4017 & 555 Police LED Lights Project (noob question - Page 1
Forum section: electronics / projects

author: 10101010
author_rank: Newbie
timestamp: February 19, 2015, 02:13:20 pm
content: hello, i am assigned to create a physical project starting from the schematics on the left side. my teacher told me that the schematic is incomplete, so the first step is to corect it and then use pads and then send the gerber files to a company to create it. i started reserching it and every schematics i found on the internet about this project had a major diffrence...in my schematics the outputs of the IC 4017 is conecte to 6 resistors...on a number of other similar schematics they are connected to 6 diodes...this is my first project and it is the first time i have to use my electronics knowledge to do something from a tp z and aparently i don`t have much of it...can some one please talk to me about the diffrences on those schematics...can any one shed some light for me on this subject? i will be forever gratefullthank you in advance(sorry for my bad english, i hope you understand what i am talking about ^.^)

author: DJohn
author_rank: Regular Contributor
timestamp: February 19, 2015, 03:11:23 pm
content: Before you design a board, wire it up on a breadboard first. If you're not 100% sure of the schematic, it'll be much easier to fix any problems there.The two circuits look like they're trying to do the same thing: three flashes of one light, then three flashes of the other, then repeat. But they work in slightly different ways.The second is the easier to understand. When an output of the 4017 is high, current will flow through the attached diode, through the resistor, and switch the transistor on. The other outputs are low, so current won't flow through their diodes, and they won't affect anything. If one of the unconnected outputs is high, nothing happens.The other one is a little different. When one output of the three is high and the others low, the resistors would normally give one third of the supply voltage. Current can flow through the base resistor and turn the transistor on. But there are also those two diodes. When the clock input to the 4017 is low, current will flow through the diodes, and the output of the resistor networks will be close to ground. When this happens, no current will flow to turn the transistor on.The first circuit gives a gap after lighting each LED: left, off, left, off, left, off, right, off, right, off, right, off, left, ... The second would need 12 outputs from the 4017 to do this, so it leaves out the gap when switching from out output to the other: left, off, left, off, left, right, off, right, off, right, left, ...I don't know what's incomplete about either schematic though. You should ask for more details. Or build it on a breadboard and if it doesn't work, investigate why.

author: Corporate666
author_rank: Unknown
timestamp: February 19, 2015, 03:33:44 pm
content: Quote from: 10101010 on February 19, 2015, 02:13:20 pmIs this really a school project? It seems strange that part of a school project would be to correct a bad schematic and send gerbers to a board house.Well, whatever... both schematics are from another site, here:http://www.electro-tech-online.com/threads/police-flasher-project.101163/page-2There is an interesting discussion (with some flaming) about the two different circuits and why one will work and one won't. If you are learning, then read through the discussion and follow along, it will show you where the error is in one of the circuits.

author: void_error
author_rank: Frequent Contributor
timestamp: February 19, 2015, 04:50:46 pm
content: The diodes + transistor in the second circuit form a 3-input NOR gate. R7,R8,R9,R10 can be increased at least 10 times, it'll work fine with 470 ohms and also waste a lot of power. The LEDs can be put in series, there's going to be enough voltage across them to light up. The series resistors may require some tweaking so the LEDs are at about the same brightness. You can also get rid of one more resistor by using the 555 like in the first circuit.Here's alinkto a simple java-based simulator, it'll help you understand how everything works for both your circuits.

author: 10101010
author_rank: Newbie
timestamp: February 20, 2015, 01:32:46 pm
content: nice. thank you all for the feedback it really helped. i think i figured it out. now i`m thinking to be a little arogant and add a speaker with the sirens of a police car, any toughts on that? i presume i need to make some major changes to the project but it`ll be worth it cuz i`ll stand out from the crowd .

author: 10101010
author_rank: Newbie
timestamp: February 20, 2015, 03:02:38 pm
content: so this seems an easy enough schematics...i just need to try and interpret it. if i do this more i`ll get good at it lol this is fun