Arduino BPM- researching and building the display

breadboard with the start of the display
Breadboard with display and audio conector

I have started construction of the Display of my bpm counter, I decided to use the 7 segment displays instead of sending it to the serial connection, from what others have told me is that the serial connection lags a little and may screw up my timing of the audio signal.

I plan on hooking up 3 out of 4 digits using the same kind of method as building a POV display, by flashing the digits one at a time, fast enough, it will look like all 3 are on, but in truth only one digit will display for a very short time…. I have a drawn schematic right now, as soon as I finish the display I will post the schematic with a picture, and explain a little more on how i accomplished it.

The audio half has given me some trouble, I have not found a good example of how to measure the music and get a BPM. all the examples I have seen use human interaction, A few examples I have seen, use either a button or a piezo electric element, and all that it does is measure the time between taps, then averages out the last few to get the BPM, this does work but you still need human interaction, this is not ideal when listening to multiple tracks at the same time

My plan is to use a 741 OP-Amp to level the signal from the audio source and change it into a square wave that is measurable by my Arduino or other MC, Personally I would like to be able to select what audio range it is measuring but lets start simple and get a working measurement of some simple audio track and go from there.

The 741 op-amp is a versatile chip and can be used in so many applications from comparators to audio amplifiers. A great resource that I used to get a good idea how op-amps work (since I little experience in using them) is http:\talkingelectronics.com

the exact page I used is http://www.talkingelectronics.com/projects/OP-AMP/OP-AMP-1.html

the site has some great info, but the one on op-amps really goes into detail and has helped me design the (hopefully) ideal circuit for this application. A schmitt trigger looks like the ideal setup. I chose this as a starting point, the schmitt trigger only sends High signals, when a upper and lower threshhold are met other wise it is low on the outputs.

I will get more into my op-amp experiments once I start experimenting with them.

Look for my display update in the next few days!!!

P.S.  If any of you have any experience in op-amp circuits, your help will be appreciated greatly.