555 with discrete components... - Page 1
Forum section: electronics / beginners

author: Unknown
author_rank: Unknown
timestamp: December 08, 2009, 06:22:36 pm
content: hi i want to know if someone can help me with this project...i want to build a 555 ( the classical timer ) with discrete components like resistances and transistors...but i cant find any good schematic description...for example this that i have found...https://sites.google.com/site/precisionaudiotv/_/rsrc/1244249588567/Home/aprendiendoplus/555_2.gifi think the schematic is all right but in the list of the description of components theres some confusion...for example...Q1 N5 5 N7 1 NPQ2 N1 6 N6 1 NPQ3 N1 N6 N8 1 NPQ4 N5 N7 N8 1 NPQ5 7 N16 1 1 NPQ6 N17 N14 1 1 NPQ7 N1 N1 N3 1 PNQ8 N17 N1 N2 1 PNQ9 1 N5 N2 1 PNQ10 N5 N5 N4 1 PNQ11 N11 N20 N9 1 PNR1 8 N3 4.7KR2 8 N2 830R3 8 N4 4.7KR4 8 N9 1KR5 8 5 5KR6 8 N22 6.8KQ13 1 2 N10 1 PNQ14 N14 N10 N11 1 PNQ15 N13 N12 N11 1 PNQ16 N13 N15 N12 1 PNR7 N14 1 100KR8 N13 1 100KR9 N15 5 5KR10 N15 1 5KR11 N8 1 10KQ17 N16 4 N18 1 PNQ18 N19 N17 1 1 NPR12 N18 N20 5KQ19 N20 N20 8 1 PNQ20 N21 N20 8 1 PNQ21 N21 N19 1 1 NPR13 N17 N21 4.7KQ22 8 N22 N23 1 NPQ23 N22 N21 N24 1 NPQ24 8 N23 3 1 NPR14 3 N23 3.9KQ25 3 N25 1 1 NPR15 N25 N24 220R16 1 N24 4.7KR17 N24 N16 10KD2 3 N22 DD1 N18 N19 D.MODEL NP NPN(BF=125 Cje=.5p Cjc=.5p Rb=500).MODEL PN LPNP(BF=25 Cje=.3p Cjc=1.5p Rb=250).MODEL D D(Is=1e-12 Cjo=1p Rs=5this is the list of components...how can i go to the electronics store and ask for this transistor???Q5 7 N16 1 1 NPMODEL NP NPN(BF=125 Cje=.5p Cjc=.5p Rb=500)with out to have to read a thousand pages of data sheet of every transistor that could be the one i look for...and the worst is that this is the best schematic that i could found...so if someone can help me telling me which are the models of these transistors and the diode...it will help a lot...or if someone can help with an other schematic it will be great...or anything that can solve this will help a lot...i really love the <3 555 <3please help me...

author: Simon
author_rank: Unknown
timestamp: December 08, 2009, 06:32:00 pm
content: Quote from: walterdelbono on December 08, 2009, 06:22:36 pmSimple answer is you won't find the schematic your after and no you can't build it just as simply as that. Whicle its a great project of reverse engirneering why do you want to do it ?your best bet is to take it one step at a time, the block diagram of a 555 is a window comparator, an SR latch and a discharge transistor. so you could use a dual comparator IC and a Latch ic and the neccesary external parts to make an equivalent.if you want to come down farther than that then find out how the comparator is built and how the SR latch is built.if your really fixed on this remember: its not about replicating the chip's diagram itself but building a descrete circuit that does the same thing so don't try to understand the "equivalent" diagram but how it works and design the solution to that.but again WHY

author: Unknown
author_rank: Unknown
timestamp: December 09, 2009, 05:00:53 am
content: because if i buid it i will learn a lot...and there's a very famous homework in my university for the more advanced students...i'm not advanced but i will be ...so i think it's good to build it now ...and in my country we are in holidays ...so i decided to start the project...thanks a lot for the help...when i start the project yesterday...jaja...i thought that if the schematic way doesn't work i should take way of making the logic gates by my self...because i want to make it all with discrete components...if some day i can build it i'm gonna put it in the wall of my room...jaja...thanks simon i will keep on working on it...

author: Unknown
author_rank: Unknown
timestamp: December 09, 2009, 05:18:37 am
content: Your list of components is not a list of parts to buy, it is a spice list for simulating the 555 function in something like Pspice.

author: Unknown
author_rank: Unknown
timestamp: December 09, 2009, 05:31:00 am
content: yes i get the schematic from a tutorial of spice...because it was the best schematic that i found...

author: Unknown
author_rank: Unknown
timestamp: December 09, 2009, 06:36:10 am
content: Sounds like a homework assignment. Do you need help with your homework?

author: Simon
author_rank: Unknown
timestamp: December 09, 2009, 07:58:25 am
content: you can't follow the spice schematic for biulding it from descrete components, like i said work from the block diagram not schematic diagram and build the blocks from descretes then you will have built a descrete 555

author: Zero999
author_rank: Super Contributor
timestamp: December 09, 2009, 10:57:48 am
content: You'll definitely learn a lot more by looking at the block digram and designing your solution to each sub-assembly than blindly building the internal schematic.The block diagram can be found using Google.

author: qno
author_rank: Frequent Contributor
timestamp: December 09, 2009, 11:15:02 am
content: Hi Walter,You can download the book of the inventor here.http://www.designinganalogchips.com/Good reading during the holiday's

author: Unknown
author_rank: Unknown
timestamp: December 10, 2009, 06:19:35 am
content: awesome book......thanks everybody for the help...

author: Simon
author_rank: Unknown
timestamp: December 26, 2009, 09:17:21 pm
content: so hows it going ?

author: jahonen
author_rank: Super Contributor
timestamp: December 29, 2009, 12:09:25 pm
content: Linear TechnologyLTspice IVhas discrete 555 example circuit in program installation directory, ...examples\Educational\NE555.asc. With that you can easily experiment with the circuit. I quickly tried changing the transistor models into BC847B (NPN ones) and BC857B (PNP ones), and the circuit still worked ok. I guess that just about any common small-signal transistor will do just fine. Although I'm not sure if there is a need for a matching the transistors. The matching is quite good between transistors in IC die.Anyway, like already said, there is not much sense about building the discrete 555 in another sense than just educational.Regards,Janne

author: Unknown
author_rank: Unknown
timestamp: February 26, 2011, 06:09:24 am
content: i found iiiiiiiiiiiiiiiit...http://www.ohmpie.com/hm555/

author: Simon
author_rank: Unknown
timestamp: February 26, 2011, 07:40:17 am
content: I never knew figuring it out was supposed to be so long winded, i mean the contents of the 555 is well documented

author: Lawsen
author_rank: Frequent Contributor
timestamp: March 23, 2011, 04:58:33 am
content: I can look it up in my electronics school era books. Like the rest of the group said, what is the purpose? It was my first experience with TTL oscillator with a square wave output and useful for function generator and TTL logic controls in home made robots. The timing is not as precise as a quartz oscillator or other standards. I do remember a schematic diagram on the data sheet in one of my books. You would be better off studying electronics for a projects book than trying to figure the insides of a 555 chip. The 555 chip is used in the switching power supply in the East German Aus Juna Zeiss Laboval 4 microscope. I love the high eyepoint eyepieces on it. The power supply is a hum sound. I like the quiet Olympus power supplies and the quiet Carl Zeiss KF-2. These are all entry level, lower end microscopes that I use in geology era. Old Zeiss Junior petrographic microscope has linear transformer power supply, that is absent of semiconductors. Newest microscopes have LED and electronic power supplies, which I cannot afford them. If I get some sleep and have time, then I will look for that schematic diagram in my books and post it on the gallery section. What is the purpose? I rather you buy a laser diode kit and build that and learn about that circuit than this.http://i-fiberoptics.com/lasers.php?cat=laser-kits&sum=1642Lawsen

author: saturation
author_rank: Super Contributor
timestamp: March 23, 2011, 12:22:02 pm
content: There is much to be gained by recreating someone's old work, mostly education in linear technique. Its the same way, many formal school curricula still ask students to recreate all the key theorems: Nyquist, Maxwell equations, small signal equations, etc., to be familiar with it as an exercise. Likewise, hobbyists and more, remake endless power supplies, amps, and function generators, what's the point? You can buy it cheaper than make it. Its for education, skill building.Now, try to make your own transistor. Gives you a new appreciation for something you can buy for 30c.http://blog.makezine.com/archive/2010/05/how-to-roll-your-own-nmos-transisto.html

author: neoone
author_rank: Regular Contributor
timestamp: March 23, 2011, 01:52:41 pm
content: I think it's a grat thing to reproduce such legends as 555 with discrete parts. I'll put it on my list of gadgets to make that serve no purpose other then being there and maybe to show of to my friends ;-)It would be even more interesting to make it using tubes ;-)BTW, home made transistors rules ;-)

author: the_raptor
author_rank: Regular Contributor
timestamp: March 23, 2011, 04:12:15 pm
content: Pfft making your own transistors? I saw a video of a guy the other day making his own tubes!

author: Lawsen
author_rank: Frequent Contributor
timestamp: March 24, 2011, 01:56:24 am
content: I have posted my report of inside the 555 in the schematic section of the gallery of this magnificent TTL astable multivibrator orginially by Signetics. I left out the R-S flip flop part of the circuit. Tim Williams has a great web site of the for building an R-S flip flop with discrete NPN transistors. There is a schematic diagram for vacuum tubes R-S flip flop, too. Surf here:http://webpages.charter.net/dawill/tmoranwms/Elec_Flipflop.htmlLawsen

author: neoone
author_rank: Regular Contributor
timestamp: March 24, 2011, 12:25:27 pm
content: Quote from: the_raptor on March 23, 2011, 04:12:15 pmThere was a guy on polish board elektroda.pl few years back who made tubes but I think it wasn't so sophisticated. Very nice indeed.Making 555 on tubes hmm, maybe after 10 different project that need to be finished (like Tesla coil for example) ;-) The costs of such circuit would be quite high though.