metronome and 7 seg displays

thejamsh

New Member
im trying to use a picaxe as a metronome circuit, im new to picaxe and need a fair bit of help

firstly, i want to make a metronome that will beep from between 30 - 250 BPM (beats per minute)

this will be adjustable via two switches, when a switch is pressed once, the BPM will increase by 1, when the other switch is pressed, it will decrease by 1

i also want the tempo to be displayed between 3 seven segment displays

i have picaxe 28 chips at my disposal can anyone help me with the program basics and also the circuit itself? even provide a link to anotehr thread

i also want another switch to change the measure, between 4/4, 3/4 and 2/4.

the circuit will give an audible 'beep' for the beat and another slightly different beep for the measures in between

help very welcome
 

womai

Senior Member
Actually, I'd expect my code to be pretty accurate at those speeds. My example was for PWM at 120 Hz (i.e. 240 events per second); the metronome will only need less than 1/10th of that rate, so the overhead in the interrupt routine should be negligible. A second contributor could be the clock accuracy, but with an external resonator that tends to be better than 1%. I doubt those old mechanical metronomes could get even close.

Wolfgang
 

thejamsh

New Member
its not difficult to produce the metronome really its more adjusting the BPM AND then displayign that on a 7 seg display

the 7 seg displays are all driven by cascaded 4510 > 4511 arrangements. this can then count up or down over 3 displays

the handy thing is, it only needs one digital pulse to change the thing up or down, up or down can be changed by holding one input at high or low


any ideas how to get it to transfer over to this circuit to display the bpm?

thanks, and BTW the coursework is for A-level
 

bgrabowski

Senior Member
Interfacing a 7-segment display via a 4511 is covered in manual 3. Look up output device 10. It also covers the 4026 which uses fewer output pins so may be better for you. Do you require any further help with the BPM calculations?
 

thejamsh

New Member
calculating the bpm is not difficult, its getting the pauses correct

i have interfaced the picaxe quite easily with the 7 seg displays... its all a matter of keeping in sync

the difficulty i have is keeping a correct bpm with differnet measures
 

bgrabowski

Senior Member
Yes, you have to subtract the time it takes for the code to execute from your theoretical pause between beats. One way to find out this delay is to set your programme to say 60 bpm and then time say 300 beats with a stopwatch. The true time should be 5 minutes. If you get say 5 minutes 30 seconds each beat is 30/300=0.1 second too long. Using this process you can arrive at a constant value that you can subtract from the theoretical pause to keep the bpm reasonably accurate at any setting.
 
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