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 The Latest Epson 5th generation Micro Piezo Printhead can reach resolution of 1440 dpi. It's extremely fine ink droplets are able to fully reflect the rich detail of the picture, and to fulfill the requirement of one meter viewing range. Suitable for both water based dye and eco-solvent pigment inks, And it can offer one to two years service life.

 

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Symbol of LED

LEDs emit light when an electric current passes through them.

Testing an LED
Never connect an LED directly to a battery or power supply!
It will be destroyed almost instantly because too much current will pass through and burn it out.

LEDs must have a resistor in series to limit the current to a safe value, for quick testing purposes a 1kΩ resistor is suitable for most LEDs if your supply voltage is 12V or less. 

Remember to connect the LED the correct way round!

Colors of LEDs
LEDs are available in red, orange, amber, yellow, green, blue and white. Blue and white LEDs are much more expensive than the other colors.

The color of an LED is determined by the semiconductor material, not by the coloring of the 'package' (the plastic body). LEDs of all colors are available in uncolored packages which may be diffused (milky) or clear (often described as 'water clear'). The colored packages are also available as diffused (the standard type) or transparent.

Tri-color LEDs
The most popular type of tri-color LED has a red and a green LED combined in one package with three leads. They are called tri-color because mixed red and green light appears to be yellow and this is produced when both the red and green LEDs are on.

The diagram shows the construction of a tri-color LED. Note the different lengths of the three leads. The centre lead (k) is the common cathode for both LEDs, the outer leads (a1 and a2) are the anodes to the LEDs allowing each one to be lit separately, or both together to give the third color.

Avoid connecting LEDs in parallel!
 

Connecting several LEDs in parallel with just one resistor shared between them is generally not a good idea.

If the LEDs require slightly different voltages only the lowest voltage LED will light and it may be destroyed by the larger current flowing through it. Although identical LEDs can be successfully connected in parallel with one resistor this rarely offers any useful benefit because resistors are very cheap and the current used is the same as connecting the LEDs individually.

If LEDs are in parallel each one should have its own resistor.

Type Color IF
max.
VF
typ.
VF
max.
VR
max.
Luminous
intensity
Viewing
angle
Wavelength
Standard Red 30mA 1.7V 2.1V 5V 5mcd @ 10mA 60 660nm
Standard Bright red 30mA 2.0V 2.5V 5V 80mcd @ 10mA 60 625nm
Standard Yellow 30mA 2.1V 2.5V 5V 32mcd @ 10mA 60 590nm
Standard Green 25mA 2.2V 2.5V 5V 32mcd @ 10mA 60 565nm
High intensity Blue 30mA 4.5V 5.5V 5V 60mcd @ 20mA 50 430nm
Super bright Red 30mA 1.85V 2.5V 5V 500mcd @ 20mA 60 660nm
Low current Red 30mA 1.7V 2.0V 5V 5mcd @ 2mA 60 625nm
IF max. Maximum forward current, forward just means with the LED connected correctly.
VF typ. Typical forward voltage, VL in the LED resistor calculation.
This is about 2V, except for blue and white LEDs for which it is about 4V.
VF max. Maximum forward voltage.
VR max. Maximum reverse voltage
You can ignore this for LEDs connected the correct way round.
Luminous intensity Brightness of the LED at the given current, mcd = millicandela.
Viewing angle Standard LEDs have a viewing angle of 60, others emit a narrower beam of about 30.
Wavelength The peak wavelength of the light emitted, this determines the color of the LED.
nm = nanometer.
Pin connections of LED displays
 

There are many types of LED display and a supplier's catalogue should be consulted for the pin connections. Like many 7-segment displays, this example is available in two versions: Common Anode (SA) with all the LED anodes connected together and Common Cathode (SC) with all the cathodes connected together. Letters a-g refer to the 7 segments, A/C is the common anode or cathode as appropriate (on 2 pins). Note that some pins are not present (NP) but their position is still numbered.

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