Machine Design

Tiny micros open new frontiers

Microcontrollers keep shrinking, and the newest models are displacing old mechanical methods in a variety of applications.

Scott Fink
Principal Applications Engineer
Microchip Technology Inc.
Chandler, Ariz.

The PIC10F 8-bit Flash microcontroller family includes four devices that offer 256 to 512 instructions (3 12-bit program words) of Flash program memory and 16 to 24 bytes of data RAM memory.

Microcontrollers have been shrinking ever since their first introduction. As they get smaller, designers are using them in more and more applications including motors, motor controls, and general mechatronics.

A new microcontroller is the smallest yet. The PIC10F six-pin, 8-bit unit is packed into an ultrasmall SOT-23 package. The devices are ideal for many uses not typically served by microcontrollers, including electronic glue to fix bugs in ASICs and printed circuit boards, and to replace standard logic and timing components or traditional mechanical timers and switches.

The microcontrollers feature an internal 4-MHz oscillator, 33 instructions, two stack levels, 25-mA source/sink current I/O, along with a low-power sleep current of 100 nA. A wide operating voltage range (2 to 5.5 V) makes them suitable for many applications. Other features include an 8-bit timer, a watchdog timer, power-on reset, power-saving sleep mode, and an optional analog comparator module. With only six pins, they are compact and have a short learning curve for anyone not experienced in designing with microcontrollers.

An in-circuit serial-programming (ICSP) feature lets the devices be programmed after being mounted on a circuit board. This enables field upgrades, system calibration during manufacturing, and the addition of unique identification codes to the system.

One new application involves replacing standard logic devices in waveform generation. Microcontrollers replace traditional 555 timers, pulse-width modulators (PWMs), remote-control encoders, pulse generation, programmable frequency source, and resistor-programmable oscillators.

Another area is mechatronics, the melding of traditional mechanical functions like switches, knobs, relays, timers, and electromechanical displays with microcontrollers. Here, microcontrollers continue to replace traditional mechanical functions. One reason is their ever-smaller physical size. Internal peripherals such as accurate oscillators, brownout detection, motor drives, and communication peripherals eliminate external components. Low-power modes let microcontrollers operate in places where ultralow standby power is important, such as in a battery-operated system.

Consider throttle-position sensors used in engine-control modules (ECM). Controlling the butterfly valve with a stepper motor allows the ECM to command its position in response to varying loads, regardless of throttle position. Now that the ECM, and not a cable, controls valve position, direct fuel injection, oxygen sensors, knock sensors, and other features can be added to increase engine efficiency at little additional cost. Also, because the throttle has a communication bus, other sensors and actuators can be added that communicate with each other and the ECM on the vehicle bus, allowing advanced diagnosis and status monitoring.

Beyond the obvious advantages of reliability and durability, mechatronics can lower total system and maintenance costs by distributing the intelligence so that individual modules can do local problem detection, reporting, and correcting. In addition, the smart modules can also lower initial test and calibration issues.

Traditional mechanical shaftposition sensors used in motor positioning and volume controls use a wiper that rides on a carbon trace to provide a variable resistance. Drawbacks to this setup are that both the wiper and carbon trace wear over time, and output resistance can be affected by external noise sources. A mechatronic part replaces the wiper and carbon trace with an optical disc and microcontroller. As the disk attached to the shaft rotates, the LED alternately shines though the slots in the disk and is blocked by the space between them. The optical pickup connects to an embedded microcontroller that counts the number of times the optical sensor sees the LED. Microcontrollers add the ability to decode the quadrature signals, maintain the running count, and provide a synchronous or asynchronous serial interface. Other features such as error detection and reporting can also be added easily.

Chips keeps pumps in tip-toe shape

A new breed of controllers for motors and pumps take advantage of improvements in microcontroller chips.

The Active Intelligence controller, designed and manufactured by Mission Microsystems Inc., for ITT Industries Flojet in Foothill Ranch, Calif., consists of a PIC 10F206 microcontroller on a small PCB. The unit is embedded inside dc water pumps for RV, marine, and industrial applications and improves operation and reliability in a number of ways.

A common problem with many water pumps, such as flexible impeller and many centrifugal designs, is that they cannot run indefinitely without water (run dry) without permanently damaging the impeller and seals. The controller adds run-dry protection so the pump automatically shuts off when water is lost. It also protects against a blocked impeller and overcurrents due to locked rotors, eliminating the need for circuit breakers and fuses wired in series with the pump. It allows remote switching of high-current loads by interfacing with a low-current switch mounted a distance away from the pump, and gives remote diagnostics by blinking a lamp or LED in the remote switch.

Microchip Technology Inc.,

Mission Microsystems Inc.,

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