making voltage fluctuate rythmically

[Vitor Amaral]

Hello, is there any way to make voltage fluctuate up and down in a cycle of 5 seconds?

I am trying to make a small and simple circuit that makes a led dim in and out in a 5 second interval.


example: 0 seconds- 0V
1 seconds - 2V
2.5 seconds- 4.5v
4 seconds- 2V
5 seconds- 0V
etc....

Can you guys help me?

 

[cl10greg]

You can do it with software by ramping up and down a PWM. You can do it in hardware with switching transistors that are tied to the different levels you want. Software and PWM is the better solution

 

[betwixt]

You need a 0.2Hz oscillator with sufficient output current to drive the LED. You should be able to do it in 2 transistors, one as an oscillator and one as a current booster.

Brian.

 

[Gorgon]

Since the intensity of a LED is controlled by current and not voltage, the best way to dim it is to use PWM and a variable duty cycle. You set the max current by the output voltage and a resistor to generate the current through the LED, or you can use a special switch mode driver that generates a specified current. The driver is controlled by the PWM.
A small microcontroller would be best for the PWM and 5 second sequence control.

 

[Vitor Amaral]

Hey guys, i appreciate the answers, but i have a very low level technical knowledge when it comes to electronics. Can you please direct me to somewhere i can see more about this or use a very simple guide on how to do something like this?

 

[kam1787]

I think you want a triangle oscillator. You could do it using the 555 timer IC or Op-amps. Both the 555[with some help] and op-amps should be able to power a single ordinary LED. Remember to limit the current to the LED!

Do you have a power supply? A 555 needs a single-ended power supply (positive and ground) but it's triangle output is paltry - you would need to boost the current [common-collector mode transistor]. Op-amps usually need a dual power supply[positive, negative, and ground].

Keep in mind that the LED will not turn on until the triangle voltage exceeds the LED's forward voltage. Lets say you have a typical red LED with a forward voltage of 1.8V. When the triangle is starting, the LED will be off, until the voltage of the triangle exceeds 1.8V. Then it will be on until the triangle's voltage drops below 1.8V You can avoid that by biasing the LED until it is almost on.

http://forum.allaboutcircuits.com/showthread.php?t=40627
http://www.pcbheaven.com/userpages/Flexible_555_LED_Pulsing_Circuit/
http://www.electroschematics.com/5004/555-triangle-waveform-generator/
http://www.pcbheaven.com/circuitpages/Triangle_Wave_Generator/
http://forum.allaboutcircuits.com/showthread.php?t=90663
http://www.discovercircuits.com/H-Corner/Triangle-generator.htm
**broken link removed**
http://www.piclist.com/images/www/hobby_elec/e_ckt16_2.htm