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Article: Single IC adds analog inputs to digital PLC. (integrated circuit; programmable logic controller)(Design Ideas Annual Supplement 1995)
- Article from:
- EDN
- Article date:
- February 15, 1996
- Author:
CopyrightCOPYRIGHT 1996 Reed Business Information, Inc. (US). This material is published under license from the publisher through the Gale Group, Farmington Hills, Michigan. All inquiries regarding rights should be directed to the Gale Group. (Hide copyright information)
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Many low-cost programmable logic controllers (PLCs) are digital only and have relay outputs, debounced digital inputs, and one or more counter inputs. The circuit in Fig 1 adds four 8-bit analog inputs to even the most basic PLC. The design requires a PLC with just two digital outputs and one high-speed ([is greater than] 5 kHz) counter input. The circuit is based on Microchip Technology's (Chandler, AZ) PIC 16C71 RISC [micro]C. This [micro]C has a four-channel, 8-bit ADC and an 8-bit digital I/O port. The digital I/O port has built-in pullup resistors, so direct interface to relays is possible.
[Figure 1 ILLUSTRATION OMITTED]
The PIC operates by sensing ...