How to design a ciruit that has 2 LED Lights

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Discussion Overview

The discussion revolves around designing a circuit that incorporates two LED lights that flash on and off while producing sound, resembling a police siren, all housed within a toy car. Participants explore various circuit designs, components, and configurations suitable for a beginner-level project.

Discussion Character

  • Exploratory
  • Technical explanation
  • Homework-related
  • Debate/contested

Main Points Raised

  • One participant expresses a desire to create a circuit with two flashing LEDs and sound, seeking guidance as a beginner.
  • Another participant suggests using a 555 integrated circuit for the LED flashing and sound generation, providing specific resistor and capacitor values to achieve desired frequencies.
  • A question is raised about the feasibility of integrating all components into a single circuit, specifically regarding the placement of resistors and speakers.
  • It is mentioned that a 556 chip, which contains two 555 timers, could be used, but concerns are raised about its cost and complexity compared to using two separate 555 chips.
  • Some participants discuss the need for multiple timers to achieve alternating tones for the siren effect, with one timer dedicated to the lights and others for the sound.
  • One participant suggests that pin 5 of a 555 timer allows for frequency modulation to produce two tones, and experimentation with resistor values is encouraged to optimize sound quality.
  • Clarifications are provided regarding the meaning of "uF" as microfarads, a unit of capacitance, and the importance of using appropriate resistor values for sound output.
  • Another participant shares their practical experience of testing the circuit on a breadboard, adjusting resistor values to improve sound quality.

Areas of Agreement / Disagreement

Participants express varying opinions on the best approach to design the circuit, with some favoring the use of two 555 timers while others suggest a 556 chip. There is no consensus on the optimal configuration or component values, and the discussion remains exploratory with multiple competing views.

Contextual Notes

Participants highlight the need for specific resistor and capacitor values to achieve desired flashing and sound frequencies, but there are unresolved questions about the exact configuration and component choices. The discussion reflects a range of assumptions about the participants' familiarity with electronics.

Who May Find This Useful

This discussion may be useful for amateur electronics enthusiasts, hobbyists interested in circuit design, and individuals looking to create simple electronic projects involving LEDs and sound.

Muhammad1993
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How to design a ciruit that has 2 LED Lights ...

I want to design a circuit for the sake of me seing if i can do it. I need the following things 2 LED Lights which are flashing on and off and make noise relative to when there on or off ( like a police siren ) and also i need to house all of this in a toy car which i am going to put a motor in and make it go forward. I am a total amateur so please if anyone can tell me how to do this it would be very much appreciated.
 
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You could start with something like this:

[URL]http://freecircuitdiagram.com/wp-content/uploads/2009/05/led-flasher-555.gif[/URL]

This uses a 555 integrated circuit which is available at almost any electronics supply store.

Notice that R1 and R2 are not given. They control the flash rate of the LEDS.

Try 10 K for R1 and 100 K for R2. This will give a flash rate of 1.5 seconds with each LED being on for half this time.
Making a sound could use a similar circuit with the top LED and R3 removed and the speaker connected instead of LED2. Make R4 47 ohms.

You would also need to change the resistors to 1 K for R1 and 10 K for R2 and change the capacitor to 0.1uF. This gives a frequency of about 600 Hz.

These can be changed but try to keep the resistors in the same 10 to 1 ratio.

Making the frequency of the second oscillator depend on the flashing rate of the first one would be done by connecting a 100 K resistor from pin 3 of the first chip to pin 5 of the second one.

This resistor can be changed to get more or less shift in frequency.
 
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is it possible to make all of this in one circuit, would it work if i kept R3 and LED1 and then put in another resistor which would be R5 and then a speaker after that ? if it is where would this go ?

Thanks for the reply btw
 


It is possible to get a chip that has two 555's in it. This is called a 556. It has different pin connections, of course.

However, the 555 is used so often that the 556 may cost more than two 555's.

The two 555s in this circuit operate at very different frequencies. The LED flasher operates at about 0.6 Hz while the sound maker operates at about 600 Hz, so you couldn't really get one 555 to do both of these jobs.

An alternative would be to use a Picaxe microprocessor chip. These are wonderful, but not available easily in all countries.
 


im sorry about this but I am a complete amatuer your going to have to explain it in a simplified way

would it be best to get one 556 or two 555's ? and the second of the 555 would go between after the R3 and R4 slightly after where the resistors are? and then they would connect to the speakers ?
 


Muhammad1993 said:
im sorry about this but I am a complete amatuer your going to have to explain it in a simplified way

would it be best to get one 556 or two 555's ? and the second of the 555 would go between after the R3 and R4 slightly after where the resistors are? and then they would connect to the speakers ?
Depending on what you want, you may need 3, unless there's a novel solution that I'm unaware of. (Which is very possible)

Since you mention a siren, my assumption is that you want it to alternate between two different tones (wee woo wee woo wee woo) in sync with the flashing lights. Is that correct?

You'll need one timer for each tone, and one timer to alternate the lights and control the tone.

A 555 timer can sink/source about 200 mA, but that might not be enough to drive the speakers. I'm have an idea, and I'll mock it up in Multisim before I post it.
 


JiggyNinja.
Pin 5 of a 555 allows some frequency modulation, so you can get two tones from one 555.
If you simulate it, could you check on the frequency shift you get with 100 K?
I suspect it may have to be smaller than 100 K.

Muhammad1993:
Two 555s would be better than one 556. The pin numbers on the 556 are different and you might find this confusing.

You seem to have this OK.

I limited the current in the speaker by putting a 47 ohm resistor in series with it.
This allows some direct current to flow in the speaker and you would need to put a capacitor in series with the speaker and remove the 47 ohm resistor if you wanted louder sound.

For a toy, this might be adequate, though. I have shown this capacitor in series with the speaker in the following diagram:
[PLAIN]http://dl.dropbox.com/u/4222062/2%20LED%202%20tone.PNG
 
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vk6kro said:
JiggyNinja.
Pin 5 of a 555 allows some frequency modulation, so you can get two tones from one 555.
If you simulate it, could you check on the frequency shift you get with 100 K?
I suspect it may have to be smaller than 100 K.
I know of the CONT pin, I just couldn't think of how to use it with this circuit. I've already got my breadboard out, so I'll do some experimentation at a slower frequency, see how it works.

The exact value of the resistor will likely depend on the two tones he wants for the siren.

EDIT: Breadboarded your idea. A value around 22K for the control pin resistor sounds perfect. Got a nice WEE WOO WEE WOO WEE WOO pitch to it, even if it is a little tinny (darn square waves). 100K is too big, and there wasn't enough difference in the pitches.

I didn't have a second 555, so I simulated it by flipping the end of the resistor from 5V to 0V with a relay.

Final advice to the OP, use a 9V battery to power this. It's within the 5-15V range the 555 needs for power, and connectors are really easy to find and solder in. Plus, the LED resistor values shown in vk's schematic are perfectly sized to let about 15 mA go through the LEDs at that voltage.
 
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What does uF stand for and jiggy ninja it would be helpful if you can tell me what you said but in noob terms i don't mean to take the mick I am just an amateur
 
  • #10


Muhammad1993 said:
What does uF stand for and jiggy ninja it would be helpful if you can tell me what you said but in noob terms i don't mean to take the mick I am just an amateur
It's okay, we all start out as newbs. :wink:

uF means microfarad, which is the unit for measuring capacitance. Specifically, 1 microfarad is 1 millionth of a farad.

By "breadboarded your idea", I mean that I actually built the circuit that vk6kro posted and tested it out. If you look at the resistor in blue connecting the two 555s together, he put a value of 100k there, but I found that 22k sounds better.

Since I only have one 555, I had to imitate the first one, which wasn't hard and isn't really important to know. It'll still work the same way.

555 Timers can be powered by anything from 5V to 15V. I think a 9V battery would be the best choice.
 
  • #11


EDIT: Breadboarded your idea. A value around 22K for the control pin resistor sounds perfect. Got a nice WEE WOO WEE WOO WEE WOO pitch to it, even if it is a little tinny (darn square waves). 100K is too big, and there wasn't enough difference in the pitches.

JiggyNinja,
Thanks for checking that. I have changed the resistor in the diagram to show 22 K.
 

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