7 segments multiplexing

[colin mac]

If I want to multiplex four 7-segments displays, should I use PNP transistors or
NPN?

 

[Nigel Goodwin]

Depends on the polarity of the displays, but it's best to feed the displays from the collector of the transistors.

 

[geko]

If I want to multiplex four 7-segments displays, should I use PNP transistors or
NPN?

Either, depends how you do it.

Try this https://picprojects.org.uk/projects/counter/counter-sch.pdf

 

[colin mac]

Thanks, I'll try that Geko.

 

[superbrew]

When multiplexing displays, are the transistors required? I am running 3 displays using a PIC16F88 with no transistors, will this destroy the chip? Each segment is pulling about 1mA. They are common anode with the anodes driven by PORTA, and the cathodes on PORTB.

 

[Nigel Goodwin]

As long as you have suitable current limiting resistors in place, then it's no problem - but it's usual to use a transistor to feed each display, and drive the segments directly - in order to give a higher drive current.

My LED matrix tutorial feeds 64 LED's directly off two ports and works fine, and is plenty bright enough.

 

[superbrew]

Thanks. There is a 510 ohm resistor on each segment.

 

[Gayan Soyza]

I'm using high speed switching transistors when doing multiplexing in SSD.

I'm using common cathode type standard size SSDs.For the transistors mostly I use 2N 2222 ones.Collectors are driving the SSDs.

 

[X4ce]

well transistors are used for some purposes, like u need high current or external source to display ur displays, or if u have Common Anodes and ur program runs displays as common cathodes and u dont wana the change the program.

but u can run them without transistors as long as u have limiting resistors, these r needed even if u run with transistors.