24-09-2012, 12:31 PM
7-Segment Numeric LED Displays
[attachment=34454]
In industrial PLC applications, one of the old, but simpler methods of displaying numeric information is to use one or more 7-Segment numeric displays connected to an output card of a PLC... Although it is possible to build such a display yourself, it is far more common to employ a pre-manufactured product such as the 4-digit panel mount unit shown at the top of this page...
To correctly interface a PLC to such a display, it helps to first understand what basic electronic components are typically employed in their makeup, and how this effects our task of interfacing to, and programming such a unit... Although both LED and LCD numeric displays are readily available, and interfaced similarly, we'll concentrate on the more common LED units in the examples to follow...
BCD to 7-Segment Decoder c/w 4-bit Latch
Once 7-Segment LED displays became readily available, a simple IC known as a "BCD to 7-Segment decoder" was quickly developed to simplify their use... Binary formatted data presented to this IC's inputs results in the IC's outputs being placed into the correct state to display the equivalent numeral (0 to 9) on a 7-Segment display...
Although BCD to 7-Segment decoder ICs are available without built in latches, this particular IC includes a built in 4-bit latch which we will make use of in later examples... For now the latch is set to simply allow input data to freely pass through to the decoder...
Multiplexed Digits
By making use of the 4-bit latches that are built into the 4511 IC, we can easily multiplex the digits if so desired... By properly controlling the state of each latch enable pin (LE) we can use the same input data lines (4 switches) to selectively write to each 7-Segment display independently... With just a minor modification to our circuit, we will be able to essentially treat each digit as a unique 4-bit memory location where BCD data of our choosing can be stored and retained...
[attachment=34454]
In industrial PLC applications, one of the old, but simpler methods of displaying numeric information is to use one or more 7-Segment numeric displays connected to an output card of a PLC... Although it is possible to build such a display yourself, it is far more common to employ a pre-manufactured product such as the 4-digit panel mount unit shown at the top of this page...
To correctly interface a PLC to such a display, it helps to first understand what basic electronic components are typically employed in their makeup, and how this effects our task of interfacing to, and programming such a unit... Although both LED and LCD numeric displays are readily available, and interfaced similarly, we'll concentrate on the more common LED units in the examples to follow...
BCD to 7-Segment Decoder c/w 4-bit Latch
Once 7-Segment LED displays became readily available, a simple IC known as a "BCD to 7-Segment decoder" was quickly developed to simplify their use... Binary formatted data presented to this IC's inputs results in the IC's outputs being placed into the correct state to display the equivalent numeral (0 to 9) on a 7-Segment display...
Although BCD to 7-Segment decoder ICs are available without built in latches, this particular IC includes a built in 4-bit latch which we will make use of in later examples... For now the latch is set to simply allow input data to freely pass through to the decoder...
Multiplexed Digits
By making use of the 4-bit latches that are built into the 4511 IC, we can easily multiplex the digits if so desired... By properly controlling the state of each latch enable pin (LE) we can use the same input data lines (4 switches) to selectively write to each 7-Segment display independently... With just a minor modification to our circuit, we will be able to essentially treat each digit as a unique 4-bit memory location where BCD data of our choosing can be stored and retained...