Need help/advise

[RAA]

Hi i am building a lil thing for my gf it's nothing complex i wrote her name in leds and wired them threw a 74190 in a way that well who cares what way they light up anyways i used 55 leds (leds in each letter vary from 9 to 12) i will be using a 9v pile as a vcc source but i a concerned about the courent coz all leds r wired paralell so that means i have no problem with voltage but i think the courant should be amplified or mabe not right now i have the outputs directly wired to the leds but i need to know do i need to wire them 1st threw transistors in order to amplifie?? if yes can some1 tell me what to use and how to use it :roll:

by the way i am wondering if i make this circuit compatible with 220v instead of the 9v would i still have current issues? the only reason i dont like the idea of 220v is that even tho sometimes she pisses me off but still i dont want to electrecute her.... yet :lol:

 

[evandude]

I doubt that a logic chip could drive 55 LED's by itself, so you would need to use a transistor. However, since you were so vague about your connection, it's hard to give you a circuit diagram for it.

How many LED's do you have connected to each output of the chip? and are the LED's all exactly the same, or are they different colors/sizes/brands? (it's generally easier to drive LED's if they are all identical...)

if each output only needs to drive 10 or so LED's then you can tie the anodes of the LED's to your +9v rail and use an NPN or NMOS transistor to pull the cathodes to ground. Here's where the LED types come into play. if they are all identical, you can probably connect all the cathodes for each group of LED's together and use one series current-limiting resistor between the cathodes and the transistor. if they aren't all the same, you would most likely have to use one resistor for each LED.

 

[Roboticinfo]

reply

Do you know how to use a microcontroller?

 

[audioguru]

9 to 12 LEDs in parallel will draw about 100mA which is far too high for a little 9V battery.
A red LED is about 1.8V. Therefore from a 9V battery 7.2V will be wasted across the current-limiting resistor. If you connect the 1.8V LEDs in series groups of three or four in each group, they will look and operate the same but draw only 33mA or 25mA.
Even only 25mA is far too high for a 74190 to drive, so transistors must be used at the 74190's outputs.

You didn't mention a clock oscillator to drive the 74190 nor a 5V regulator for them.

You don't connect low voltage circuits directly to the 220V mains, you use a voltage adapter with a transformer, rectifier and filter capacitor inside. Its output voltage and current ratings must be enough for your circuit.

 

[RAA]

ok the circuit is as folowing there is the NE555 clocking at F=1Hz the 74190 and the 74190's output id wired to a 7442 decoder and from that decoder i have 5 outputs for the 5 letters i did.. i'm sure before letting those output go to the led they should go threw amplification but how? and hould would this amplification connection look like? thats my question
about paralell or serial i alredy did the led circuit paralell so no turning back to serial so my question is "what do i do to make that output of the 7442 wich is powerd by 9v go to a max of 12 leds in paralell connection"

 

[audioguru]

Hi RAA,
The old 74xx series hasn't been produced by many manufacturers for years so I had a hard time finding their datasheets.
You don't say anything about a 5V voltage regulator for those old IC's. They will burnout with a 9V supply.

Each LED has a slightly different voltage, so when they are in parallel, their brightness will all be different. It might be so different that one LED will hog all the current and burnout. Then the rest will burnout one-at-a-time because the current for only a few will be too high. Are you feeling lucky that they all might be the same? :lol:

The current in so many LEDs will kill a little 9V battery in a short time. Plus the high operating current of the old 74xx IC's. You are going to need an AC to 9VDC adapter for power.

But anyway, you could use 2N3906 PNP transistors to drive each group of paralleled LEDs in series with a current-limiting resistor. Connect the transistor's emitter to the positive battery terminal, its collector to the current-limiting resistor, the other end of the resistor to the anodes of the LEDs and the cathodes of the LEDs to ground. The base of each transistor should have a 4.7k resistor in series that is driven by the output of the 7442.

The 1st time you try it use a current-limiting resistor for a single group of LEDs of 270 ohms 1/4W. If all the LEDs in the group are about the same brightness (very dim) without a bright one, add another 270 ohm resistor in parallel with the 1st one and try again. If all LEDs are the same, you can use five 270 ohm 1/4W resistors in parallel for 12 LEDs, or four 270 ohm 1/4W resistors in parallel for 9 LEDs.
Then try the single 270 ohm resistor and parallel more again with every other group of paralleled LEDs.

Next time, think about the theory stuff before the wiring stuff. :lol:

 

[evandude]

Next time, think about the theory stuff before the wiring stuff. :lol:

I agree :wink:

 

[RAA]

hehe yea i forgot to mention i'm using the 7805 regulator to transforme 9 to 5 volts
well in the amplification what if i use bc141 transistor it suports hight current well with a 1k resistor at the base and 2.2k on the collecter with the emeter wired to the ground that would do the trick no?

i'm just wondering if i use an 220v AC to 5V DV what whould that do? other then of course save 9v pile consumption thus some money? i mean other then that will it salve my "current" problem? or still i would need the transistors?

Next time, think about the theory stuff before the wiring stuff.

hehe that would help but at the time i had the idea i was thinking less of the technical stuff and more of the effects on the girl

 

[audioguru]

Hi Raa,
A 7805 is guaranteed to regulate well with an input voltage of 8V or more. Your little 9V battery will drop to below 8V in an instant and still should power things when its voltage is only 6V. I use low-dropout regulators with 9V battery powered projects because they are guaranteed to regulate well whith an input voltage of 5.6V or more.

If you use BC141 NPN transistors, the LEDs will be on when they should be off. You need a PNP transistor wired as I posted before. I don't know what good a 2.2k collector resistor will do.

I don't know what is a "220V AC to 5V DV". If it is an unregulated adapter, its voltage will rise to 7V or more when the LEDs are off and fry your 74xx IC's. I have seen many adapters double their output voltage when not fully loaded.

He, he. My wifey says that guys like me can do only one thing at a time, while girls like her can do many. She hasn't noticed me looking at the hot teen girls in their bikinis next door while I am typing this! :lol: :lol:

Even though you have the girl on your mind all the time like most of us guys, you must learn to concentrate on other things too. I had a young pretty secretary with a very short mini-skirt ......., I somehow got my work correctly done! :lol: :lol:

 

[JimB]

Sounds like too many LEDs to me.

Try finding a girlfriend with a shorter name!

Any pretty girlies called . in your area?

JimB

 

[audioguru]

Hi Jim,
Dot is a short form for Dorothy, isn't it?
I have seen dogs named, Spot. Why aren't pretty girls named, Spot?
I like their spot. He, he. :lol: :lol:

 

[Nigel Goodwin]

Dot is a short form for Dorothy, isn't it?

Yes it is, my wife has an Auntie Dot :lol:

For a really, really sad story, Dot's daughter died the other year, she was only in her twenties, and an absolutely stunningly beautiful girl. She had only been married for a short time and was diagnosed with cancer, she died not many weeks after it was dianosed :cry: :cry:

 

[eblc1388]

 

[mstechca]

Raa,

Here's what you need to know.

LED's in parallel are OK, but having too many of them in parallel (especially if they have extra low resistance) will drain batteries very quickly.

LED's in series are also OK, but the brightness will not be at maximum because the resistance (LED's) is in series.

I think the ultimate solution is to use a low power counter which turns on a few of your 55 LED's at a time, at a high enough speed, that even a human can't tell that the LED's are switching. A speed of at least 1Khz would probably do.

 

[audioguru]

LED's in parallel are OK

Not necessarily. They are OK only if you test them and match their forward voltage drop. Otherwise the one with the lowest voltage will be bright and the rest will be dim or not even lighted.

LED's in series are also OK, but the brightness will not be at maximum because the resistance (LED's) is in series.

Definitely not! You can choose any brightness you want with a properly chosen current-limiting resistor. LEDs don't have a resistance, they have a forward voltage drop like any other diode. Of course you must have enough voltage for the LEDs and current-limiting resistor. :lol:

 

[RAA]

i think i found a reasonable solution i will make series and wire them in paralell i was thinking mabe 6 leds per serie maz of cours even tho this is easy wiring but i would need about 14 volts to get good result but i will only have 5v output from the decoder so i should wire the 14v on the leds and inver the output of the decoder that should work no?

 

[audioguru]

Hi Raa,
You haven't said which LEDs you're using but if they are 2V max ones, then 6 in series plus a current-limiting resistor for them can be driven by a PNP transistor as an inverter powered by a 14V supply. The transistor can easily drive 2 series strings like this for your total of 12 LEDs per output of the 7442 decoder.

I can't remember the high output voltage from a 7442 but it must be about 3.5V to 4.0V. Therefore a level-shifter can be made with a couple of resistors plus a zener diode.

The 14V supply is also adequate to power the 7805 regulator. Since the output voltage swing of the 7442 is so small, the 14V supply might need regulation to allow the level-shifters to work properly.

The circuit would be a lot simpler and use much less current if you use Cmos logic IC's instead of old TTL. Does any company make a 74190 anymore? TI doesn't and don't list a 7442 on their website anymore. The two TTL IC's alone will draw a typical operating current of 93mA! Cmos draws nearly nuthin and works directly from 14V without any regulators. Also with Cmos, level-shifters wouldn't be required. :lol:

 

[RAA]

ok then i will replace the TTL's with CMOS coz as u said why complicate things when u can simplify but i didnt get the part about the wiring threw the pnp transistor but i think what will not be an issue with cmos no? coz if it takes input of 14 that means output is what 13? 12? and using regular red led (1.7v) i would need 12.74v to make then work properly if thats the case mabe 15v better then 14v is that analogie correct? but the only thing i know about cmos is that they have working range from 5 to 15v

if my analogie is correct then again the only remaining problem is with the current since i need about 18ma for the led to work since i will have 2 strings of 6 led wired paralell meaning i need at least 36 well lets say 40ma will the output of the cmos decoder handle that? or there is no way to salve the current issue without transistors?

(by the way sorry if i'm beeing a pain in the ass or something :roll: )

 

[audioguru]

Hi "Pain in the ass". He, he. :lol:
Many manufacturers today rate their Cmos IC's with an absolute max supply voltage of 20V or 22V. Older ones were 18V. So 15V is fine.

For your circuit I would use a two-gate or two-inverter "classic" Cmos oscllator and a CD4017B stepper whose 10-steps sequence can be shortened by connecting the next output to its reset pin. For LED drivers I would use a CD4049UB hex (6) buffer that with a 15V supply can output typically 60mA with a 2V drop. Since the buffer has a voltage drop, the value of the LED current-limiting resistors will be lower than you think. :lol: