MTCDisplay is an Arduino-based MIDI Timecode visual display that allows users to view a MIDI Timecode stream on an external LED display. The goal of this project was to create a simple display to enable lighting, audio, and video equipment operators to visually monitor a timecode stream without spending $400+ on a fully-integrated solution.
9/28/2016: Board version 1.1; see directory for changes.
8/8/2016: Board version 1.0 proven.
- MIDI IN/THRU (DIN-5 connector)
- 1x MIDI IN
- Up to 3x MIDI THRU
- 12VDC input with polarity and over-current protection
- Supports all MTC framerates (24, 25, 29.97, 30)
- Mounting holes for custom enclosures and edge clearance for extruded aluminum enclosures
- Board Dimensions: 5.00" x 3.35" (127mm x 85.09mm)
- Board Thickness: 1.6mm
- Input Power: +12VDC, 1A (max)
- Input Connections: 2.1mm DC barrel jack, MIDI (DIN-5)
- Output Connections: Up to 3x MIDI (DIN-5)
- Mounting: 4x 0.125" holes at edges of board, 0.1" clearance on sides for insertion into extruded aluminum case
MTCDisplay accepts input from a MIDI Timecode stream and displays it on a large, 7-segment display. The displays are driven and controlled by a MAX7219 driver, enabling the Arduino to focus on decoding the MIDI Timecode stream. MTCDisplay supports all four MTC framerates (24/25/29.97 drop-frame/30 frames/s), and the design can be scaled up to support almost any 7-segment, common-cathode LED display.
Timecode is a way to synchronize equipment with each other; for instance, an audio track could output a timecode stream to a lighting console so that lighting cues are triggered at exactly the right moment. MIDI Timecode (MTC) is timecode transmitted between devices using the MIDI protocol and interface, and is based off SMPTE Timecode.
You can read more about the MIDI protocol on Wikipedia or on the official MIDI Association website.
MIDI Timecode follows the SMPTE standard for timecode. Each timecode is represented as four 8-bit unsigned integers:
- Hours (hh)
- Minutes (mm)
- Seconds (ss)
- Frames (ff)
Hours, minutes and seconds are self-explanatory. Frames are sub-divisions of seconds, originally referring to a frame of film as SMPTE timecode was originally developed for film use. There are several different framerates, and as a result MIDI Timecode must also transmit the framerate to ensure all devices are kept in sync.
MIDI Timecode messages can take one of two forms:
Quarter-frame Timecode messages are used when the timecode stream is running. Each hour, minute, second or frame byte is broken down into two 4-bit values and attached to a 3-bit identifier. Before each piece is sent, it is preceded by a single status byte (0xF1).
| Piece | ID # | Data | Full Byte | Description |
|---|---|---|---|---|
| 0 | 0000 |
ffff |
0000 ffff |
Frame number lsbits |
| 1 | 0001 |
000f |
0001 000f |
Frame number msbit |
| 2 | 0010 |
ssss |
0010 ssss |
Seconds lsbits |
| 3 | 0011 |
00ss |
0011 00ss |
Seconds msbits |
| 4 | 0100 |
mmmm |
0100 mmmm |
Minutes lsbits |
| 5 | 0101 |
00mm |
0101 00mm |
Minutes msbits |
| 6 | 0110 |
hhhh |
0110 hhhh |
Hour lsbits |
| 7 | 0111 |
0rrh |
0111 0rrh |
Hour msbit and rate |
EX: Timecode = 01:02:03:04, framerate = 30 frames/s
Quarter-frame Timecode = F1 04 F1 10 F1 23 F1 30 F1 42 F1 50 F1 61 F1 76
Source: Wikipedia
If the timecode stream suddenly jumps (i.e. jumping ahead in an audio track) a full timecode is sent so that all equipment can resync. Full timecode messages are 10 bytes long, and once transmitted the MTC stream reverts back to quarter-frame messages; full timecode messages are structured as follows:
F0 7F 7F 01 01 hh mm ss ff F7
In it's current state, MTCDisplay only supports quarter-frame messages. If the timecode input jumps, the change will not be reflected on MTCDisplay until the next quarter-frame message is received.