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Author Topic: PWM with 555 for 30 leds 12v  (Read 7267 times)

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p4ntb0y

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PWM with 555 for 30 leds 12v
« on: August 12, 2011, 18:58:46 PM »
Hi,

I have been trying to replicate the Pwm Led Dimmer as per
http://pcbheaven.com/circuitpages/LED_PWM_Dimmer/

I have tried to read up on everything but I have lots to learn  :(

I have a 12v supply and I would like to power 30 Leds Green I am not sure of the voltage of these But I think its 3.2 20Ma. so I work out that I will draw about 200Ma I think.

Now the Hard bit Its very hard for me to find the parts as I am in Japan and I am English so its a nightmare trying to translate and explain.

Parts I have are.....

LMC555CN
R1 4.7KOhm
R2 10k Pot
C1 0.1uf blue cap Tried to explain ceramic failed badly  >:( does this need to be ceramic?
D1-D2 1N4148 switching diode

T1 well I cant get a 2N2222 I asked the guy for one that will do the same job and he just looked blank.

I have
C2542
K30A
C2655
C1815
A1015

Any help would be great.

I am sorry if this is really noobish question  ;)

kam

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Re: PWM with 555 for 30 leds 12v
« Reply #1 on: August 12, 2011, 23:11:22 PM »
first of all, one question: how is it living in japan? Is it like we see in TV, a world full of gadgets and people with green and purple hair??? An what about the radiation? How has affect the life of Japan?

the capacitor is not necessary to be ceramic, although i suppose the one you got is ceramic. For the 30 LEDs with 12 volts supply, you will follow the 47 ohms resistor (you could use a smaller one as well if you want brighter LEDs). You need to have 10 rows, each one with one resistor and 3 LEDs. Each row will draw max 20mA, so you are right, 200mA is the max current.

Regarding the transistor, you could use any other transistor capable to power 200mA (AT LEAST 200mA). The ones you propose i have never heard of... ever! So i tried to find the datasheets. I found for:
C2542 - no datasheet found
K30A - no datasheet
C2655 - 1A. current is ok, hFE around 40: hmmm you may need to use smaller R1, like 2K2
C1815 - 120mA (no good)
A1015 - 150mA (kid's play)

So, go for the mighty C2655 with smaller R1, as you need lot of current for the LEDs. Here is a rough calculation for R1:

You need 200mA current, let me say that you could use 250mA. The transistor hFE is 40, so the base current must be 200/40 = 5mA

The base supply is 12 volts and you need 5mA. So, the minimum resistor you can use is (ohm's law):

R=U/I => R=12/5 = 2400 ohms. Close to this value is 2.2 kOhms (also we write as 2K2).


p4ntb0y

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Re: PWM with 555 for 30 leds 12v
« Reply #2 on: August 13, 2011, 07:10:35 AM »
Its great in Japan Girls are nice  ;) but I may be becoming a bit of an otaku as I turned a date down to do this circuit!

Its not like on the TV most people here dont know how to use a computer properly you do get clever people the geeks *Otaku*

As for the gadgets yeah its good  :) internet as well my mobile has 42Mbps internet and at home I have 100mbps fibre although this is starting to feel a bit slow... I rememberer my good old 56k playing counterstrike happy days. Now I can upload 20mbps and downloading big files is a breeze. cheap as well.

I live in Osaka pretty far from Fukishima so everything is normal here everyone is trying to save electric  :)

Thankyou for explaining that to me makes more sense now esp with the calcs  :D

so if If I ramp it up to 400Ma I need R=12/10  =1.2 KOhms

If I want more leds I dont by the way I can go all the way to 1amp if I wanted more I could spilt the leds across multiple C2655 s is the right ?

I just went out and bought some pic.s and a pickit 3 I want to make a 20 channel PWM controller for a sign is this hard to do? but thats for another day  ;)

Thank you for your time  :D

kam

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Re: PWM with 555 for 30 leds 12v
« Reply #3 on: August 13, 2011, 13:03:29 PM »
what is the "otaku" thing ?????  ::) ::) ::) ::) :-\ :-\ :-\
100Mbps..... 100 mbps!!!!! A HUNDRED!!!!  :o :o :o :o :o :o :o :o :o :o :o :o :o :o :o ten times faster than mine, which is BTW the faster i can get here. Damn.

You can add multiple transistors to have more LEDs. Each transistor must have its own resistor. The maximum number of transistors you can add has to do with tme max current that the 555 can sink. If you load each transistor with 1 amp, you need for each one 1.2 KOhm resistor. I would go down to 1Kohm. So, each transistor adds 12/1000 =  12mA (I=U/R) current to the 555 pin. Check the max current it can sink and calculate how many transistor you can add.

How much did you bought the PICKIT 3? A friend of mine (pike) just bought a clone. You bought the original pickit 3 from microchip or a clone?

What you want to make with the PIC is not hard, but if you know jack about programming then it is impossible. You first need to learn how to program a microcontroller. If you have enough time, patience and will, you will learn enough to make it in a few weeks.
Which PICs you got?


_pike

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Re: PWM with 555 for 30 leds 12v
« Reply #4 on: August 13, 2011, 18:09:38 PM »

I just went out and bought some pic.s and a pickit 3 I want to make a 20 channel PWM controller for a sign is this hard to do? but thats for another day  ;)

Hello!.Which pics did you buy?Did you look if the pics have the requierments that you need?As i have said to other people whether you are rookie or not take a look here .....   http://pcbheaven.com/picpages/    is the best pic tutorial that i have read (if you are intrested in assembly language programming) and also you can ask for help here......  http://pcbheaven.com/forum/index.php/board,29.0.html  Kam has made an excellent job and he is also very good programmer. We will certainly help you if someone of us can....As my teacher (Kam) say knowledge must be free and when you say something you know to other people,you learn it better..... ;)


p4ntb0y

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Re: PWM with 555 for 30 leds 12v
« Reply #5 on: August 14, 2011, 08:36:19 AM »
Many Thanks!

I will do a new post for my pic stuff  :)

I paid 6500 yen for my pickit 3 from a shop in denden town an electronics area in osaka

PICS i have PIC16F628A-I/P, PIC16F819-I/P I have a few different ones but not checked yet as I need to get my dimmer working first  >:(
I am happy doing proggy work  ;)

Ok what I am doing wrong pic attached

I picked up a 2SA1941 this puppy can handle 10a its a bit overkill  :(

please feel free to internet slap me if I done something simple!


_pike

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Re: PWM with 555 for 30 leds 12v
« Reply #6 on: August 14, 2011, 17:29:17 PM »

I paid 6500 yen for my pickit 3 from a shop in denden town an electronics area in osaka


OH MY GOD!!!!!!!!!! 6500 yen????????????? The conversion to euro is 60!!!!! Too expensive... at least hope that you have purchased the original and not a clone.....Two days ago i bought the pickit3 (clone) for 25 euros with 3 universal zif board, in case that you don't want to use the icsp connector and you would like to programm it "on the fly"...... The programmer i was using was the pickit2 but i had built it myself.(now all chips are supported by pickit3 so had to buy this programmer for newer chips...)

p4ntb0y

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Re: PWM with 555 for 30 leds 12v
« Reply #7 on: August 15, 2011, 04:12:02 AM »
Yeah Yen Is strong I am rich!

Its a real one

I worked out my circuit

it was the C2542 the pins are different
Its ok I learnt alot with this circuit

now I done this its time to  play with the PICS

Ahh yes I need to build an icsp board now

Where did buy yours pike?




_pike

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Re: PWM with 555 for 30 leds 12v
« Reply #8 on: August 15, 2011, 10:10:33 AM »
I bought this one.....
http://www.ebay.co.uk/itm/PICKIT-3-MCU-Universal-ZIF-socket-PICkit-2-3-/350484077399?pt=UK_BOI_Electrical_Components_Supplies_ET&hash=item519a7a9b57

but you can buy it seperately

http://www.ebay.co.uk/itm/MCU-Universal-ZIF-socket-use-PICkit-2-PICkit3-ICD-/110729004698?pt=LH_DefaultDomain_0&hash=item19c7f6869a

Also remember you don't need this.....you can take small wires and connect the output of the icsp directly to the appropriate pin
for example the vss from programmer's icsp to vss pin of the mcu and so on....


p4ntb0y

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Re: PWM with 555 for 30 leds 12v
« Reply #9 on: September 17, 2011, 14:18:36 PM »
Ok I am back a couple of questions.

I built this circuit and it latest about a week and I guess it burnt out.

The 555 ic chip gets hot is this normal?


I have all my leds wired in series of three on a 47Ohm resister so if i want to get rid of the pwm do i have to change the resisters for 120Ohms? or can i plug 12v to the 47ohm without worrying about burning them out?


kam

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Re: PWM with 555 for 30 leds 12v
« Reply #10 on: November 15, 2011, 19:36:08 PM »
555 must not get hot. bad news


Normally, 3 LEDs in series have a total voltage drop of 9.6V (3x3.2) at 30mA. You need to drop another 2.4V at 30mA, so you need a 80Ohms resistor in series (2.4/30).