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FM Radio with TDA7000
Posted on Tuesday, May 17, 2011   •   Category: FM Radio / Receivers


This project is a FM Radio based on TDA7000 and LM386 integrated circuits. What is unusual about TDA7000 IC is how it operates. It is a proper FM superhet receiver, with the usual local oscillator, mixer, IF amplifier, limiter, and phase detector. The difference is that there's only one tuned circuit; the local oscillator. Like the Pulse Counting Receiver, the TDA7000 relies on a low IF so that ordinary Op Amp circuitry can take care of the gain and bandpass characteristics. Only 70Kc/s is used with the TDA7000. Now, you might remember that the deviation of a broadcast FM signal is +/- 75Kc/s. A fully modulated signal would therefore sound rather distorted. So, how can this IC work? It's quite simple in that there is what Philips call a Frequency Locked Loop. Basically, the local oscillator is shifted in response to detector output so that the bandwidth of the mixer output is never more than +/- 15Kc/s. It is actually compressing the frequency range of the modulated signal. The muting or squelch feature is novel to say the least. Although it performs as any other muting circuit does, the TDA7000 provides an artificial noise generator so that the receiver still sounds alive while tuned off station. If you don't need that feature, just remove the .022uF condenser at pin 3. Not all Philips data sheets show it, but connecting a 10K resistor from the supply to pin 1 will disable the squelch.


Class A Amplifier 8W
Posted on Monday, May 16, 2011   •   Category: Amplifiers


This is 8W Class A Amplifier I recently built. I am very pleased with the sonic results of this amplifier. It really does not disappoint. Even using fairly standard 3 way speakers in a large room, surprisingly there is ample power. What strikes me the most is the ability of this amplifier to differentiate between instruments and noises in the sound stage. This clarity is what I like most and I think this is achieved by deceptively simple and pure circuit topology. I used the original board layout, transistors and JFETs, and made some modifications. Heat sinking was increased to approximately triple the amount recommended. Instead of using the standard bridge rectifier, capacitor bank and battery setup, I opted for a fully regulated supply with a total of 127,0000 uF capacitance per channel and a 500 VA toroid transformer.


Automatic Battery Charger
Posted on Sunday, May 15, 2011   •   Category: Battery Chargers


Here is a simple battery charger circuit intended for 12 Volt gell-type battery. Current is limited by the 7805 regulator IC and the limiting resistor (62 ohms) to approximately 250 milliamperes, anyway most small sized gell-type battery capacities ranges from 2.5AH to 7.5AH so charging time should take several hours. When the battery is full, the regulator adjust its voltage output from 15 volts down to 5 volts automatically terminate the charging process.


Solar Battery Charger with LM317
Posted on Saturday, May 14, 2011   •   Category: Battery Chargers


This is a solar panel battery charger schematic for AA and AAA rechargeable batteries. A small solar panel would be very good as a source of voltage charger. Building a solar AA battery charger only requires a few components and a simple construction. Solar panels should be well adapted to the battery to be charged or the battery may be overcharged. If you want to charge batteries with different capacities, then you need to change the solar panels. Since this is a simple solar battery charger that does not automatically turn off when the battery is full. So we need to maintain the charging current is low enough that will not damage the battery even when they are fully charged. An LM317T voltage regulator chip that can be used with a suitable resistor to regulate current. See solar AA battery charger


Light / Dark Relay Switch
Posted on Friday, May 13, 2011   •   Category: Sensors


A simple light / dark activated relay switch circuit, suitable for many applications like the automatic switching of the lights in a shop window or a room according to the ambient light level. The circuit uses a light dependent resistor (LDR). A light/dark option has been incorporated. The term 'light/dark' is used because the circuit has a PCB-mounted switch on board. In one switch position a light-to-dark transition will activate the relay. In the other position a dark-to-light transition is required. So you can use the falling light on the detector to switch on a normally off circuit or switch off a normally on circuit. The relay is on when LDR uncovered and relay off when LDR covered. Adjust VR1 for light sensitivity. LED will turn on at the same time with relay.


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