Decoder Circuits

Figure 1 shows the block diagram for the NTE789. The input signal form the detector is amplified by a low–distortion preamplifier and simultaneously applied to both signal, generated by a local voltage–controlled oscillator (VCO), is counted down by two frequency dividers to a 38kHz signal and to two 19–kHz pilot–tone supplied by the FM detector is compared to the locally generated 19–kHz signal in a synchronous detector.

The circuit in Figure 1 represents an attempt to combine the best of both worlds: the simplicity of a rotary interface and the performance of a digital potentiometer.

No description available.

No Description available.

The TDA1591 is a monolithic bipolar integrated circuit providing the stereo decoder function and noise blanking for FM car radio applications.

The decoder's operation is more complicated than that of the encoder. A behavioral simulation (Figure 2) shows the internal signals that are involved in the decoding process. Note that the spike on the "cd" signal is not a true spike; it appears only in the behavioral simulation and disappears in postlayout simulation.

The HT-12E is a CMOS IC. This encoder serially transmits data as defined by the state of the A0 to A7 and D0 to D3 input pints. On power-up, the DOUT pin is low. The HT-12E begins a 4-word transmission cycle on receipt of a transmission enable, or TE, signal, which is active low. The cycle repeats as long as the TE signal is low. When TE goes high, the encoder completes its final 4-word transmission cycle and then stops (Figure 1).

Decoding this bit stream into ASCII hex values is an ideal job for a low-cost 8-bit microcontroller. Using a microcontroller with onboard flash memory, such as the NEC Electronics µPD78F9418A (www.necelam.com), eliminates the need for external memory. The only external components are a few discrete devices for the signal detector and the coaxial-cable loop-through (Figure 2).

The signal output by the radio control receiver is a form of PWM. This may be useful for driving servos, but is inconvenient for general electronic applications. Therefore, several of the circuits on this site convert this signal into a voltage first. This is performed by this circuit. It is not a project in its own right, just a building block used by other projects. First we must see what these signals look like. There is a document here which describes servo signals in some detail, but I’ll reproduce the timing diagram here for simplicity.

This is a simple surround sound decoder. Left & right outputs of a stereo tape or CD player can be connected to the circuit inputs and 4 outputs of the circuit can be connected to a surround power amplifier or 2 stereo power amplifier.