PDSP1880, PDSP1881, PDSP1882, PDSP1883, PDSP1884

2006-03-30

14

Electrical and Mechanical Considerations

Voltage Transient Suppression

For best results power the display and the components that inter-

face with the display to avoid logic inputs higher than V

tionally, the LEDs may cause transients in the power supply line

while they change display states. The common practice is to place

a parallel combination of a 0.01 µF and a 22 µF capacitor between

V

ESD Protection

The input protection structure of the PDSP188X provides signifi-

cant protection against ESD damage. It is capable of withstanding

discharges greater than 4.0 kV. Take all the standard precautions

normal for CMOS components. These include properly grounding

personnel, tools, tables, and transport carriers that come in con-

tact with unshielded parts. If these conditions are not, or cannot be

met, keep the leads of the device shorted together or the parts in

anti-static packaging.

Soldering Considerations

The PDSP188X can be hand soldered with SN63 solder using a

grounded iron set to 260 °C.

Wave soldering is also possible. Use water soluble organic acid

flux or resin based RMA flux.

A wave temperature of 245 °C ± 5 °C with a dwell between 1.5 sec

to 3.0 sec can be used. Exposure to the wave should not exceed

temperatures above 260 °C for five seconds at 1.59 mm (0.063")

below the seating plane. The packages should not be immersed in

the wave.

Post Solder Cleaning Procedures

The least offensive cleaning solution is hot D.I. water (60 °C) for

less than 15 minutes. Addition of mild saponifiers is acceptable.

Do not use commercial dishwasher detergents.

For faster cleaning, solvents may be used. Exercise care in choos-

ing solvents as some may chemically attack the polycarbonate

package. Maximum exposure should not exceed two minutes at

elevated temperatures. Acceptable solvents are TF (trichorotrifluo-

rethane), and IPA.

Some major solvent manufacturers are: Allied Chemical Corpora-

tion, Specialty Chemical Division, Morristown, NJ;

Baron-Blakeslee, Chicago, IL; Dow Chemical, Midland, MI; E.I.

DuPont de Nemours & Co., Wilmington, DE.

For further information refer to Appnote 19 at www.osram-os.com

An alternative to soldering and cleaning the display modules is to

use sockets. Naturally, 28 pin DIP sockets 7.62 mm (0.300") wide

with 2.54 mm (0.100") centers work well for single displays. Multi-

ple display assemblies are best handled by longer SIP sockets or

DIP sockets when available for uniform package alignment. Socket

manufacturers are Aries Electronics, Inc., Frenchtown, NJ; Garry

Manufacturing, New Brunswick, NJ; Robinson-Nugent, New

Albany, IN; and Samtec Electronic Hardward, New Albany, IN.

Optical Considerations

The 4.70 mm (0.180") high character of the PDSP188X gives

readability up to eight feet. Proper filter selection enhances read-

ability over this distance.

Using filters emphasizes the contrast ratio between a lit LED and

the character background. This will increase the discrimination of

different characters. The only limitation is cost. Take into consider-

ation the ambient lighting environment for the best cost/benefit

ratio for filters.

Incandescent (with almost no green) or fluorescent (with almost no

red) lights do not have the flat spectral response of sunlight. Plas-

tic band-pass filters are an inexpensive and effective way to

strengthen contrast ratios. The PDSP1880 / PDSP1882 are

red / high efficiency red displays and should be matched with a

long wavelength pass filter in the 570 nm to 590 nm range. The

PDSP1883 should be matched with a yellow-green band-pass fil-

ter that peaks at 565 nm. For displays of multiple colors, neutral

density grey filters offer the best compromise.

Additional contrast enhancement is gained by shading the dis-

plays. Plastic band-pass filters with built-in louvers offer the next

step up in contrast improvement. Plastic filters can be improved

further with anti-reflective coatings to reduce glare. The trade-off is

fuzzy characters. Mounting the filters close to the display reduces

this effect. Take care not to overheat the plastic filter by allowing for

proper air flow.

Optimal filter enhancements are gained by using circular polarized,

anti-reflective, band-pass filters. The circular polarizing further

enhances contrast by reducing the light that travels through the filter

and reflects back off the display to less than 1%.

Several filter manufacturers supply quality filter materials. Some of

them are: Panelgraphic Corporation, W. Caldwell, NJ; SGL Homa-

lite, Wilmington, DE; 3M Company, Visual Products Division, St.

Paul, MN; Polaroid Corporation, Polarizer Division, Cambridge,

MA; Marks Polarized Corporation, Deer Park, NY, Hoya Optics,

Inc., Fremont, CA.

One last note on mounting filters: recessing displays and bezel

assemblies is an inexpensive way to provide a shading effect in

overhead lighting situations. Several bezel manufacturers are:

R.M.F. Products, Batavia, IL; Nobex Components, Griffith Plastic

Corp., Burlingame, CA; Photo Chemical Products of California,

Santa Monica, CA; I.E.E.-Atlas, Van Nuys, CA.