Building a Banjo Tuner Prototype for a Logic Circuits and Switching Theory Class

Thread Starter


Joined Feb 7, 2012
Forgive me for not being knowledgeable enough on this subject yet as I've just taken it up recently but for our prototype project, I've chosen to do a four-string banjo tuner. What I plan to do is similar to that of a guitar tuner with LED's lighting up to indicate whether the string is flat, sharp, or in tune and I know that this will be pretty simple to make once I learn to fully understand the concept.

But please note that I'm still learning the different types of logic circuits so I was wondering if any of you could give me a guide on how I will start building the circuit in a breadboard. I'm still not familiar on the types of components I need for the circuit to detect the frequency of the string until it matches to the correct one and how a logic gate will come into play when indicating which LED should light up. We need to apply either sequential logic, counters, or registers but we haven't studied all of them yet so any kind of information about this will really be helpful.


Joined Oct 2, 2009
The purpose of all design classes is not just about learning electronics but how to develop and apply analytical skills. No one here on AAC is going to give you a solution on a platter.

Think about it. Start off with tuning one string. How would you detect the pitch of the note?


Joined Mar 14, 2008
Another way is a phase detector that detects the difference between a reference frequency and the banjo string frequency. You could use the Type II logic phase comparator in the CD4046 PLL. That type of comparator will give one logic state output when the banjo frequency is greater than the reference and the opposite logic state output when the banjo frequency is less than the reference. As you near the reference frequency it will switch between states. So you adjust the banjo frequency until the indicator are more or less equally on.

There's no calibration involved in this circuit as long as you have an accurate crystal clock source to generate the reference frequencies.