derrickr

I'd like to build a simple BPM counter for DJ use, that would plug in-line with the output from a mixer to the headphones, and display the bpm (to the the headphones) on a simple 3 digit led display.

I've been looking around the net and have seen others are also after a similar tool, but don't seem to be having any luck.

I believe the basic idea is quite simple : Low Pass Filter to produce a pulse that could be picked up by a counter/timer, which is then sampled over a failry short peroid and is then multiplied to give bpm, which is then sent to a simple LED driver circuit.

If anyone has ideas or circuit diagrams, I'd appreciate the feedback.

Many Thanks,

Derrick

Roff

Derrick, I'm not a dj or a musician, I'm an engineer. Your request sounded fairly simple to me at first, until I started thinking about music beats (you should have defined BPM - I had no idea what it meant until I started searching). I don't think the beat is necessarily always defined by bass notes. See this article.
I doubt that you can solve this problem with a simple circuit. That's why you find BPM counters on the internet that require human intervention.

derrickr

Sorry, I should've stated BPM = Beats Per Minute.

A standard DJ term use to define general 'tempo' of a song.

For the kind of application that I'm thinking of (club DJ use), I'm fairly confident that the bass tones will be sufficient to indicate the BPM/tempo.

I also think I'm actually getting there ! I've found a circuit that will do all the conversion and display on a three digit (seven segments each) LED, using a PIC16F84. I just need to experiment with the input filter to convert the audio to a pulse that the PIC can use.

Now if anyone's got good experience with that, or has a circuit diagram, that would be really cool.

Once again, thanks in advance.

Derrick

Roff

Take a look at this switched capacitor filter for your lowpass circuit. You can easily experiment with the cutoff frequency by changing the clock frequency. You can make a simple variable frequency clock oscillator with a 555 timer. I would follow the output of the filter with a Schmitt trigger (for hysteresis) made from an LM393 comparator. If you need schematics, I might be able to help as time allows.

derrickr

Thanks Ron. I've just ordered the parts to start experimenting, so hopefully I'll be able to get a prototype together in the next week (or two - work permitting).

Thanks again for the prompt feedback and other usesful links.

Cheers,

Derrick

p.s.
I'll let you know how it's going once I've got the prototype together. I'll probably need some more help ironing out the bugs

mxitman

Hey, I'm a former dj and had no luck finding something small like that, I just bucked up and bought a bpm counter that has 4 line inputs/ouputs works great, let me know if you build one that works. Might be a good investment.

Mxitman :wink:

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the sound

if your building a bpm counter then then think about the idea of useing a variable filter, 'cos typing as a dj you wont always want the bass counted(think D'n'B, the deeper sounds send a beat counter all over )
think of a 'tap counter':- you tap the button on each 'beat', and after three or four beats the counter gives you the numbers. It's a feature built into some mixers.
When you get all this together bare in mind many dj boothes in clubs/ parties/ wherevers wont have something as simple as a spare plug socket. BATTERIES ( and therfore a batt low indicator....)
hope this of some help, if not you can buy a beat counter( no tap ) for about 120 quid

Smirkenorf

I've been thinking about a similar project, and I'm a little stumped.
I can come up with a design which will allow me to get a pulsed square wave signal from an audio source. I can also design a circuit that will tell me the period between beats using a high frequency source (1MHz for example), counting the number of pulses between beats in binary form.
I can then convert to decimal output, placing the decimal point appropriately.

I don't yet know a way to get a decimal output of the frequency in beats per minute, which is what I'm going for.

If anyone can help, that would be great.

mister_e

25 years experienced in DJ myself.. those BPM counter are just useless and pointless to use. You should know your tunes and classified them accordingly anyways.

Even if pointless.. most intelligent gear have 'em built-in... but you don't want to trust them.

Agreed, that's a nice project to do...

DJM600, 3X SL1200MK2, 3X CDJ1000MKII.. that's my gear at night club and double it for home use

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geofftuke

I have a couple of beat counters I use on my computer by tapping on the space bar, (available free from www.kickit.to on their line dance page) but I want to get one either buy or make one I can carry with me in the car to count with and measure the tempo of any song I hear in the car.
This would need to be batt operated of course, but would not need to plug in to sense the bass impulses as I would be doing that. All it needs to do is count keystrokes and multiply by the time factor to display the actual number of beats per minute.
A deluxe option here would be a switch to divide the display from actual beats into bars per minute (simple division by 4 for 4/4 time or by 3 for 3/4 time [waltz])

Can anyone help me at all