Instructables

Waveform Generator

Hi guys!

So actually i wanted to make a circuit that can turn on and off an LED array at a particular rate (say 10 seconds time period). I want the LEDs to gradually brighten and dim. At first i thought i can implement it using a multi vibrator, but it it turning off and on too fast, since the output of the MV is a square wave. I want to design a simple circuit that can generate more slowly rising waveform (like sine or triangular) and can also drive a load of at least 100 mA and have a time period of 10 seconds or so. Any suggestions? 

Orngrimm1 year ago
How long should it phase in and out?
If only a second or so, you can add a resistor and Capacitor to dampen the transients.
charmquark (author)  Orngrimm1 year ago
well i can do it, but the resistor will limit the current drawn too much. say, i want a time of 10 seconds, that makes 1Mega ohm * 10 micro farad. The resistor will drastically reduce the current that reaches the load. This very limitation makes me look for alternatives
10sec of fading with 10sec period? So always-fade... OK... In this case the RC-configuration wont work.
Would a simple sawtooth / triangular-waveform (with offset) fit your needs or does it have to be a sine with offset?
charmquark (author)  Orngrimm1 year ago
I am making certain assumptions here. If the waveform is slowly rising, with a time period of say 10 seconds, then i can make my LED array such that when it reaches the peak of its waveform, it glows with maximum intensity and when it falls below, the LEDs will dim out. So any slowly rising waveform like sine or saw-tooth/triangular will do. The square waveform reaches its peak too fast, so i want to avoid it.

Also, can i use a BJT instead of the FET? The FET may not be available where i live, so do suggest me some alternatives
Also the quite common 2N7002 works...
http://www.bilderload.com/bild/276753/10secFA2T1.png

What exactly is a BJT?
You can use whatever FET you have around... Simply check for the specs if it is capable of supplying the current, being able to be switched by the voltages you have here and if it is the correct type (N-channel enrichment-type).
I simply took the FDS6614A in the simulation because i just had no other type at hand...

So why not simply use a FET to change the impedance and enable the drive of huge loads?

See the quickly simulated circuit @ http://www.bilderload.com/bild/276215/2ampsawtoothV272R.png i made for you.
See the 2 different voltages and the resulting current in the top-part of the image.

It is split into 3 parts:
Frequenzy-generation
Waveform-changing
Impedance-changing

You can drive many amps with that if you want...
Orngrimm1 year ago
Oh: The formula to charge a capacitor to its voltage is
t=5*R*C

Pro

Get More Out of Instructables

Already have an Account?

close

PDF Downloads
As a Pro member, you will gain access to download any Instructable in the PDF format. You also have the ability to customize your PDF download.

Upgrade to Pro today!