operates from only 2V up to 12V but I choose 3V for compact size
remote control in this project . A range of up to 200m is possible with an antenna fitted and 12V battery are used.This module can works directly with HT12D or similiar decoder
To reduce the standby power and extend battery life I implement by putting the PIC12F509 microcontroller into SLEEP mode for most of the time and wake-up only when a key is pressed.The standby current I measured about 100nA in sleep mode.and about 14 mA when any switch pressed.
The diode D1 and D2 is implementing ground for TLP434A when any switch pressed.Thus there are no current drawn by TLP434A when it is in standby mode.
The RLP434A which is a Compact Radio Receiver(RF) works directly with the TLP434A transmitter on an operating frequency of 433.92MHz.Ideal for many applications, including robots, where commands can be sent directly to the robot, without the need for a hard-wired connection. Suitable for data rates of up to 4.8KHz, and the typical operating current is only 4.5mA.

RS232 transceiver circuits

There are serveral rs232 transceiver circuit which commond used for communicated between microcontroller and other devices such PC or any devices that use rs232.Here is a collection of rs232 transceiver circuits that popular for today.
The circit below use 2 transistor and some components to provide RS232 transceiver.It usefull for cheap application that dose not long lenght.
 MAX232(Full duplex)
The circuit below use MAX232 which is the MAXIM's devices.This circuit is very stable and use for professional design. This device is inexpensive and it can provides 2 channel for RS232 .
The MAX232 line drivers/receivers are designed for RS-232 and V.28 communications in harsh environments. Each transmitter output and receiver input is protected against ?15kV electrostatic discharge (ESD) shocks, without latchup.It can operate from a Single +5V Power Supply.
 DS275(Half Duplex)
This RS232 transceiver circuit use DS275 which is a small half duplex transceiver chip.I Compatible with RS–232–E signals and suitible for Low–power serial transmitter/receiver for battery-
backed application.Requies no external devices.

Simple DC power delay circuit

 The circuit diagram shown here is of a simple DC power delay circuit that is based on an SCR. This circuit is a very handy one and can be employed in many applications. The working of this circuit is very simple. When the input power is applied the capacitor C2 charges through resistor R2 and when the voltage across the capacitor just exceeds the Zener diode D3’s breakdown voltage, it breaks down and the SCR H1 is triggered and the delayed power will be available at the delayed OUT terminal.