My Maker Space - Nathan Edwards

Using a Field Programmable Analog Array for PID control of an IrDA Helicopter.

With today’s emphasis of time-to-market reduction on designs for embedded system electronics, prototyping and validation are a huge percentage of the design time that can be reduced with fast-prototyping techniques. While these techniques are abundant for digital circuitry such as utilizing soft-core IP designs on Field Programmable Gate Arrays (FGPA), analog devices typically lack reconfigurable options and yet remain an irreplaceable part of many mixed signal electronics.  However the case for using programmable analog circuits as an end solution is valid only if they meet the signal quality and timing characteristics of the desired system.  In contrast to previous work using Field Programmable Analog Arrays (FPAA) as end solutions, we will discuss a more general case of using FPAAs for design validation and fast prototyping, after which a designer could then replace the FPAA analog circuit with one that has better signal quality characteristics.

I designed a custom platform that utilizes an FPAA from Anadigm to create a PID control system for a small RC helicopter modified with an IrDA optical distance sensor.  The custom circuit board provides power and a digital configuration interface for the FPAA along with a digital-to-analog converter to provide a programmable setpoint for PID control.  The design also has a physical pin allocated to the analog voltage output of the distance measurement sensor. 

To measure the effectiveness of the system I added a dual channel analog-to-digital converter that samples the distance sensor output (PID input) and the PID output.  From the two ADC measurements we can compare the system control with the setpoint.  The overall system control and user interface is provided by the Altera Cyclone® II 2C35 FPGA (Terasic DE2 development board) running a NIOS IIe softcore processor and sending the data to an external computer for capturing the data.