Matrix keyboard encoder circuit
US4725816A · kind A · utility
Assignee
Inventor
Key dates
| Filing date | Dec 10, 1984 |
| Grant date | Feb 16, 1988 |
| Priority date | — |
| Expiry date | Dec 10, 2004 |
Classification
- Technology area (CPC H)Electricity
- CPC primaryH03M11/24
- WIPO fieldBasic communication processes
- WIPO sectorElectrical engineering
Abstract
A keyboard encoding circuit includes a first and a second set of resistors and a switching matrix divided into a plurality of switch banks, one switch bank corresponding to each resistor in the first set. Each switch bank comprises a plurality of switches with each such switch in a bank corresponding to a resistor of the second set. Each resistor in the first set has one terminal coupled in common to a supply lead of a source of DC current and a second terminal coupled to a first side of each switch in the corresponding bank of switches. Each resistor in the second resistor set has one terminal coupled to a second side of corresponding switches in one or more switch banks and a second terminal coupled to a return lead of the DC current source. The resistors in the first and second resistor sets are sized such that the actuation of any one switch produces a unique DC output voltage between the supply and return leads of the current source and such that simultaneous activation of any two or more switches produces an output voltage which is distinguishable from any output voltage produced by activation of any one switch. A digital-to-analog converter is coupled to convert the unique D…
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.