0
\$\begingroup\$

Is a simpler question just how do you control capacitance or inductance with a microcontroller?

If that isn't possible then I've read something about using PLL's, but I do not understand how it tunes to a specific frequency, only how they synthesize a new frequency.

I commonly see digital tuners on all sorts of devices so it seems like there should be a straightforward way.

\$\endgroup\$
  • \$\begingroup\$ Is it not possible to use a RC receiver designed for microcontroller control? \$\endgroup\$ – gbulmer Sep 20 '15 at 4:07
  • \$\begingroup\$ There mere fact that a technique is used in common gadgets does not mean that it is straightforward! Microprocessors, GSM transceivers, GPS receivers, even a modern combustion engine are all far from straightforward. For PLLs: google, the principle is not that difficult, and there are plenty of explanations out there. \$\endgroup\$ – Wouter van Ooijen Sep 20 '15 at 8:26
2
\$\begingroup\$

In simple terms by mixing (multiplying) a signal with a specific frequency (lets call it F) with a second frequency (lets call it G) you get two output frequencies F+G and F-G. If assuming that F is a high frequency then subtracting G gives you a lower frequency. Then by passing the signal through a band pass filter to eliminate unwanted frequencies you get a signal that something can be done with, demodulated and played over speakers, sampled and analyzed for digital content,... By using a micro to control the G frequency the micro can change the frequency from F that falls inside that band pass filter.

Further if using a Superheteradine tuner the micro can control two different frequencies to give even greater frequency range.

|improve this answer|||||
\$\endgroup\$
1
\$\begingroup\$

Digital circuits can tune their cut-off frequency by means of digital passive elements. In these devices they use "Varactor Diode" for a digital variable capacitor. If you reverse bias this diode, you can control it's capacitance. For variable resistance these circuits, use digital POTs like mcp41xxx. Indeed these circuits use "Tunnel Diode" for making a "Negative Resistance" that is controlled by voltage.

These voltage controlled passive elements, can be used in a PLL to lock to a desired frequency, and all things is in the hands of a controller unit like microcontrollers.

|improve this answer|||||
\$\endgroup\$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.