The Engine Gauges unit of the Beech Baron 58 aircraft forms a large part of the main panel right of the six-pack gauges. It shows the actual status and performance of the two engines by five dedicated indicators.
For each engine we have the following indicators:
- Manifold Pressure in InHg
- RPM in x100
- Fuel Flow in Gal / hr
- Cylinder Head Temperature (CHT) and
Exhaust Gas Temperature (EGT), both in Celsius
- Oil Temperature in Celsius and Oil Pressure in PSI
The left picture shows the arrangement within the virtual FSX cockpit and the right picture shows the implemented design as a stand-alone box to be plugged into the mid part of the main panel.
The virtual FSX design also includes an engine synchronisation indicator, located in the middle of the four upper gauges. I have ommited this indicator because there was not enough free space between the indicators. But I am pretty sure, that one can fly the plane also without this indicator.
The implemented Engine Gauges unit shows the following features:
- The ONE needle gauges are realised by step motors, because the large turn angle does not allow to use servos.
- The TWO needle gauges are realised by micro-servos.
- All mechanical parts of the gauges are 3D printed and the visible bezels are sprayed with black dull paint.
- The gauge scales were designed with Power Point and finally printed on glossy paper with a high resolution inkjet colour printer.
- The combining housing is built out of rigid FOREX foam plates and glued together. The backside plate can be disassembled by screws to allow for maintenance of the unit. The front panel was sprayed with grey paint before inserting the ten gauges.
- For each engine (left and right) there is a dedicated ATmega32 controller, which offers enough output lines for driving the step motors. Because of timing reasons it was not possible to also drive the servos by this controller. Therefore an additional ATmega8 controller is provided for driving the four servos of each engine. The communication between the ATmega32 and the ATmega8 controller is based on a 3 lines handshake procedure.
- The two ATmega32 controllers (also called sub-controllers) are controlled by a dedicated ATmega8 main-controller. The communication between the main and the sub-controllers is based on a Two-Wire-Interface (TWI) protocol. The controllers are running with a clock frequency of 10 MHz, which is sufficient to allow an uninterrupted processing of all commands from FSX.
- The communication to the PC is realised by a single serial RS-232 link from the main-controller.
- The electrical board design and layout for these controllers were made by the EAGLE PCB tool.
- Each gauge has two built-in warm white LEDs, which are dimmable depending on a day, dawn-dusk or night flight. However, the brightness of the lighting can be adjusted by the pilot by a dim turn knob, which is implemented in the lower right panel of the cockpit.
- The entire unit is powered by two separate 5V stabilised power supplies, one for the micro-controllers and a dedicated one for the step motors and the servos. This isolation avoids voltage ripples on the power line of the micro-controllers.
- The software for the main and sub-controllers was written in C using the Atmel Studio 6.
The engine gauges unit consists of two identical controller boards, one for the left and one for the right engine. Each board is basically euqipped with an ATmega32 micro-processor and two step motor driver ICs of type ULN2803. Because only 1.5 of them are necessary to drive the three step motors, the remaining half (four inverting drivers) are used to drive the illumination LEDs of the five gauges. The lower two gauges equipped with servos are driven by an additional micro-processor board based on an ATmega8 type. This separation was necessary, because the generation of the servo pulses is a time consuming procedure.
As mentioned above, the eight servos in the four lower indicators are driven by two dedicated controllers of type ATmega8. The physical design of these two controllers allow to drive up to 16 servos (8 for each controller). Because we are only driving four servos by one controller, it was decided to use the remaining eight servo lines to drive the seven servo based indicators of the mid lower cockpit panel, comprising the following gauges (implemented in L=Left Engine Controller, R=Right Engine Controller):
- Two Fuel Level Indicators (L / R)
- Two Alternator Load Indicators in Ampere (L / R)
- Electrical Power Bus Voltage (R)
- Outside Ambient Temperature in °C (L)
- Outside Ambient Pressure in hPa (L)
Although it took about 400 hours to build this unit and to develop the software, it was well worth it because this Engine Gauges unit offers all the features of the virtual FSX unit and the resulting physical design is also impressive. The complete documentation of the Engine Gauges unit, including the one for the lower mid panel is described here.