NASCAR has a show called Back in the Day, and I enjoy watching the old episodes of my boyhood heroes Petty, Allison, and Yarborough racing in real cars and fighting in the infield!

Back in the day can also apply to how some of us feel about our tractors, back when a tractor was a big beefy beast, horsepower was the biggest concern, and frilly options like cab and air were for the faint-hearted.

Tractor drivers were hard, seasoned men who wrestled machinery around the field all day and had no trouble sleeping at night due to exhaustion and exposure to the elements.

Most of those operating conditions are behind us now as modern creature comforts are the order of the day. Just as the Car of Tomorrow has evolved in NASCAR, our mechanical controls are of a bygone era, and we take for granted how nice it is to climb into the comfort of that climate controlled cab of our tractor of tomorrow.

Electrical systems back in the day included electric starting and simple lighting packages. Options were few, other than a few hitch and tire variations, and a new tractor could be ordered in a short time at the local dealership.

The last decade or so ushered in a new electronic age. Current machines offer as standard equipment many complex yet simple-to-operate electronic systems that — when properly configured — manage many sophisticated tasks.

When manufacturers incorporated the first electronic control unit on an agricultural machine, it was a basic logic unit that processed inputs from sensors, and using logic circuits, dictated outputs (commands) for machine control. Not much has changed in that arena today. ECUs have become more sophisticated, but still retain that basic input/output operating platform.

The accompanying simplified illustration shows an electronic throttle control circuit. This type circuit is common on modern equipment and uses no mechanical linkage; it is strictly fly by wire.

Using the input/output operating platform, the engine control unit receives a voltage signal (input) from the hand throttle position sensor, processes the signal using its logic circuits, and generates a command voltage to the throttle actuator located on the fuel injection pump (output). Engine speed is managed by simply altering the voltage of the input.

How is this useful? How is this an improvement over a mechanical linkage that controls engine speed? One obvious answer is accurate control. In addition to the throttle position input, engine control units monitor many other inputs, such as oil pressure coolant temperature, rpm and percent engine load and many others.

If an engine starts overheating, the engine control unit may have the ability to “derate” the engine — actually reduce the amount of fuel supplied to the engine. This feature is used to protect the engine.

A machine with manual linkage control would continue to run at full rpm, full fuel delivery, and overheat to the point that catastrophic engine failure could result.

Another benefit of this type system is that some machines offer economy mode. In this system, engine and power train controllers are connected over a network. Working together, the controllers can actually up-shift the transmission and reduce engine rpm to provide better fuel economy for the task being accomplished.

Finally, this type system has the ability to generate fault codes. These codes assist a technician in diagnosing repairs should they become necessary. Controller software is written to recognize the normal voltage operating range of a circuit. If the voltage drops below or climbs above the parameter, a code will be issued, indicating what the problem is and which circuit is involved.

Early simple controllers had sensor inputs wired directly into the controller itself. The input signals came from various types of sensors, depending on the function that was being controlled. A switch could be used as an input sensor.

For PTO control, a switch could be used to send a 12-volt signal to a controller as an input when the operator turned on the PTO function. This voltage does not power up the PTO solenoid to engage the shaft, but merely informs the controller that the operator wants the PTO turned on.

The controller reacts to the input, and processes the proper output command to the PTO solenoid, and then the PTO becomes engaged. This allows several PTO engagement safeguards to be built into the system, including a switch that indicates if the operator is seated.

Potentiometers as signaling devices have many applications on modern equipment. A potentiometer is a simple electronic signaling device that sends back a varying voltage signal which informs the controller of the current position status of the device being monitored.

I wrote about a potentiometer used as a throttle position sensor in an illustration earlier in this article. As the operator moved the throttle lever, the voltage sent to the controller varied.

Hitch control is similar. The hitch potentiometer informs the controller of the hitch height. It does this by providing a signal voltage of between 0 and 5 volts. If the signal voltage is low, the controller knows the hitch is nearly all the way down; if the signal voltage is high, the controller knows the hitch is almost all the way up.

The controller will know exactly where the hitch is positioned by looking at the signal voltage anywhere in the range of hitch travel.

If the operator moves the hitch control to raise the hitch, the controller dictates an output signal that provides pressure oil to the hitch cylinders to raise the hitch to the height the operator commanded and will stop supplying oil when this height is achieved.

This system worked well for single and standalone controller systems. A standalone system might use one controller to manage hitch functions and another controller to manage engine functions. The two controllers are not connected nor related other than being on the same machine.

Current production machines utilize multiple controllers. Many controllers need the same or common input information to accomplish their functions. To prevent having to run many wires over a machine carrying duplicate signals, a controller communication system was developed.

After evolving over a period of years, a common communications network emerged and was adopted by the ISO committee for off-road equipment, standardized with the acronym CAN (controller area network), the format used today.

With data transmission rates of 250,000 bits per second, CAN allows controllers to share information at a sizzling rate. Controllers use their own digital language to create messages that require only micro seconds to execute, providing precise, timely, and accurate feedback.

Guidance is a good example of a function that relies on CAN. A dedicated steering controller receives necessary information from many other components, such as the position receiver via CAN messages, and processes that information to keep a machine tracking on the right heading.

Electronic control units, linked by communications networks, provide continuous monitoring and precise control on equipment today. Handling tasks as complicated as guidance or as simple as returning a plow to the same depth on every pass, they increase productivity and lighten the load on the operator.

They might even get him caught up enough to make the race on Sunday.


Jimmy Presley is a technical instructor on agricultural equipment. He has spent the past 12 years developing and conducting classes for technicians across the United States. He resides in Senatobia Miss.