Hi
I am building a hobby project which involves using an induction coil as an eddy current sensor. I'm not an EE or an EE student; i'm just doing this for my own purposes.
I have a basic functioning circuit which pulses the coil at using a 555 circuit and some pots. The driving frequency range is currently adjustable between approx 32KHz and 87KHz which seems to work well with the various coil sensors that I have tested. The duty cycle is presently unknown as I don't have a scope.
The ability to tune the frequency to match the coil circuit seems to be critical as it's the variation in resonant frequency that I am using to measure the variation in inductance. It's presently working although in need of amplification.
I'm confident that I will be able to work my way through many of the challenges associated with the circuit itself but I have realised that choosing the oscillator mechanism is something that I should seek advice on.
What would be the best approach for creating a stable oscillating wave (of whatever shape) for driving a inductor at frequencies adjustable through my current range from 30KHz to 90KHz. Is the current 555 circuit my best choice or is there something out there?
I am expecting to have to wind my own coil sensor at some point and it may not have the same inductance as the commercial coils I am presently using. That's not a major problem except that it may raise the frequency required to be more than what the 555 is able to generate reliably.
What alternative would I use to create a stable adjustable frequency with a 50% duty cycle above 100KHz? I have had success generating a oscillating square wave of unknown duty cycle using a LM339 comparator which gave me up to approximately 150Khz. That was in a separate experiment and I have yet to revisit it.
Are crystals a better option? Or the ceramic resonators?
The current 555 oscillator adjustment is via pots but I would like to have it adjustable via micro controller so that I can do things like put in a temperature sensor and use that to adjust for temperature changes to further create stability (not asking how to do that because I think I can work that out myself).
Regards,
David
I am building a hobby project which involves using an induction coil as an eddy current sensor. I'm not an EE or an EE student; i'm just doing this for my own purposes.
I have a basic functioning circuit which pulses the coil at using a 555 circuit and some pots. The driving frequency range is currently adjustable between approx 32KHz and 87KHz which seems to work well with the various coil sensors that I have tested. The duty cycle is presently unknown as I don't have a scope.
The ability to tune the frequency to match the coil circuit seems to be critical as it's the variation in resonant frequency that I am using to measure the variation in inductance. It's presently working although in need of amplification.
I'm confident that I will be able to work my way through many of the challenges associated with the circuit itself but I have realised that choosing the oscillator mechanism is something that I should seek advice on.
What would be the best approach for creating a stable oscillating wave (of whatever shape) for driving a inductor at frequencies adjustable through my current range from 30KHz to 90KHz. Is the current 555 circuit my best choice or is there something out there?
I am expecting to have to wind my own coil sensor at some point and it may not have the same inductance as the commercial coils I am presently using. That's not a major problem except that it may raise the frequency required to be more than what the 555 is able to generate reliably.
What alternative would I use to create a stable adjustable frequency with a 50% duty cycle above 100KHz? I have had success generating a oscillating square wave of unknown duty cycle using a LM339 comparator which gave me up to approximately 150Khz. That was in a separate experiment and I have yet to revisit it.
Are crystals a better option? Or the ceramic resonators?
The current 555 oscillator adjustment is via pots but I would like to have it adjustable via micro controller so that I can do things like put in a temperature sensor and use that to adjust for temperature changes to further create stability (not asking how to do that because I think I can work that out myself).
Regards,
David