A computer can be used to control or automate systems. From turning lights on/off at your home to shutting down motors or heaters in industries. Speed control and PID Control too.
Control Interface to PC Ports.
PC based Instrumentation is easy to implement using USB Devices and Plugin Cards for Test and Measurement. Most instruments can communicate with PC on the GPIB interface.
Most of the sensor interface and instrument inputs are analog; even if it event based like a limit switch, analog circuit protection and signal conditioning is required before it reaches the level sensitive digital circuit blocks.
Starting with Schmitt triggers and to the VCO and A-D Converters, are grades of Mixed Circuits. I feel Comparators like LM339, Timers like the 555 and Phase Locked Loop PLL are fundamental mixed circuits as they have a analog voltage detection.
DSP and uC with built in A-D or D-A or even SOC are Public ASICs and Fall in the Embedded Systems Block. Public ASICs are not user specific, they can be branded, numbered and provided with Application notes for the use of the Design Departments of any firm. User Specific ASICs are custom built and have only an application with that manufacturer for a Specific Product type. This also protects the IP of Code and Device Design.
Here are circuits made of Resistors, Capacitors and Inductors which are passive components. Crystals, Thermistors, Varistors, Variable Passive RLC are also Passive Parts.Some circuits documented from my design note book are here with the editable schematics.
Circuits using only discrete devices
Zeners, Diodes, NPN-PNP Transistors, FET, MOSFET, SCR, Triacs are all discrete active devices. ICs and Hybrid Modules are made of many discrete and passive components.
In the Integrated Circuits or ASICs, all parts even passives are derived on the Silicon Wafer. In Hybrid Modules the construction uses SMD or Tiny Chip components interconnected in a small ceramic PCB and Hermetically Sealed if needed.
delabs designed and built many custom "engineered" Test Instruments. They were not prefect, as only one or two were fabricated. That means it will be costly to produce such instruments. It is just like tooling, you have to make some numbers to recover costs, or price it very high to compensate for the wastages and iterations. But things are better off now for building custom instruments. Yet a design firm has to make modules and keep ready, then put together a solution/system, program and ship.
Test & Measurement Instruments
When making custom equipment, you have to have an extended service agreement like 5 years. Also request a minimum order of at least 5. Make your R&D and Inventory Modular. That way it is profitable and some money available for reinvestment on instruments and Equipment for calibration and quality.
Analog Circuits are the core in any instrument design, Even in a Instrument with Digital or uC control. The Interface to the Real World parameters is Analog. High Speed Analog and High Energy Measurements are the challenging areas.
T&M and Process Control Instrumentation have many things in common; but the conditions in which a Industrial Instrument works, may be very unfriendly.
Instrumentation and Measurement Circuits
Industrial Instruments are used both in Clean-Cool Control Rooms and also in a corrosive, humid, hot and vibrating industrial environment. Even high levels of Static, Magnetic influences in conjunction with spikes and brown outs can be expected.
Basic Measurement