LCD reverse engineering services

LCD reverse engineering services
March 16, 2017 Eric Hawkins
In Journals

LCD Reverse Engineering services for replacement LCDs

A large share of our business originates from customers who need our LCD reverse engineering services for a replacement display module. Their current supplier has discontinued the LCD series or no longer supplies Liquid Crystal Displays.

A short time ago a customer contacted our technical engineering support department and asked if we could develop a 40×2 custom character LCD display to replace a module that their previous supplier had discontinued. They required our LCD reverse engineering services to provide a drop-in equivalent including EL backlight and exact pin-out.

The replacement display we designed is a drop-in equivalent for the pc4002ers-LSO-H character display. The Focus datasheet can be found here: FDS40x2(277×48)LBC.pdf.

This display is much larger than most character LCD displays with a length of 9.8 inches and a width of 1.5 inches. Its character height is a little over ½ inch.

This large character display is a good solution for products that need to be read at a distance. This includes industrial, test and measurement, scales and many outdoor applications.

The display is available with a backlight to make it visible in low or dark conditions. It can also be built with a sunlight readable configuration.

A brief description includes:

  • Two rows of forty characters per row
  • A viewing area of 246mm by 38mm
  • Character height of 5.2mm X 14.51mm
  • Each character is a 5×8 dot with cursor configuration
  • Built-in controller/Driver (Samsung SPLC780D or Equivalent)

This was designed as a drop-in equivalent to the pc4002 LCD series display and is a stock display at our Chandler, AZ (USA) location.

POSSIBLE DISPLAY OPTIONS INCLUDE

Although the standard display configuration is with an EL (Electro-luminescent) backlight, the character display can be manufactured with a LED (Light Emitting Diode) backlight.

An overview of LCD backlight types

EL Backlight:

Advantages of an EL backlight include:

  • Very thin LCD module, the EL backlight is less than the thickness of a credit card
  • Even light flow over the entire surface of glass, no hot or cold spots on the character Liquid Crystal Display.

Disadvantages of an EL backlight include:

  • Short half-life
  • Half-life is the amount of time before the backlight is half (or 50%) as bright as when it was first turned on. This is not the number of hours to when the backlight burns out.
  • The standard half-life of an EL backlight is 3K hours versus a LED backlight with a half-life of 50K to 90K hours (depending on driving current and desired brightness)
  • Requires AC signal
  • EL backlights are AC (Alternating Current) driven which means there needs to be an inverter on the LCD or on the customers PCB to convert the DC (Direct Current) to AC. This adds cost and requires real estate on the PCB.
  • AC signals can cause noise and interference with other electronic components
  • Higher MOQs (Minimum Order Quantities)
  • EL backlights now have a higher minimum order quantity of 500 displays per build. Focus is able to hold inventory in our Chandler warehouse if necessary.
  • Intrinsic Design considerations:
  • If the product needs to meet intrinsic design specifications, inverters cannot be incorporated since they may produce an ignition source or an arc. Intrinsic designs operate in environments, such as mines and factories, where flammable gasses may be present. The AC signal would need to be supplied from an outside power supply.
  • Limited Size
  • EL backlights are limited in their size, when a larger backlight is required, a CCFL (Cold Cathode Fluorescent Lamp) is required. The challenge is that CCFL backlights in LCDs have been phased out.

LED backlight

Advantages of a LED backlight:

  • DC driven
    • DC is the same type of power used by the LCD Display so an inverter is not required.
  • Brightness adjustment
    • It is easier to adjust the brightness of the LED backlight vs. an EL backlight. The LED brightness is reduced by limiting the driving current.
  • Backlight brightness
    • LEDs are brighter than EL backlights, they are able to provide a higher ‘NIT’ count.
    • What is an NIT?
    • The brightness of the backlight is measured in ‘nits’. As a general rule, one Nit is equal to the light produced by one candle. (It’s a bit more complicated than that, but it works out the same).

Disadvantages of LED backlights:

  • Hot and Cold Spots
    • LEDs can create hot and cold spots under the LCD glass. Most of the time the light can be ‘smoothed’ out with a diffuser, but the brighter the LED backlight is driven, the greater the chances of hot spots.
      • Note: White LED backlights have a greater tendency to produce hot spots.

It is possible to build this display with no backlight and is the best option if the display is battery powered or requires a very low power budget.

Backlight/background color

Character displays can be built in a variety of background and backlight colors. The photos below present a sampling of different options. Available colors include:

Yellow/green, grey, blue, white, red, orange, pure green, amber and others.

 

Operating temp range of character LCDs

The standard operating temperature range for this character display is -20C to 60C, but it is possible to build the display as a wide temperature version that will operate from -30C to 70C.

The cost difference is around 5%.

If the display needs to operate to a lower temperature than -30C, it would be necessary to add a heater. Contact Focus Displays for help with your custom LCD heater.

Positive Mode and Negative mode

The standard, stock display is built as a positive mode, but can be built as a negative mode.

  • Positive mode means that there are dark letters on a light colored background.
  • Negative mode means that there are light letters on a dark colored background.

Below are photos of two character displays in both positive and negative mode. Positive mode is standard, but the character LCD can be built as negative mode

The negative mode version requires the backlight to be on for the display to be readable, and is not the best solution for battery and solar powered products.

Fluid types

The standard configuration for this 40×2 character module is STN fluid, but this can be built as a TN (not recommended) or a FSTN.

TN is not recommended since it does not provide as wide of a viewing angle and has a lower contrast than the STN/FSTN option.

Below is a quick introduction to the three most common types of fluids: FSTN, STN and TN

FSTN (Film Compensated Super Twisted Nematic)

FSTN monochrome LCD displays contains a retardation film applied to the STN display to produce a black and white display. The film produces a higher contrast and wider viewing angle than STN or TN.

* Basic color options are black/white and blue/white

* FSTN is the most expensive of the three options

STN (Super Twisted Nematic)

STN monochrome LCDs require less power and are less expensive to manufacture than TFT’s. They produce a sharper contrast then TN but less sharp then FSTN. Basic color options are Gray, Blue and Yellow/Green (most common). Other colors are available through the use of filters.

* STN fluid is the most popular option today.

TN (Twisted Nematic)

TN monochrome LCDs is the lowest cost of the three options. Contrast is not as sharp as STN and FSTN. Primary color options are black letters on a gray background. Other colors are available through the use of filters.

* TN has a faster response time and performs better than STN or FSTN at colder temperatures.

LCD Reverse Engineering Summary

As mentioned at the beginning of the article. Focus Displays is able to design and build an equivalent character LCD to take the place of a discontinued display. Sometimes it may require LCD reverse engineering services.

Many times a one-time tooling or NRE (Non-Recurring Engineering) fee is required. This tooling fee is much lower for segment, character and monochrome graphic displays than it is for OLEDs (Organic light emitting diode) and TFTs (thin-film-transistor).

Necessary information needed from the customer

The primary information necessary from the customer is:

Quantity

Depending on the type of LCD technology, the MOQ could be as low as 100 to as high as 5K units. We need to know how many displays you need in a year.

Data sheets

The first step is for the customer to send Focus Displays the datasheets for the LCD they were using. If the customer does not have a current datasheet or there is a concern that it may not be accurate, Focus may be able to ‘estimate’ a cost from a photo.

If the design needs to move forward without the original data sheet, we will need a minimum of two working samples for LCD reverse engineering.

Please note: Focus will not be able to return the samples after the completion of the design.

Controller Driver information

Most LCD displays require some type of on-board controller driver processor. There are many companies that manufacture LCD IC’s. The challenge is that a controller from one company may not be 100% compatible with the controller from a second company.

If Focus is not able to locate a source for the current controller, Focus will build the prototype samples with an ‘equivalent’ IC. Chances are that the equivalent will work, but if not, the customer may be forced to modify their firmware (customer written software/code).

Focus Displays LCD Design Services

Focus Display Solutions provides off-the-shelf standard displays as well as custom LCD design services to help companies replace their current LCD. Call Focus now (480-503-4295) if you need LCD reverse engineering services. Or fill out the contact form.

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