# Help for Sine Wave generator

Discussion in 'The Projects Forum' started by LM317, Jan 3, 2013.

1. ### LM317 Thread Starter New Member

Jan 3, 2013
3
0
Hello guys! I am deisgning a sine wave generator that MUST provide accurate sine wave at desired frequency, in my case 5.5 Mhz.

this is the basic schematic, I decided to stop on Colpitis sine wave generator and ADD a crystal to stabilize the frequency further.
The voltage to power the board can be either 5 volts or 12 volts stabilized (or eventualy 12 volt battery that can range a little but that is not problem.)
What I need is:
To know where exactly is the output for the sine wave.
To be able to calculate all the resistors and eliminate all unnecessary resistors; Help with calculating the AMPLITUDE of the sine wave signal in Volts. I think its best to add some trimmer (potentiometer) because I need to be able to vary the amplitude of the sine wave from 0.5 to at least 5-6 volts or even more. Where should I add the pot?

Finally, where should I add the crystal? Should it be the same frequency as the one I want to have?
As far as the 2 capacitors connected to the inductor, I have already calculated them using this calculator to match 5.5 Mhz, so I dont think I will need help with that for now.
Heres is the schematic and link for Colpitis sine wave calculator I used.
http://www.ekswai.com/en_cap3.htm
http://i45.tinypic.com/6sykud.jpg
Thank you very much in advance!

2. ### crutschow Expert

Mar 14, 2008
20,262
5,737
This should give you some help.

3. ### bountyhunter Well-Known Member

Sep 7, 2009
2,498
510
accurate frequency or accurate meaning very low distortion sine wave?

don'ty know what you are saying there. Frequency, amplitude, distortion?

4. ### Ron H AAC Fanatic!

Apr 14, 2005
7,049
674
Don't build and test this one. Your inductor is across the power supply, and will disappear in a puff of smoke.

5. ### LM317 Thread Starter New Member

Jan 3, 2013
3
0
I just want to have accurate sine wave when it comes to its shape. I also want to be able to change the amplitude from 0 (or at least 0.5) Volts to up to 5 or 6 volts.
About the output: On the circuit I have given, whee do I get the sine wave? I mean from which wire is it going to show the sine wave if I connect oscilloscope?
About the inductor across the power: thats the way the circuit is, in the link I gave where I get the information from.
OK lets say I decide to make this type of oscillator
http://freecircuitdiagram.com/2009/07/10/colpitts-crystal-oscillator/
how should I calculate the values for the capacitors and inductors and the frequency of crystal to get 5.5 Mhz sine wave on the output of this type of circuit?

6. ### Brownout Well-Known Member

Jan 10, 2012
2,373
1,003
If you seriously don't know how to get started, you're much better off just buying a crystal oscillator and using it. They are cheap and pleantiful, and will operate much better than one you can build. If you can't get one in your exact frequency, then chances are there aren't crystals made for that frequency, so you wouldn't be able to build one anyway.

7. ### bountyhunter Well-Known Member

Sep 7, 2009
2,498
510
If you need a "non standard" frequency, you have to get a higher crystal frequency and divide it down using digital down counters.

8. ### DickCappels Moderator

Aug 21, 2008
5,008
1,521
Digikey has 5.5 Mhz crystals in stock.

As far as component values, there are no inductors in that circuit, so you don't have to worry about inductors. I would start with the capacitor and resistor values shown in the schematic to which you linked. That circuit is not very fussy when it comes to component values.

To make the output variable, put a 1k pot in parallel with the emitter resistor.

The tricky part will be getting the output up to the five or six volts you asked for. I suggest that accomplish that with a separate amplifier once you get the oscillator running.

9. ### LM317 Thread Starter New Member

Jan 3, 2013
3
0
Ok since its difficult to find 5.5 mhz oscillator, I will go for the circuit that has none. (only 1 inductor and 2 capacitors to get desired frequency. Does anyone know if it will be needed to put the other capacitor on the base for example? I think it is working as some sort of filtering capacitor....

10. ### Brownout Well-Known Member

Jan 10, 2012
2,373
1,003
If a component is on the schematic, then chances are overwhelming that it will be necessary.

11. ### Ron H AAC Fanatic!

Apr 14, 2005
7,049
674
Is the output of your oscillator going to drive a load? If so, what is it?