I’m president of a high school electronics club, and having completed all the intersting kit projects plus some others we made up, I decided to try to build a musical instrument tuner. I’ve just got one problem. I don’t really know how they work. I tried writing to companies that manafacture them, asking for an explanation or schematics for their simpler LED models, but they either didn’t respond or wrote back that they weren’t allowed to give out proprietary schematics.
Is there anyone out there in the teeming millions who does know how these things work?
I don’t have a schematic for you, but musical instrument tuners are common projects in electronics magazines like “Popular Electronics”. Check their websites or back issues.
I remember making one when I was in tech school, many moons ago. For the transducer I used a resonant reed filter tuned for 55Hz, which is the frequency of the A string on a bass guitar if my 38 year old memory serves. It was connected by way of an amplifier circuit to a center-scale meter like this. The filter was sensitive enough that the meter’s deflection was only a few hertz either way. Once the A string is tuned, the other strings can be tuned using that as a reference.
The transducer/sensor will be the hard part. I suggest building it for a single frequency, otherwise you’re faced with the problem of building a tuner with a flat response.
I doubt I saved my plans, but if anything turns up I’ll post more.
Um…Attrayant, that reed filter goes for $75 and, well, one of the reasons I was wanting to build the tuner was to save money. Does anyone have any more frugal suggestions?
I actually was idly wondering about tuners myself recently and did some looking into it, so here’s a few thoughts.
A stroboscopic tuner is simple to understand but might be difficult mechanically (you have to have a precision marked disk and rotate it properly to get good results). If you have a properly graded disk, you generate the strobe light proportional to the measured signal and watch the apparent rotation of the disk.
I think the vast majority of compact tuners made today are frequency/period counters. Usually you count the number of pulses in the signal. Then you figure out the longest period in the signal, which will be that the note sounded (you have to measure a bunch of zero crossings due to harmonics, but since it’s a musical note you can still get the fundamental) . With clocks in the MHz range it’s easy to get high precision. It also has the advantage of being auto-chromatic.
Of course, you do it all digitally this way, so you probably need a microprocessor or maybe a good FPGA to do it. If you just aim for one frequency & bandpass it (or use a tunable filter) you might simplify this a great deal – then all you’d need is a counter and a way to convert the periods to frequency (actually, I suppose an analog ramp could work to measure time too, but you need a way to start & stop it).
An older, but somewhat interesting method I found (and it was patented in 1973 or so, so you can get a full description on it) is to use a PLL. You set your VCO to be free-running at the correct frequency. Then when it locks (to the input signal) you use the difference output (which is driving the VCO) to tell if you’re high or low. The precision’s likely only to be good for a few Hz and it’s fixed to a single frequency but I think it’d be nice project and easy to make.
I’ve seen electronic guitar tuners priced at 15 bucks. These are designed to register the six notes used in standard guitar tuning. Chromatic tuners are available for not very much more.
Assuming your main goal here is to BUILD a tuner, perhaps buying one and disecting it would tell you what you need to know.
If you only wanted to POSSESS a tuner, I would think simply buying one would be the most cost- and time-efficient approach.
Here’s a link to something I’ve been planning on trying, but of course, have never found the time to get into it. It’s not a tuner, but it gives visual feedback of what pitch is being played. It’s meant for instruments allowing continuous pitch change, like fretless bass, violin, or a theremin which is what it was designed for. The visual feedback is in the form of LED’s layed out like a standard keyboard. It’s not exactly what you are looking for, but maybe it will lead you in the right direction. There are links on the page for the schematics, part list, etc.
To fulfill the cost reason, anyway, if not to fulfill the OP…
Here’s a FREE “tuner”…just know that A=440 (in most cases), B=493.88, and so on…http://www.esser.u-net.com/ttg.htm
A link for the frequency list as well…http://http://www.phy.mtu.edu/~suits/notefreqs.html
