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Author Topic: Simple (I think) problem with very basic drum machine trigger  (Read 870 times)
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Okey, I originally posted this on http://www.edaboard.com because it has nothing to do with Arduino, but as I couldn't solve it there and I think that Arduino forum has a lot more activity than the other one, and also there is a lot of people here that knows this stuff very well and helped me in the past. So I tried posting it here.

Thank you very much for taking the time to read this and help me!

I designed this circuit which I think is a pulse generator, made with a 555 IC, counter and an inverter to generate a ryhtm for the drum machine
Out of the picture (down) is a hi-hat circuit.

(those two things drew on the right by hand are buttons)
First of all this part is working fine, it generates a desired pulse and is having no problems by itself, also the hi-hat works fine in rhythm.

I also made two PCBs for this circuit:
which generate the snare and bass sounds and connected each one (bass and snare triggers) to the designed pins on the right of the first image. That also works fine by itself with the rhythm.

As I also want the drum and snare to be triggered by a button when the snare and bass rhyhtm is disabled (by disconnecting the switch on the right of the first image, next to the snare and bass rhythm output pins, labeled "X2_RITMO(OPC)") so I also connected a button to +9v and the other pin of the button to each trigger and THATS WHERE THE PROBLEM IS.

When I press the bass button it first triggers a bass drum sound, but when I realease it it makes a snare drum sound, also it seems that the snare button doesn't trigger the snare at all.


On the other forum a user kindly suggested I should put a diode in the bass wire, so that none of its switch action gets back to node 3.

So I made this modification:
but now it behaves in a weird fashion, when I press the bass button it makes the snare sound like a machine gun firing it very rapidly.

Any ideas what I could try? Thanks a lot!!!
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Could we talk you into replacing the whole circuit with an Arduino ?  smiley-evil
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It is not good connecting the output of a buffer directly to 9V when you press the snare trigger. This can blow up the buffer.

Forget the diodes and put another buffer between the base trigger and the input circuit.

If you need that manual trigger then turn that buffer into a logic gate. The type will depend on the normal state of the output of the 74LS93. If it is normally low then an OR gate should do. You should connect the input of the OR gate through a potential divider to get a safe input level to the gate. You should not feed over the supply voltage into a gate.
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Could we talk you into replacing the whole circuit with an Arduino ?  smiley-evil
hehehe... I'm trying to simplify things to make it small. I was planning to do it more complicated later after I finish this one.

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Forget the diodes and put another buffer between the base trigger and the input circuit.
I am very amateur at this... Do you mean to double negate the output of the bass trigger? I should point out that at this point it does work as intended when the rhythm switch is connected into one of the counter outputs, but maybe it can be damaged if left for a long time?

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If you need that manual trigger then turn that buffer into a logic gate. The type will depend on the normal state of the output of the 74LS93. If it is normally low then an OR gate should do. You should connect the input of the OR gate through a potential divider to get a safe input level to the gate. You should not feed over the supply voltage into a gate.
I really don't know what is the normal state of the 74LS93 counter is, the 555 timer is always running. I am sorry but got lost here, what OR gate? I know what it is, but there is none here... I think.

Thank you again for answering, it's not the first time you help me, Grumpy_Mike.
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I am sorry but got lost here, what OR gate?
The OR gate you need to put into your circuit at this point. You should not connect an output to a power supply no matter how you think it might be working for the moment. A 74LS02 is one such NOR gate you can use. That is an OR followed by a NOT function.
 
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I really don't know what is the normal state of the 74LS93 counter is, the 555 timer is always running.
So the state of the Qb output is two 555 time periods low and two high. Output Qd has 8 time periods low and 8 high. So all it does is to trigger the snare at different rates. That is why it sounds like a machine gun, it is just triggering the snare.
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