Size a shop floor LED sign board by its farthest reader: about 1 inch of character height per 25 ft of viewing distance, so a 75 ft line needs 3 in capitals. Confirm the data path, serial ASCII, a configured message variable or Ethernet, before ordering, and keep the press panel running until the new board matches it at controlled changes.
A sign the whole floor can read takes two decisions, not one: how big the letters have to be, and how the press value reaches the board. You already show time to completion on a small panel at the press, so the value exists and your controller can produce it. What a big board adds is distance and a second place that value has to arrive. This page gives the sizing rule, the arithmetic for a real floor line, the input options, the mounting figures, and the list to close out before the purchase order.
How big should the characters be on a shop floor sign board?
Size the board by character height and character height by distance: the working rule for LED sign boards is about 1 inch of capital letter height for every 25 ft of viewing distance, so a floor read from 75 ft needs 3 inch characters.
The 25 ft per inch figure is common practice for LED boards, and it sits between the published planning numbers for signs. The FHWA planning figure is 30 ft of viewing distance per inch of capital letter height, and 20 ft per inch is the safer choice for fast reading. A planned look passes at 30, but operators glancing up between press cycles read more easily at 25 or 20. Lighting and glare move the number too, so a board facing windows or a bright aisle deserves the next size up. This is the same distance-first logic used to size any screen by viewing distance, with inches of dot height in place of screen diagonal.
How do you measure the distance that decides the size?
Walk to the farthest station where someone actually reads the board and measure straight from eye height to the face of the sign, because that distance in feet divided by 25 sets the character height in inches.
Use the farthest reader, not the average. A 40 ft average with one station at 70 ft is a 70 ft board. Measure along the line of sight: a board mounted 12 ft up the wall gains several feet of true distance over the floor tape measure. Then walk the sightline and note what gets in the way. Rack rows, strip curtains, dust from the press and glare off the board's face at certain hours each cost readability, and the cheap fix is height and angle, decided before the board is bought. Where two bays sit at very different distances, two smaller boards beat one giant board both bays squint at.
Worked example: what does a 75 ft press line need?
A press line whose farthest operator stands 75 ft from the board needs capitals of 3 in at the standard rule and 4 in if the team reads on the move, and the arithmetic is short enough to run for your own floor.
- Character height: 75 ft ÷ 25 ft per inch = 3 in. For readers on the move: 75 ft ÷ 20 ft per inch = 3.75 in, so order the next standard size, 4 in.
- Rows: completion time, job number, press status. FHWA line spacing is 1.7 × capital height, so a 3 in row sits on a 1.7 × 3 = 5.1 in pitch, and three rows need 3 × 5.1 = 15.3 in of lit height before the frame.
- Width: the line
JOB 4127 DONE 14:35is 19 characters. A 5 × 7 dot matrix with one blank column makes each 3 in character about 6 × (3 ÷ 7) = 2.6 in wide, so the line runs 19 × 2.6 = 49 in, a board face about 4 ft wide. - Decision: a three-row board with 4 in characters and roughly a 4 ft face covers this line with margin; at 3 in characters it covers it exactly.
The same three divisions run for any floor: divide the farthest distance by 25, divide by 20 for the safer figure, and lay the rows out at 1.7 times the capital height.
LED character board or panel display: which one fits?
Pick an LED character board when the farthest reader stands beyond about 35 ft and a panel display when the whole audience is closer, because a character board's letter height is bought in inches while a screen's letter height is capped by the panel itself.
| Option | Fits when | How the value arrives | Trade to know |
|---|---|---|---|
| LED character board | Readers spread across the floor, glances from 35 ft to 100 ft or more | Serial ASCII from a controller master, a configured message variable, or Ethernet | Few rows, usually one or three colors, text only |
| Networked panel display | Stations within about 35 ft, several lines, color codes and logos wanted | Files on microSD or USB, or your own Android app over the LAN | Letter height capped by the panel; needs its own feed of fresh data |
| Existing small HMI panel kept in place | The press-side operator, during and after the cutover | Its current connection to the controller | Small audience, no new work |
The crossover comes out of the same arithmetic. A 23.8 inch panel display at 1920 × 1080 has about 11.7 in of screen height. A six-line layout at the FHWA 1.7 spacing gives capitals of 11.7 ÷ (5 × 1.7 + 1) = 11.7 ÷ 9.5 = 1.2 in, which reaches 1.2 × 30 = 36 ft at the minimum figure and 24 ft at the safe one. That is where the 35 ft line of decision comes from. Letter height on a screen rides on pixel pitch, the subject of why two panel sizes share one layout in pixels. Keeping a live value on a panel display is its own project, laid out in planning an offline sensor status display for your shop floor; the panel-display sizes live in our display range.
How does the sign get the press data from the PLC?
Before you pick a model, read the board's interface documentation and match it to what your controller can send, because the board only shows what arrives in a format it accepts; the three documented paths are serial ASCII from a master, a configured message variable, and Ethernet.
Boards built for this job are commonly fitted with one RS-232 port, one RS-485 port and one Ethernet port, and accept text from any device that can act as a serial ASCII master. An ASCII board is a listener: the controller builds a line such as JOB 4127 DONE 14:35 and pushes it out, and the board prints it. That is the master and listener arrangement described in why the HMI panel must be the serial master to the PLC. Other designs hold a set of configured messages and pick one through an update variable the controller writes, so the floor sees the message change when the variable changes. Either way the completion value already exists in your controller, because the small press panel shows it today, so the new board is a second sink, not a new calculation.
Match the port to the run. RS-232 holds to about 15 m (50 ft) at typical rates; RS-485 runs to about 1200 m (4000 ft) at low data rates, which is why multi-board floors daisy chain it; Ethernet is good for 100 m per run under the IEEE 802.3 standard, then a switch. The basis for the serial figures is in HMI to PLC serial cable maximum distance by interface. Before ordering, run the controller's driver list against the board's documented protocol, the check described in check the PLC serial protocol before replacing a legacy HMI. Bench-test one message with a known value while the board is still on the bench, then connect the controller, then mount.
Where and how high should the board hang?
Hang the board so its bottom edge clears 80 in over any walkway and rig the suspension to a 5:1 design factor, the accepted figures for overhead clearance and for anything suspended over people, then check the reading angle from each station.
The 80 in bottom edge clears the ADA figure for objects overhanging a path of travel, and it also keeps forklift drivers honest. The 5:1 factor means each anchor, wire and bracket is rated for five times the hung weight of the board. Face the board square to the main reading positions: LED boards publish a viewing angle in their specification, and a station outside that angle sees dimmed, smeared dots, so angle the board or accept taller characters for that station. Compare the board's brightness rating against the brightest condition on that wall, doors and windows included, and do the check at the brightest hour of the day. Power comes down to the feed: check the board's input voltage in its specification, and if a panel display is fed from a cabinet instead, a 24 V DC DIN-rail supply keeps the wiring on the rail.
What do you confirm before you order?
Get three answers in writing before the purchase order goes out: the board's documented input list, the exact message format it expects, and evidence your controller can produce that format, because any one of the three left open leaves you a bright, blank wall.
- Character height in inches, and the viewing distance the maker claims for each board size
- The documented input list: RS-232, RS-485, Ethernet, and whether the board accepts plain ASCII text
- The message format: fixed text, variable fields, delimiters, and how a row is selected
- What the display shows when messages stop arriving
- Input voltage, and the weight rating of the mounting hardware
Recommendation: size characters at distance ÷ 25 for readers at a fixed station and distance ÷ 20 for readers on the move, so a 75 ft line gets 3 to 4 in capitals. Choose RS-485 or Ethernet when the run from controller to board exceeds one RS-232 run, about 15 m. Bench-test one message with a known value while the board is still on the bench, and keep the existing press panel running until the big board has matched it at several controlled job changes.
So the decision for both cases reads: beyond about 35 ft to the farthest reader, a three-row LED character board with 3 to 4 in characters fed over RS-485 or Ethernet; inside 35 ft, a networked panel display sized by the same division.
Questions
How fast does the value on the board change after the controller updates it?
The wire time is small: a 19 character ASCII line at 9600 baud with 8 data bits, no parity and one stop bit is 190 bits, and 190 divided by 9600 is about 20 ms. What sets the visible lag is how often the controller builds and sends the message, so schedule the send against the press cycle and check with a stopwatch that the displayed completion time steps when the job changes.
Can the old small panel and the new board show the same value at once?
Yes, and it is the safer plan. Give each sink its own connection, a spare serial port or a network client on the controller, so the small panel and the big board are fed independently and neither depends on the other. Each sink keeps its own message configuration, so retest both after any controller program change.
What happens on the board when the controller link goes down?
That behavior is set by the board's maker, and the manual states it: some designs hold the last message, some blank the display or flash a fault. Pick a documented behavior the floor can live with. If the board holds the last message, send a periodic heartbeat line so operators can tell a live value from a frozen one, because a stale completion time read as current is worse than a blank board.
Planning information, not legal or engineering advice. Rules differ by place: check codes and permits with your local authority and your licensed trades.