The original 944 AFM has a spring loaded flap which the intake air pushes against. The higher the air flow the more the flap is pushed back against the spring. This flap is mechanically coupled to a potentiometer that divides the voltage supplied by the DME according to the flap position and hence the air flow (volume, not mass). The voltage supplied by the DME to the potentiometer varies by model year, the early 944’s having a higher voltage vs the later models.
This post describes how I built actuators for a Stewart platform capable of carrying a human and generating motion cues for flight simulation. Such actuators must:
As described in the previous post, the MAF and the AFM both measure airflow into an engine and output a corresponding voltage into the ECU. The AFM measures volume flow and the MAF measures MAF flow.
To emulate the AFM with the MAF, we need to determine the voltage generated by both devices at a range of air flow rates. To do this, I built the simple flow bench in the photo below:
My 1989 Porsche 944 project car has a Bosch L-Jetronic fuel injection system. A critical part of this system is the AFM (Air Flow Meter) which measures the volume + temperature of air entering the engine so that the ECU can meter the correct amount of fuel. Modern cars use a MAF (Mass Air Flow) sensor to do the same job. In this post I’m going to describe how to fit a modern VW/Audi MAF to the 944.
In this post I’m going to explain the motion control software. This software takes game data and generates motion commands to the actuators. It also provides very basic visual feedback via a GUI and control via the keyboard. The game data is in the form of rotational orientation about the three axis (roll, pitch, yaw) and three translational accelerations (heave, sway, surge). The motion commands are in the form of a length for each of the six linear actuators that move the platform relative to the base.
At the end of the previous gameboy post we ended up with a gameboy driving a modern TFT LCD, complete with pixel art upscaling in hardware. The problem though is that the various development boards are a long way from fitting in the gameboy case. I really wanted a neat solution that fits inside the original case without having to hack it about. Now that the original gameboy is a 30 year old antique, that would feel like vandalism.
This project has been in the works for about 4 years. It’s a single seat, full motion flight simulator. I’ve just got a webcam setup so I can capture it in action. Unfortunately I captured a fairly unsuccessful flight from Heathrow to London City that ends up overshooting the runway.
In the previous post I described how to use a microcontroller to adapt the LCD signals from a 30 year old gameboy to drive a modern LCD screen. While it can be made to work, it’s ultimately a dead-end. Pipelining allowed us to keep up with the gameboy but what I really want is upscaling to fill the LCD screen. This doubles the number of pixels in each line that have to be sent to the LCD in the horizontal dimension (to go from 160 to 320) and in the vertical dimension we’ll occasionally have to send two lines (to go from 144 to 240). While there might be a way forward by looking at a different microcontroller, or trying to drive the 16-bit parallel interface on the LCD, ultimately I had an itch to build some custom hardware, so that’s where we’re going.
This was a simple repair project that spiralled out of control. I came upon an original Nintendo Gameboy that had a failed LCD screen with many horizontal lines of pixels missing. I followed an online tutorial that explained how you can reheat the glue that attaches the flex cable to the LCD with a soldering iron to get it working again. Well, that didn’t work for me and I ended up burning through the flex. A quick search showed the original LCD is no longer available, and no aftermarket replacement. Game over.
I’ve decided to publish several of my personal projects on github. At the same time I’ll be posting on here to explain the build process behind them. I’ve relied heavily on generous individuals who’ve written online tutorials and posted code, so now time for me to give something back.