FAST Audio Interface Board¶
This product is not yet released
This documentation is for a product that is not yet released. Final details may change.
The FAST audio interface board offers a fully integrated pinball sound system along with several other features that normally require multiple boards. The key components include: software controlled amplifiers, automatic power handling, headphone management, LCD display control, and system watchdog. The audio interface board offers a much simpler wiring interface, especially if mounted on the back of the speaker panel. In this case only a few wires are needed to go back into the backbox. The wiring is simpler if a Raspberry Pi is used as the main controller. It easily integrates with other FAST controllers and hardware.
- 2x2 channel amplifier (main speakers and two subwoofer outputs)
- MAX9744 (data sheet PDF)
- ~15 watts usable output power (RMS) per channel (2 amps total, 4 channels: 2 for main speakers, 2 for subwoofers)
- Separate volume controls for main speakers and subwoofer
- All settings (volume, levels, headphone plug-in behavior, etc.) controlled by software (No more opening the backbox to change the volume or bass levels!)
- Designed for use with 4Ω speakers
- Separate headphone amplifier
- Built-in subwoofer low pass filter & crossover
- Headphone detection
- Interface to send commands to control machine's LCD panel settings
- PC and Raspberry Pi power and reset management
- Pinball main “power on” detector
- Main power distribution switch for external loads and amplifier power
Built-in system watchdog
Volume levels restored during power on initialization
- Raspberry Pi fan driver
- On board power supply for Raspberry Pi and amplifier drivers
- Single 12V power input
(Note most connectors have Pin 1 designated with a white arrow )
- Main Left Channel Positive Output
- Main Left Channel Negative Output
- Main Right Channel Negative Output
- Main Right Channel Positive Output
(Do not Bridge Main Speaker Outputs)
- Subwoofer 2 Positive Output
- Subwoofer 2 Negative Output
- Subwoofer 1 Negative Output
- Subwoofer 1 Positive Output
(Do not Bridge Subwoofer Outputs)
3.5mm Stereo jack * Tip = Left Channel Output * Ring = Right Channel Output * Sleeve = Ground
3.5mm Stereo jack * Tip = Left Channel Input * Ring = Right Channel Input * Sleeve = Ground
- Reset Open Drain Output
- Power Open Drain Output
- Right Angle USB Mini B
Right-angle RJ-45 jack. Connect to the FAST controller EXP or DSP bus. This is only used to detect system power. 1. Not Connected 2. Detect Negative 3. Detect Positive 4. Not Connected 5. Not Connected 6. Detect Positive 7. Detect Negative 8. Not Connected
There are two jacks for power input, one is a 2.1mm barrel jack, the other is a 0.156” two pin header. The center pin of the barrel jack is positive. Both of these connectors are electrically tied together. The positive and negative of the 0.156” connector are noted by + (positive) and - (negative) next to the connector. This input should have an upstream power supply or fuse rated for no more than 5 Amps.
There are two jacks for power output, both 0.156” two pin headers. Both of these connectors are electrically tied together. The positive and negative of the 0.156” connector are noted by + (positive) and - (negative) next to the connector. Both of these outputs are switched on by system power and can be held on by the audio controller to allow for safe system shutdown. These outputs are also fused by “PWR OUT” Fuse 1 (5x20mm). Fuse selection needs to be made based on load requirements. However, the selected fuse should be no higher than 3 Amps.
This interface connects the LCD control switches to allow software control of various features that are part of the display hardware. It can also be used to fix issues such as a display that powers up disabled. This LCD control connector is attached to the switch panel that normally comes with the display interface. It should work with any switch panel that uses common grounded switches. If a switch matrix is used for the display control, or a non-common ground approach is used, extra hardware will be necessary between the audio board and the display interface.
- Switch pin 1 control
- Switch pin 2 control
- Switch pin 3 control
- Switch pin 4 control
- Switch pin 5 control
- Switch pin 6 control
- 5V Output. This 5V output is intended to control extra hardware if needed to control the display interface. (Do not use it for any other purpose. It should be limited to 50mA maximum to manage overall system power.)
Raspberry Pi Integration¶
A Raspberry Pi can be mounted to the audio interface board as shown in the diagram above. This is optional.
The use case for this is for FAST Retro Platform games with a FAST Retro controller replacing the original MPU and this audio interface board replacing the original audio board. In this case, the Raspberry Pi attached to the audio interface can drive the "2.0" game code (with the "1.0" original game code coming from the FAST Retro Controller.) See the documentation on the FAST Retro Platform for details.
The FAST Audio Interface Board has an onboard microprocessor which connects to a controlling computer via the FAST Serial Protocol via USB or a serial control pin. When you connect to the controller via USB, a new virtual COM ports appears. (This is automatic, no drivers are needed.)
The serial port function as follows:
|Port 1||AUD||FAST Audio Processor||230400|
The exact name or number of this port will depend on your specific computer. (For example, on Windows it will be named something like COM3 or COM7. On Mac it will be like usbserial41xxx.)
The controlling PC communicates with the microprocessor by making a virtual COM port connection and then using the FAST Serial Protocol to send and receive commands and status messages. (Most of these as ASCII, meaning you can interact with your pinball machine audio interface via a terminal emulator!)
Always On Power Jumper¶
Shown in the image above is a jumper that always keeps the power on regardless of pinball main power on the detect circuit. Pre-production boards have this jumper shorted so the board can be evaluated without having a power detect method. The jumper is just a solder bridge. If you wish to test the power control function, remove the solder bridge. Note that the “power detect” function will still report correctly even with the jumper installed. See the
WD: command for more details.
All dimensions are in inches.
- 12V input maximum current: 5 amps (combined both connectors)
- 12V outputs combined: 3 amps (Fused by FUSE 1, 5x20mm)
- PC control outputs (reset, power) each output 150mA max (open drain)
- LCD control interface (6 outputs) each output 150mA max (open drain)
- All speakers outputs (main and subwoofer) are designed to drive 4 ohm loads
- Amplifier fuse (Fuse 2, 5x20mm) should be no more than 3 amps. 2.5 Amps should be used if speaker outputs are not fully loaded (only 2 or 3 speakers). If both subwoofer outputs are used, a 3 amp fuse may be necessary.
Right and left audio may be swapped on the audio input and headphone jacks due to part shortages. Final release should have everything labeled based on available connectors. Swap left and right speaker outputs to fix if swapped. As long as the headphone and line input jacks match they will be correct.
Documentation Feedback? Requests? Confused?
Hi! I'm Brian, and I'm responsible for the documentation at FAST Pinball. If you have any feedback, requests, corrections, ideas, or any other thoughts about this documentation, please let me know! You can email me at firstname.lastname@example.org. Thanks!
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