ScarlettScroller

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Revision as of 09:53, 23 March 2022 by Bertrik (talk | contribs)

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.

Control 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

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.

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 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.