Resolvers, or rotary-position sensors, provide a continuous output of sine and cosine signals that let control electronics determine a shaft's position. Resolvers attached to motors provide information about rotary speed and position for material cutters, printing presses, and similar equipment.
The resolver's sine and cosine signals require processing to convert them into digital values for calculation of position, revolutions per second, and so on. You can buy resolver-to-digital converters, but a fast microcontroller can do the job just as well. And the MCU can create the sine wave signal used to excite the resolver's input.
ICs in the new Delfino TMS320C2000 MCU family from Texas Instruments -- with several external components for signal conditioning -- can serve as precision synchro-to-digital converters. The MCUs also supply the hardware necessary to control motors. This application whitepaper by Ramesh Ramamoorthy, a C2000 MCU applications engineer, reviews the principles of resolver operations, describes needed signal conditioning steps, and provides a schematic diagram for external signal conditioning circuits. Those circuits need five op-amps and about 40 resistors and capacitors. TI said in a press release that programmers and engineers can get the free Delfino MCU software for the resolver applications from their local TI sales representative.
According to TI, a Delfino TMS320F28335 MCU will sample the resolver sine and cosine signals at 160 ksamples/sec, which means 16 samples per sine or cosine wave. After an initial offset compensation, the digital values pass to a control block, from which software provides angular values. The MCU also creates the excitation sine wave signal and updates it at the same sample rate. To enhance measurement accuracy, ADC sampling occurs at the peak of the sine and cosine signals received from the resolver.
Those interested in exploring the Delfino MCU capabilities and software tools can start with the free C2000 controlSUITE and Code Composer Studio integrated development environment (though there's a code limit on the free version).
An 'F28335 controlCARD (TMDSCNCD28335) costs $69 and gives you an MCU and other circuits on a 9cm x 2.5cm board that provides a standard 100-pin DIMM-type edge connector. The DM100 F28335 Experimenter's Kit (TMDSDOCK28335) costs $99 and supplies a baseboard with built-in USB-JTAG-emulation hardware (shown in the photo). TI also sells a variety of C2000 motor control kits that are compatible with Delfino microcontrollers.
Jon, in the past this would be handled by an 8-bit MCU and some other circuitry. The latest crop of 32-bit controllers with built in functionality make the 8-bit controllers obsolete.
Hi, naperlou. Right you are. And the 32-bit devices have more types of communication peripherals, too--CAN, Ethernet, USB, SPI. I2C, etc., so chip creators have moved even more hardware onto silicon. That effort makes life easier for engineers and programmers.
The death of the little 8 bitters was announced several years ago, yet they still appear to be quite live with ever expanding capability. Guess they never saw their obit, much like Mark Twains quote on the exaggeration of the rumors of his death! As far as making life easier for engineers and programmers however I will disagree. The reason is with every expansion of technology comes ever more complex solutions, and with it, ever more headaches to the designer. Think autonomous cars for example, then the redundancy that must be built into them. Engineering was never easy and will not be easy in the future. In the 60s we used two transistors to make one flip flop, thus 36 bit registers took a lot of parts. Sixty-four k "core" stacks were huge and expensive, but today I whine about having "only" 16GB in my machine.
Will 32 bit machines be replaced by 64 bit? How about 128 bit guys with far more and faster registers? What are the practical limits to bus width? ASCII is still 8 bits wide.
I have been reading a lot on load sharing processor arrays lately. Sort of like multitasking in hardware. I'm not quite ready to send my 8 bit stuff to the Smithsonian quite yet. We always live in an age of discovery and I'm very happy to be alive today.
Hi, Island_Al. Yes, plenty of life left in 8-bit MCUs for a wide variety of uses. A few days ago I sketched out a neat circuit for model-railroad enthusiasts that would use an 8-bit PIC in an 8-pin package--and an assembly-language program.
I have to disagree, 8 bits are still very much alive, especially when combined with a good compiler and plenty of memory, which is now pretty cheap. I was looking into crunching some color graphics a while ago and did two designs; one with an arm and the other with a SiLabs 8051. The 8051 was faster and cheaper in this application.
In most of the small appliances and sensors I work on, an 8 or small 16 bit machine is still my first choice. It's hard to justify a full 32 bit core when I only need 4k of code.
Hi, AndyT. The "memory" connector is actually the connector for a TI MCU "ControlCard," already in place. The odd perspective of the image places the upper edge of the ControlCard along the same line as the far edge of the small motherboard. Look again and you'll see a board plugged in. The MCU has a lot of memory. The connector lets engineers and programmers use different types of ControlCards.
Long after whatever MCU that you choose has gone out of production and is not available anywhere, thye same analog ICs will still be available from multiple makers and distributors stock. So if the anticipated product life is measured in days or months, then choose the MCU approach. But if it is a product with an expected lifetime of years, then make it out of sustainable parts. (A new expression?) Cutting edge stuff often causes bleeding.
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