Maxer

Hello this is the final Diagram, is there anything in wrong place or missing? Audio i also need to know what is the vaule are the resistors and capcitors in this diagram. I guess that might depend on the type of LED's i get i will provide the specs for those shortly. But just check this out if its correct.
Thank you
Max

Attached Images

lm3914_sequencer_317.jpg (56.6 KB, 1532 views)

jrz126

I dont think you need those current limiting resistors for the LED's.

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Maxer

why not? wouldn't the LEDD's burn out quick

JFDuval

Hi!

The LM3914 have internal resistances included. You have a pin to select the amount of current you want for the leds.

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Maxer

I want about 20mA to 25mA but nothing less then 20mA
what pin is it to select the resistances?
i am not good at electronics, i am a total beginner. The person who made this schematic for me is AUDIOGURU.... he give me value for the capacitor for 555timer and resistors.
here are specs for the LED's
Emitted Colour : WHITE
Size (mm) : 5mm T1 3/4
Lens Colour : Water Clear
Peak Wave Length (nm) : N/A
Forward Voltage (V) : 3.2 ~ 3.8
Reverse Current (uA) : <=30
Luminous Intensity Typ Iv (mcd) : Average in 10000
Life Rating : 100,000 Hours
Viewing Angle : 20 ~ 25 Degree

Absolute Maximum Ratings (Ta=25°C)

Max Power Dissipation : 80mw
Max Continuous Forward Current : 30mA
Max Peak Forward Current : 75mA
Reverse Voltage : 5~6V
Lead Soldering Temperature : 240°C (<5Sec)
Operating Temperature Range : -25°C ~ +85°C
Preservative Temperature Range : -30°C ~ +100°C
thanks
Max

jrz126

looking at the datasheet, it says that Iled is approx. equal to 12.5/R1 where R1 is your 620 ohm resistor. this comes out to about 20 mA

__________________
Jeff Zimmerman
To the optimist, the glass is half full.
To the pessimist, the glass is half empty.
To the engineer, the glass is twice as big as it needs to be.

JFDuval

Hi!

I can't tell you wich pin by heart but just read the datasheet and you will find your answer.

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JFDuval
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audioguru

Hi Guys,
Of course you need those current-limiting resistors. Without them, the LM3914 will be thermally stressed with 20mA thru 6 LEDS at the end of each scan, and a supply voltage of 14.4V. The chip's temperature will go from cool to very hot for each scan, which isn't good. The current-limiting resistors aren't needed for just "dot" mode.

Max, I am sorry that I didn't finish the 555 schematic, but its pin 7 (discharge) should be used to discharge the 1uF cap, not your diode from its output which does not go anywhere near ground.
I'll arrange it so that the discharge happens quickly then you won't see the LEDs run back down.

JFDuval

Hello!

I didn't saw the high voltage supply. Sry,

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Maxer

would that work? Should pin 7 be used, how much current can it take?
Does it depend on who makes the IC555?
and if it does what make should i use for this?
here is the updated

Attached Images

lm3914_sequencer_342.jpg (56.0 KB, 1409 views)

audioguru

Hi Max,
Good, now you have a circuit that will basically scan the LEDs linearly when the power is applied. Only a few adjustments are needed:
1) The 1st scan will begin with a delay before the scan (longer than remaining scans) as the cap in the 555 circuit charges up to its operating voltage level. I am still working on a solution.
2) The reset time needs to be shortened with a diode and resistor or just a diode for the 555 because now the reset time equals the scan time (it will scan for 1 second then be off for 1 second, then scan again etc.)

Don't worry about the 555's pin 7 ratings, it is normally used to discharge the 555's timing cap which could be huge and is very stong. National Semi has a note about it in their datasheet that says the only problem is if it causes the 555 to get too hot. It will not even get warm by occasionally discharging your puny 1uF cap. Here's what they say:

Note 7: No protaction against excessive pin 7 current is necessary providing the package dissipation rating will not be exceeded.

Maxer

To shorten reset time where would the resistor need to go and what value?

Maxer

or would this work..

Attached Images

untitled_1_486.png (3.9 KB, 1374 views)

audioguru

Hi Max,
That's a good idea that you have. There are many ways to connect a 555 but your newest one just might work well. It uses the 1uF cap and current source as the timing parts. The reset pin discharges the cap as fast as it can.
Its problem is that the LM3914's resistor divider between its pins 4 and 6 needs to be set to near the same voltage range as the divider in the 555. You can't simply connect them in parallel because the LM3914's divider resistance is too low. It would need to have its actual resistance measured with an ohmmeter then slightly lower value resistors added from pin 4 to ground and pin 6 to the positive supply. Like my attachment here.

The only problem remaining is the delay on the 1st scan. I am narrowing my search to 555 queries on another web-forum.

Attached Images

lm3914_s_divider.jpg (48.1 KB, 1349 views)

Maxer

hey AUdio thanks for helping once again..
Does it matter what company i get the LM3914 and 555 timer from? are they all identical?
i am getting all of my stuff from http://www.futurlec.com/cgi-bin/search/search.cgi
i am going to go ahead and order everything i need for 3 circuts.. 1 for practice and 2 for the real deal.. if you think would need anything else besides whats on the schematic please let me know
thank you
max