300555

1978 MODEL 30 DIGITAL PANEL METER - 2V F.S. RANGE - 5VDC POWERED - NOS W/ ORIGINAL BOX AND INSTRUCTIONS AND SCHEMATIC - The actual red 7-segment digits on the face of the meter are monolithic optoelectronic chips manufactured by Fairchild's pioneering Microwave and Optoelectronics division - Fairchild FND500 / FND507 series (or multi-digit equivalents like the FND5148). These are Common Cathode (or Common Anode depending on the driver chip pairing), single-digit GaAsP (Gallium Arsenide Phosphide) red LED displays. They are highly distinct because they use tiny, bright red LED dice bonded directly inside a standard DIP-style package - Inside the meter, an analog-to-digital converter (ADC) circuit outputs a Binary Coded Decimal (BCD) signal. This signal is sent to the 9317/7447 decoder chips, which decode the binary number into 7 distinct paths. Those paths travel through a network of current-limiting resistors directly into the pins of the FND-series LED blocks to light up the correct segments