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PIC Temperature Logger
Posted on Thursday, July 14, 2011   •   Category: PIC


This project uses a Microchip PIC microcontroller, a serial EEPROM and a thermistor to create a temperature recorder. The temperature is measured and stored at user programmable intervals; this can be from 1 second to 256 seconds. The time interval is set by programming it and the start time into the EEPROM. Most of the time the PIC will be asleep and the EEPROM IC is inactive. This gives a very low current consumption of approximately 50 uA or about 1 mAh per day. The EEPROM used is 32kBytes which can store up to 32,000 measurements. This could be one measurement every 30 seconds for 11 days for example. The combination of thermistor and analogue circuit gives a range of between about -40 C and +100 C although the linear range is between about -10 C and +40 C.


5 Watt Transmitter
Posted on Thursday, July 14, 2011   •   Category: FM Transmitters


This is a very simple 5 watt CW TX based upon a TTL logic chip. There is just one "tricky" component and this is Cx. This component should have an impedance of about 10 - 50 ohms at the frequency of interest. If you wish to reduce the transmitter power, increase the value of Cx. It is Cx which causes the square wave from the output transistor to approximate a sine waveform. The value of Cx is the price of simplicity in this TX.


Automatic Battery Charger
Posted on Wednesday, July 13, 2011   •   Category: Battery Chargers


Automatic battery charger automatically starts the charging procedure when battery voltage drops below a certain predefined value and stops after the voltage has risen above the maximum allowed value. Setup can't be easier, just connect two alligator clips to battery terminals and plug the device in mains. This way it can stay connected for months and the battery will never overcharge. This comes very very handy when you have a scooter or a real motorcycle that you don't drive during the winter time. Because we all know what happens to a battery when not used and especially during the winter.


Power Supplies
Posted on Wednesday, July 13, 2011   •   Category: Power Supplies


There are many types of power supply. Most are designed to convert high voltage AC mains electricity to a suitable low voltage supply for electronics circuits and other devices. A power supply can by broken down into a series of blocks, each of which performs a particular function. Each of the blocks is described in more detail below:

Transformer - steps down high voltage AC mains to low voltage AC.

Rectifier - converts AC to DC, but the DC output is varying.

Smoothing - smooths the DC from varying greatly to a small ripple.

Regulator - eliminates ripple by setting DC output to a fixed voltage.


Transistor Tester
Posted on Wednesday, July 13, 2011   •   Category: Test and Measurement


Here is a very simple circuit that can b e used to check the hfe of transistors. Both PNP and NPN transistors can be checked using this circuit. Hfe as high as 1000 can be measured by using this circuit.The circuit is based on two constant current sources build around transistors Q1 and Q2.The Q1 is a PNP transistor and the constant current flows in the emitter lead. The value of constant current can be given by the equation; (V D1 -0.6)/ (R2+R4).The POT R4 can be adjusted to get a constant current of 10uA.


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