is resistor necessary for driving 7Segment?

[Hesam Kamalan]

Hi,

i used latch to keeping data of 7segment. is resistor(about 330 Ohm) necessary between latch and 7segment?

 

[blueroomelectronics]

Generally yes you need a resistor, they're pretty cheap.

 

[lord loh.]

I would recommend using 8 resistors rather than one on the common pin. Some segments have a low dynamic resistance that makes it glow very bright stealing current away from the other pins and hence causing them to glow dull.

 

[Gayan Soyza]

Yes,My favorite values vary between 120R-220R. 330 Ohm pretty bit high.For one segment its ok, but for multiplexing 4 or above it needs a lower value otherwise the display will dim.

 

[Hesam Kamalan]

Thank you dears,

in my project i employed 14 latch and 7segment. i want to use resistor array for each latch and 7segment (in addition 14 resistor array). is it good idea?

 

[Hesam Kamalan]

if it's possible, download this block diagram and tell me your thought, please.
https://www.electro-tech-online.com/custompdfs/2008/05/Digital20Watch20Sch.pdf

is it good circuit?

**broken link removed**

 

[blueroomelectronics]

It's an awful lot of parts, I would recommend a much simpler design but would take slightly more I/O pins and would be a 1/8 mux (refreshed) display not a latched display. Treat the segments A-G & d.p. as row drivers and turn on all 14 digits at once but only one segment at a time. A SN74HC138 could act as a 3 to 8 decoder for the rows, you'll need driving transistors that can handle sinking or sourcing the entire 14 segments at once and you'll only need 14 current limiting resistors on the CC or CA pins of the digits.
Take a look at my Dragonfly kit for ideas.
**broken link removed**

 

[lord loh.]

I prefer to use serial shift resisters. These take less pins and can be cascaded to connect several 7 segs.

 

[carmusic]

if it's possible, download this block diagram and tell me your thought, please.
https://www.electro-tech-online.com/custompdfs/2008/05/Digital20Watch20Sch-1.pdf

is it good circuit?

**broken link removed**

You only needs the 16f877 and program the seven segement on it and three transistor to drive sequentially the 7segment, no needs for decoder and latch.
i currently do it with 5 number at a refresh of 500hz and it is ok