a little help please - Page 1
Forum section: electronics / beginners

author: xxngo
author_rank: Contributor
timestamp: April 20, 2015, 02:25:35 am
content: Can anyone tell me if I can vary the frequency range of a crytal oscillator with a tunning cap all the way down to 1Hz, I want to build oscillator circuits with a variable range from 1Hz to 1MHz and wasn't sure if I can fine tune a 12MHz crystal within that rage.thank you for all the help.

author: Richard Crowley
author_rank: Super Contributor
timestamp: April 20, 2015, 02:31:53 am
content: Absolutely not. At best you can "bend" the frequency of a crystal oscillator a fraction of a percent.It would appear that you need a frequency synthesizer. There are many chip-level and board-level solutions at very low prices.For example:http://www.ebay.com/sch/sis.html?_kw=UDB1005S+Function+Signal+Generator+Source+Frequency+Counter+DDS+Module

author: xxngo
author_rank: Contributor
timestamp: April 20, 2015, 02:40:53 am
content: Thank you very much, I thought I could get away with a tunning cap seen in the coltpitts oscillator circuit.. bummer guess I have to find a different solution.Thanks again

author: Richard Crowley
author_rank: Super Contributor
timestamp: April 20, 2015, 02:47:59 am
content: It is not at all clear why you think you need a crystal oscillator for something with a 1,000,000 to 1 ratio?It is not even clear that you can achieve such a humongous ratio all in one range with ANY simple oscillator.You seem to be seeking impossible solutions.Perhaps if you revealed the larger picture here, we might be able to suggest something appropriate.

author: xxngo
author_rank: Contributor
timestamp: April 20, 2015, 03:06:38 am
content: Im just a novice, my first year in electronic, and I wanted to create a function generator without having to use one of them IC like the XR-2206 which seem to be very promissing. I thought about using the 555 but unfortunately I believe that 100kHz is the max stable frequency that It can be vary it to I think, and so I looked up my text and saw the coltpitts with crystal and a tunning cap, and wasn't sure about the range that It can be vary.So yah, if you have other suggestions, please let me know. Thank you very much, I appreciate all the help

author: c4757p
author_rank: Super Contributor
timestamp: April 20, 2015, 03:21:19 am
content: If you looked at a 555, look at 7555. It's an improved version with over 10x the maximum frequency.

author: Richard Crowley
author_rank: Super Contributor
timestamp: April 20, 2015, 03:46:52 am
content: While the XR-2206 is rated for your range of 1 Hz ~ 1 MHz, it has only a 2000:1 tuning ratio. So you would need to switch through several ranges to get your desired range.And even the upgraded ICM7555 chip is only rated up to 500 KHz.

author: xxngo
author_rank: Contributor
timestamp: April 20, 2015, 11:33:04 pm
content: so in another word, I'm fuked hahahaha.....j/kyah I think I will go with the XR-2206 then, and hopefully I can find solutions for varying range of the chip.Although it would be nice if I can have expert's advice on how to go about it. That would be very helpful.Thanks again for all the help.

author: Richard Crowley
author_rank: Super Contributor
timestamp: April 20, 2015, 11:39:30 pm
content: Consider that any kind of control that had a range of 1,000,000 to 1 would be impossibly difficult to set to even a rough approximation of what you wanted. It would be overwhelmingly fiddly. You would be lucky to get it within 20 KHz of the desired frequency. What kind of user interface did you think you were going to use?That is why, here in the modern age, we use digital frequency synthesis where you can get your desired range, AND even sub-1Hz setting accuracy with very inexpensive technology.

author: xxngo
author_rank: Contributor
timestamp: April 21, 2015, 11:29:00 pm
content: I'm just trying to build a home use function generator for school project. I understand that in this digital age, everything is convience and within the price range. Its just my first year in electronic, I want to build something that can demonstate my understanding without having to use convience off the shelves solution. I'm not expecting it to be an awesome product at this stage, as long as it works...there are always room for improvement later on.Thank you for all your suggestion, and I really hope to learn alot more from everyone here.