| ScarlettScroller | |
|---|---|
 | |
| Participants | Bertrik |
| Skills | |
| Status | Active |
| Niche | |
| Purpose | Information viewer |
| Tool | No |
| Location | space |
| Cost | |
| Tool category | |
ScarlettScroller Property "Tool Image" (as page type) with input value "File:" contains invalid characters or is incomplete and therefore can cause unexpected results during a query or annotation process.
{{#if:No | [[Tool Owner::{{{ProjectParticipants}}} | }} {{#if:No | [[Tool Cost::{{{Cost}}} | }}
This page is about a 80x7 pixel scrolling red LED sign.
The point of the firmware is to allow it the led sign to be controlled as a framebuffer, with independent brightness control for each pixel.
Hardware
The model number is AM03127.
It has 16 elements of 5x7 red LEDs each, for a total of 80x7 LEDs. This particular board has monochrome LEDs only.
The electronics consist of two boards: a controller board and a LED board.
The LED board has the following ICs:
- SN74HC138: 3-to-8 line decoder/multiplexer
- SN74HC04: 6 inverters
- 10x SN74HC164: 8-bit parallel-out serial shift registers
- 4x APM4953: dual P-Channel Enhancement Mode Mosfet
The boards are connected through a 10 pin connector and a 5V power connector.
Control connector
Pinout:
- pin 1: SCLK
- pin 2: SCLK (shorted to pin 1)
- pin 3: G = 'green' data bit shifted into row, goes through inverter 6
- pin 4: R = 'red' data bit, goes through inverter 1
- pin 5: A = row select
- pin 6: B = row select
- pin 7: C = row select
- pin 8: D = not clear what this is, perhaps this is just another bit for the row selector, not actually used for this particular board
- pin 9: GND
- pin 10: GND
| SCLK | SCLK |
| R | G |
| B | A |
| D | C |
| GND | GND |
Unfortunately the connector does not seem to carry 5V. If that were the case, a replacement microcontroller could be powered directly from the connector, with the main power entering through the 5V power plug.
The display can be blanked by selecting row 0, e.g. signals A, B and C all 0.
Power
The control board is powered by a 12V supply and probably contains a step-down converter to turn it into 5V internally.
Theory of operation
There are 80 pixels horizontally and 10 serial-parallel chips with 8 outputs each, so one row of pixels can be kept in the shift registers.
The 3-to-8 decoder selects one particular row to light, through pins A/B/C. The MOSFETs are used as drivers.
The SCLK signal goes to the CLK input of all serial-parallel SN74HC164 chips.
The LED board is prepared to be used with R+G LED modules, however this particular board does not have the shift register populated for the dual-color.
It appears there is no 'latch' signal, although the controller board has the text 'LAT'. A latch signal could activate the row data after it's been written to the shift registers, thereby avoiding the pixels showing up already as they're being written and reducing the contrast.
Firmware
Github archive: https://github.com/bertrik/scarlettscroller
The firmware run this on an ESP8266 (wemos d1 mini), which is connected to the LED board through dupont-wire.
The firmware connects to the local wifi network (sets up a captive portal when no wifi has been configured yet). Then the framebuffer can be accessed over UDP port 8888. Just send a UDP frame consisting of 80x7 bytes, each byte representing a brightness.