# Need help with a simple timer for flashing lights.

#### brendan3216

Joined Mar 9, 2016
7
Hi, my name's Brendan and I'm new to this site, but I need some help. I'm a highschool senior in the capstone couse of our engineering department. My friend and I are designing brake lights that show the intensity with which your are braking. On our display for our system, we want to wire some blinkers for display purposes. We have two store bought brake lights that we want to power at 12V. We want to have a timer pulsing a square wave signal to the blinker lights, and a toggle switch in series with each light so we can turn the blinkers on and off independently. The problem lies in the timer. Last year's engineering course covered the basics of electronics and circuits, and our physics classes have given us a basic understanding of the principles involved in building circuits, but I'm lost. We have 555 timer chips and access to AOI chips. We also have proficient knowledge of how to convert AOI circuits to NAND-NOR circuits. I don't know what resistance our lights give, or what current our power supply outputs. I need help asap, if possible. We're coming up on the deadline or our project, and this is one hurdle I can't figure out. Thanks so much for your help!

#### blocco a spirale

Joined Jun 18, 2008
1,546
How do you measure braking intensity?

#### brendan3216

Joined Mar 9, 2016
7
Through a mechanical system of perpendicular connections. I'll explain more in depth if I'm able to get this blinker system up and running.

#### brendan3216

Joined Mar 9, 2016
7
And I would like to clarify that this is in no way going on an actual car, it just needs to represent blinkers on a piece of plywood.

#### blocco a spirale

Joined Jun 18, 2008
1,546
Let me try it a different way; how do the brake lights respond to different braking intensities?

#### brendan3216

Joined Mar 9, 2016
7
As you press on the pedal, the motion is transferred through a bowden cable to a 3d printed plunger system, where there is a live wire running down the male end, and many wires running perpendicularly in the female end. Each connection made in the female end lights up a row of led's in the brake light. We have that figured out for now. What I REALLY need help with is figuring out this timer system.

#### blocco a spirale

Joined Jun 18, 2008
1,546
Last edited:

#### brendan3216

Joined Mar 9, 2016
7
That looks excellent, thank you! I do have two questions though. I'm not sure what either of these symbols are and I'm assuming the 100K by that first symbol means 100 ohms? Thanks in advance!

#### blocco a spirale

Joined Jun 18, 2008
1,546
Surprisingly, 100k means 100kΩ and if you google "2N3055" ........

#### brendan3216

Joined Mar 9, 2016
7
Alright, cool. Now, is that just a normal 100K ohm reistor, or is it different somehow? It looks different. And I found the 2n3055. Looks like I'll have to order it online. If I'm going to order something online, would it be easier just to order a pre-made circuit that did this if such a thing exists? Preferably something I don't have to program (not an arduino or raspberry pi), and something I can leave on for extended periods of time with no start up or shut down sequence. If not, I'll order the 2n3055 and hope this works. Thanks again!

#### Bernard

Joined Aug 7, 2008
5,784
Do you have any electronic parts store or a Radio Shack available? Ask for a NPN power transistor @ around 5 A, or N channel FET @ 5A.

#### blocco a spirale

Joined Jun 18, 2008
1,546
Alright, cool. Now, is that just a normal 100K ohm reistor, or is it different somehow? It looks different.
It is a preset potentiometer.

#### djsfantasi

Joined Apr 11, 2010
9,131
I agree. Also known as a trimmer pot. It is the same as a regular pot, but wired as a variable resistor. Not a pot with a large knob, but set with a screwdriver and not meant to be changed. Without seeing the rest of the diagram, I surmise that it is used to set the timer frequency.

#### Alec_t

Joined Sep 17, 2013
14,012
I don't know what resistance our lights give, or what current our power supply outputs.
That's something you need to find out.

#### TheButtonThief

Joined Feb 26, 2011
237
As you press on the pedal, the motion is transferred through a bowden cable to a 3d printed plunger system, where there is a live wire running down the male end, and many wires running perpendicularly in the female end. Each connection made in the female end lights up a row of led's in the brake light.
The device you describe is an indexer, mechanical in nature.

#### bertz

Joined Nov 11, 2013
327
That looks excellent, thank you! I do have two questions though. I'm not sure what either of these symbols areView attachment 102216 View attachment 102217 and I'm assuming the 100K by that first symbol means 100 ohms? Thanks in advance!
Hi Brendan,
It is obvious that you are totally inexperienced in the art of reading schematic diagrams. Let's start with reading schematic diagrams. Here is a nice little crib sheet that will give you the key for reading schematic diagrams.

http://www.rapidtables.com/electric/electrical_symbols.htm

Going back to the referenced schematic, you will recall that the component you were having a problem with is labeled VR1. The VR stands for variable resistor. You will also note that it has a value of 100k. So what does 100k mean. Well we know that the units for resistance are ohms, and the suffix k means 1000. Therefore the value of VR1 is 100,000 ohms. That was easy to explain, wasn't it.

I note that the oscillator is based on a 555 chip so I would suspect that you will be building the circuit on a perf board of some kind. If you don't know what a perf board is, google it. You have to put some sweat equity into this project. So you will want to buy a variable resistor that will mount readily into a perf board. Here are some examples:

Check out this website for all sorts of electronic components and data sheets. Never attempt to build an electronic circuit without data sheets for the main components.

http://www.digikey.com/product-deta...rth-america/PV36W104C01B00/490-2876-ND/666503

Good luck!