Actions
Forum Thread Details
  • State Verified Answer
  • Replies 18 replies
  • Answers 1 answer
  • Subscribers 95 subscribers
  • Views 4401 views
  • Users 0 members are here
Related

Colpitts Crystal Oscillator Circuit

jw0752

In the last couple days I have been experimenting and learning about crystal oscillator circuits. I am doing this with no particular application in mind. I have been able to get a couple circuits to work as expected but there is one circuit that I got from the book " Practical Electronics for Inventors" by Paul Scherz and Simon Monk that I have not been able to get working. I have tried different transistors and I have tried varying the values of the support passives. I am wondering if anyone has had experience with this circuit and can give me a hint as to where to look for my failure to get it to work. There is also one other possibility. This book has been known to include errata from time to time so I wouldn't be completely surprised if there is something wrong with the circuit. Any insights would be appreciated.

 

John

 

 

image

Parents
  • 0

    Hi John!

     

    Many of these circuits can be very critical and dependant on the actual components and trimming that the original author used : ( because usually the older (and sadly many newer) oscillator designs on the web are designed by trial-and-error (or copied), not by any other method. It may be oscillating, but the output may be low (a hundred mV or lower maybe). How are you testing it? One quick way to check is to try to tune a radio to that frequency (some short-wave receivers will have that on the end of one of their bands). If you don't have a radio that goes to that frequency, you could try to tune to a harmonic (unless you got super-lucky : ) the design will have harmonics to some extent, although the output is not a square wave.

Reply
  • 0

    Hi John!

     

    Many of these circuits can be very critical and dependant on the actual components and trimming that the original author used : ( because usually the older (and sadly many newer) oscillator designs on the web are designed by trial-and-error (or copied), not by any other method. It may be oscillating, but the output may be low (a hundred mV or lower maybe). How are you testing it? One quick way to check is to try to tune a radio to that frequency (some short-wave receivers will have that on the end of one of their bands). If you don't have a radio that goes to that frequency, you could try to tune to a harmonic (unless you got super-lucky : ) the design will have harmonics to some extent, although the output is not a square wave.

Children
  • 0 in reply to shabaz

    Hi Shabaz,  I am looking at the output with a scope and I can go down to 20mV per division. I am seeing a lot of noise but nothing else and the scope can't read a frequency. The shortwave radio is a good idea and I may just get mine off the shelf when I get this going. It should give me a way to detect the harmonics to some extent too. Thanks for the ideas.

    John