Data Logging

The circuit in Figure 1 shows the versatility of the LTC2418. A combination of single-ended, differential, unipolar and bipolar input sources are simultaneously applied to the LTC2418.

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Below is a rough schematic of the layout of the accelerometer PC board looking from the component side. The microcontroller is an Atmel AT89S8252, an 8051 clone. This microcontroller is in-circuit programmable using an SPI interface. The SPI pins are also used to drive the MMC. To permit the dual use there is a jumper block (located below the 74AHC244, marked "P" and "R") that allows the pins to be connected for programming (P) or running the code (R). Speaking of the 74AHC244 chip, it MUST be the 74AHC family version. Regular old 74LS or 74HC etc. will not work, at least not for long.

The programmable data-acquisition system in Fig 1 can take 333k samples/sec using a 3-µsec sampling ADC, IC3. Multiplexer IC1 and programmable gain amplifier (PGA) IC2 provide four truly differential channels and four decade gains of 1, 10, 100, and 1000. These features allow the circuit to handle low-signal sensors without additional conditioning circuitry. The circuit does not require an S/H amplifier due to the ADC's sampling structure. If you want to handle noisy and high-speed signals, you may need to add an antialiasing filter in front of the ADC.

The circuit in Figure 1 uses a Centronics printer port to interface an eight-channel, 8-bit ADC to a PC. The circuit cuts the cost of addressing and decoder circuitry and saves one expansion slot for interfacing. The design uses three of the subport's various signals as control signals for channel selection, handshaking, and data transfer to the MAX158 ADC. These signals are programmable by means of a bit position in the control word of the respective port.

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Industrial control systems continue to employ standard analog signals for transmitting data between the process and the control equipment. Robust, 4-to-20mA current-loop signals that are easily transmitted over several thousand feet, ±5 and ±10V signals are also very common in industrial systems. This application note showcases Maxim's integrated Data Acquisition System (DAS) solutions. Maxim's DAS solutions save board space, power, and design time, while requiring minimal external components to convert standard industrial analog signals.

Analog filters can be found in almost every electronic circuit. Audio systems use them for preamplification, equalization, and tone control. In communication systems, filters are used for tuning in specific frequencies and eliminating others. Digital signal processing systems use filters to prevent the aliasing of out-of-band noise and interference.

Many PICmicro microcontroller devices have a builtin USART and it is one of the most commonly used serial interface peripherals. It is also known as the Serial Communications Interface, or SCI. The most common use of the USART is to communicate to a PC serial port using the RS-232 protocol. It has a variety of other uses however, as we will discuss in this Application Note.

When you need to test an audio circuit with broadband noise, this circuit works great. It uses just three inexpensive C-MOS ICs that generate a series of output pulses whose widths vary randomly. I included a level control pot.