1657

The General Radio 1657 Digibridge is a digital RLC meter, introduced in 1976 ¹.

Specifications

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Links

• Henry P. Hall
• US Patent 4342089, Henry P Hall, Method of and apparatus for automatic measurement of circuit parameters with microprocessor calculation techniques. Filed Dec 12, 1979; Granted July 27, 1982
• How to measure R, C, L using vintage LCR meter @ YouTube
• Gipe, M.A., Hall, H.P. and Sullivan, R., "Microprocessor Simplifies Impedance Measurements", Session 1, Paper #4, Wescon 1976
• Hall, H.P., "Analog tests: the microprocessor scores" IEEE Spectrum, April 1977
• 1657 description, disassembly and Verilog simulation @ tauntek.com

Internals

The 1657 applies a sine wave to the measured device and a precision resistor in series. The average voltage across each is measured using four different phases relative to the input sine wave, for a total of eight measurements. From these, the resistive and reactive components of the tested device are calculated and displayed.

The 1657 uses a 6503 CPU, which is a 28-pin version of the 6502 with the same instruction set, but fewer address lines. The 1657's firmware is contained in a 2Kx8 ROM, in later versions a 2716 EPROM. A 128-byte SRAM holds scratchpad and the stack.

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