Thanks for your answer Keith.
So, You're right, the TS-7200 DIO header is in fact LV TTL (3.3V)
(Low-Voltage Transistor Transistor Logic).
I have found something good :
http://www.interfacebus.com/voltage_LV_threshold.html
If everything is true, I can safely connect LV TTL output to my 74LS47
TTL input
Concerning resistors (outputs of 74LS47), I don't understand:
The output pin (/a, ..., /g) are sinking current, so the current go from
the LED to an output pin :
5V -->---[LED|>]---->--- pin /a
So this resistor (located after the LED) won't affect the lighting power
of the LED, it's just for limiting the current entering inside 74LS47,
am I right ?
About voltage, how to know how many volts have we in pin /a; is 15V enough ?
V Off-State Output Voltage /a to /g : 15V
O (off)
I On-State Output Current /a to /g : 24mA
O (on)
Matthieu
Keith Gilman wrote:
>--- In Matthieu Crapet <> wrote:
>
>
>>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/74LS4
>7.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
>>
>>
>>
>
>Matthieu,
>
>I'll try to answer some of your questions starting from the last.
>
>1) The peak forward current is the maximum you can apply to the LED
>with a 10% duty cycle. The current you will need is probably much
>lower than this. Typically on the newer LEDs you will only need to
>drive it at about 10 mAmps per segment.
>
>2) The grounds are the same.
>
>3) The TTL levels depend on which logic family you are using. 5v TTL
>levels are not the same as 3v TTL levels. I'm not an electronics
>engineer so what I would do is just try it. As long as you don't
>connect a 5v logic output to the TS-7200 inputs you should be OK
>(although I can't guarantee it will work :-)
>
>4) The output lines from the TS-7200 should be able to drive the
>inputs to the 74LS47 (A, B, C, and D).
>
>5) Yes you WILL need to add resistors from the outputs of the 74LS47
>to the LED segments. This is what sets the current for each segment.
>You may need to try different resistance values to get the
>brightness you need. I would start with 470 ohm resistors giving a
>current of about 10 milliamps. If all segments were lit you would
>then be drawing 70 milliamps.
>
>6) Everything looks ok to me. The only concern I have is can the 3.3
>volt logic levels drive the 74LS47 (you won't need resistors on
>those data lines). Since the LCD port is used to drive LCDs with a
>5v logic input I would assume that it will work.
>
>Good luck. Hope I answered some of your questions.
>
>-Keith
>
>
>
>
>
>
>
>
>Yahoo! Groups Links
>
>
>
>
>
>
>
>
>
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