It is time to wrap up investigation into the workings of a tape deck faceplate, salvaged from the stock audio head unit of a 1998 Toyota Camry LE. I believe I’ve deciphered all the information necessary to reuse this faceplate independently from the rest of the tape deck. Summarized in this pinout report with links to more details.

The faceplate circuit board is largely built around a Sanyo LC75853N chip, which communicates via a Sanyo proprietary protocol called CCB (Computer Control Bus). An external microcontroller (I used an Arduino Nano in experiments to date) can dictate what is displayed on the LCD (see segment map here) and scan pressed/not-pressed state of buttons (see button map here).

Some faceplate components are independent of LC75853N:

• LCD backlight.
• Buttons backlight.
• Eject button.
• Potentiometer of volume knob. (Knob press is a scanned button.)
• Quadrature encoder of audio mode knob. (Knob press is a scanned button.)

From right-to-left, functionality I observed on these pins are:

Label	Function
ACC5V	Power supply for digital logic. +5V relative to GND
LCD-DO	CCB digital data out. LC75853N address 0x43 Single 4-byte transmission to microcontroller.
LCD-DI	CCB digital data in. Microcontroller to LC75853N address 0x42. Three 7-byte transmissions to LC75853N.
LCD-CLK	CCB clock signal. Active-low generated by microcontroller.
LCD-CE	CCB enable. Active-high generated by microcontroller.
CD-EJE	Eject button. Normally open, shorts to GND when “Eject” button is pressed.
ILL	Illumination power supply (positive). +5V to +14.4V (~60mA) relative to ILL- for variable button backlight brightness.
LCD-BL	LCD backlight power supply (positive). +6V (~60mA) relative to BL-
VOL.CON	Volume control potentiometer. Voltage between ACC5V (full clockwise) and GND (full counterclockwise)
PULS-A	Audio mode quadrature encoder knob – A ACC5V or GND, will be opposite of B when at a detent. A and B briefly identical during transition between detents.
PULS-B	Audio mode quadrature encoder knob – B ACC5V or GND, will be opposite of A when at a detent. A and B briefly identical during transition between detents.
GND	Digital logic power (negative). Relative to ACC5V
ILL-	Illumination power supply (negative) Relative to ILL
BL-	LCD backlight power supply (negative) Relative to LCD-BL
RESET	Unknown. Observed 0V relative to GND. LC75853N has no reset pin. Seems OK to leave it unconnected/floating.
	Unknown. Observed 0V relative to GND. Seems OK to leave it unconnected/floating.

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Source code for this investigation (and accompanying demo) is publicly available on GitHub.