Analog to Digital

This design does not require an external power supply, because it uses the RS-232C port of the PC to satisfy its meager power requirements. Most RS-232C ports are capable of delivering a current of about 10 mA. Of this current budget, the circuit shown here consumes about 3 mA. You could use the remaining available current to power additional circuitry. The 5V for the A/D converter and the tristate switch derives from the RS-232C port's DTR and RTS signal lines.

The simple circuit in Fig 1 and an accompanying software routine let you easily substitute a multichannel 12-bit ADC for the 8-bit ADC internal to the 87C752 µC. A single assembly can then implement both the low- and high-performance version of a system. A socket lets you plug in the external ADC when you need it; otherwise, you plug in the network of 10 100V resistors. At power-up, the µC executes a routine that looks for the external converter.

This application note uses a timer IC (ICL7555), CMOS logic and discrete transistors to automatically control the conversion the MAX190 12-bit SAR analog-to-digital converter (ADC). The delay between conversions can be programed using a resistor. Logic circuits ensures proper startup when power is applied.

Long-distance optical communications and medical equipment, such as CT scanners, can benefit from a fast and accurate data-acquisition system. Optical power systems, such as laser pumps, need to constantly monitor their power levels. In such systems, the incoming laser-power range and the laser control-loop response time are such that the system needs a dynamic range of 90 dB or more and a sampling rate of 1M sample/sec.

A PC usually requires a plug-in ADC card to process analog signals. However, with the circuitry in Figure 1, a PC can communicate with an 18-bit ADC through its serial port. The port provides both positive and negative power supplies as well as control signals. IC1 is an 18-bit MAX132 ADC with a serial interface. It requires three input control signals, , DIN, and SCLK, and emits serial data, DOUT, and EOC (end-of-conversion) signals.

The circuit in Fig 1 shows a simple way to operate a 1-MHz, 12-bit ADC (IC1) in DMA mode while alternating between its two analog-input channels. The converter operates continuously, driven by the 1-MHz clock on the S/H input. Tying RD and CS low ensures that data are always present on the ADC's output bus. The outputs of the 74HC74 flip-flop, IC2, change state on the rising edge of the end-of-conversion (EOC) signal.

Fig 1 shows a Mitsubishi M50927-XXXSP/FP 4-bit microcontroller decoding a 4Χ4 keypad using only four digital I/O lines instead of eight. Saving four of a 4-bit µC's precious I/O lines couild be significant. The 4-bit µC's ADC provides the key to the savings. The µC's output lines, F1 through F4, energize the keypad's column lines one at a time via 74HC4049 buffer/ driver. If a user presses a key, the µC's ADC reads an analog voltage coresponding to the row of the pressed key.

I had a Basic Stamp project that needed to measure a nominal 12 volt battery, and I wanted a simple solution. This is the simplest I could come up with. The 555 timer will put out positive pulses. The pulse width is inversely proportional to the difference in voltage between the voltage at "ANALOG IN" and the voltage of the 4.7uF capacitor(let's say 2.5 volts). To calibrate this circuit, hook it up to a Basic Stamp measuring positive pulses, and give the circuit a known voltage.

Comparators are used for many things, but many people want to build analog-to-digital converters using a comparator. Comparators are one basic building block of all ADC architectures. A PICmicro® microcontroller with internal comparators can become an ADC with the application of some software and a minimum of external hardware. In this application note you will be shown how to build a Slope ADC. This ADC has been used with the digital pins on PICmicro microcontrollers for many years. The addition of a comparator to the circuit improves the results and reduces the power consumption.

This application note describes a high-accuracy, low-cost power meter based on the ADE7756. The design is for use in the North American 3-wire/single-phase application. This meter may also be used in a single-phase, 2-wire distribution system with a minimal amount of changes. The reference design is comprised of the ADE7756, a microcontroller, LCD display, serial interface, and power supply.