ScarlettScroller

This page is about a lichtkrant, brought by flok.

Hardware

It has 16 elements of 5x8 LEDs each, for a total of 80x8 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.

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 SNHC164 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.

Connector

Lichtkrant 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