Greetings,
I need electronic help :) As you will see, I am at my very early stage (like
some kernel...!)
I want to display a number on a digit (7-segment led), and I use a 74LS47
My digit is a "LTS-546AP" (common anode).
Here are the datasheets:
http://www.liteon.com.tw/OPTO/SPEC/DATABOOK.NSF/PASN/DS-30-98-055/$file/S546AP.pdf
http://dragon.herts.ac.uk/facilities/stores/datasheets/logic/ls/74LS47.pdf
a
+---+
f| g |b
+---+
e| |c
+---+ .
d dp
6 +-----+
g f A a b------\ /e -| |- GND (pin 8)
| | | | | | /d -| 7 |- A
--------- | /c -| 4 |- D
| _ | \----- /b -| L |- /RBI
| |_| | /a -| S |- /(BI|RBO)
| |_| | /g -| 4 |- /LT
| *| /f -| 7 |- C
--------- (pin 16) Vcc -| |- B (pin 1)
| | | | | +-----+
e d A c *
1 3
| (anode)
+5V
What I want to do:
- connect 74LS47 pin 16 (Vcc) and LTS546AP pin 3 (anode) to TS-7200 +5V (LCD
header)
- connect 74LS47 pin 8 (ground) to TS-7200 ground (LCD header)
- as partially drawn : pin a, b, c, d, e, f, g to 74LS47 /a, /b, /c, /d,
/e, /f,
/g
- connect 74LS47 pin 7, 1, 2 and 6 (A, B, C, D) to TS-7200 DIO header
pin 1, 3,
5 and 7 (DIO_08, DIO_09, DIO_10, DIO_11)
That sound too easy, my questions are :
- Should I need to put resistances between a,..,g => /a,...,/g, how
many, why ?
According to the datasheet, the 74LS47 can sink up to 15V. How many
current is
there on the pin /a when lit ?
- Should I need to put resistances between my DIO header and the 4
inputs A, B,
C, D ? My DIO can only source 4ma is that enough ?
In the datasheet I don't understand this line :
I = On-State Current /a to /g : 24ma <= ?????
O (on)
- I am confused with TTL input, sometimes I read it is 0-5V and
sometimes 0-3.3V ?
- Can I connect the ground (needed by the 74LS47) to the TS-7200 ground
(DIO header and not LCD header), is it the same ground ?
- In the 7-segment datasheet, I don't understand this line :
Peak Forward Current Per Segment : 60 mA
(1/10 Duty Cycle, 0.1ms Pulse Width)
If all segment are lit, I will need 7*60 = 420mA ? That's quite much ?
(read that the "5V power output pin on the LCD header has 750mA Poly-fuse
to prevent excessive current)
Thanks by advance !
Matthieu
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