solenoids and the noob

Discussion in 'The Projects Forum' started by Brokenman, Jul 5, 2008.

  1. Brokenman

    Thread Starter New Member

    Jun 8, 2008
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    Hello everyone, this is my first post here at All About Circuits and its basically a cry for help! I have been reading up on electronics now for a couple of weeks having started with a very specific idea in mind. My background is that of a creative music technologist, I design software and musical instrument interfaces. I have had the idea of creating a drum kit that is played with solenoids triggered by complex MIDI patterns and knew that I would have to be at least a little acquainted with electronics to accomplish this! Luckily most of the hard work has been done for me in the form of the fantastic MIDItron interface which allows you to output a voltage in response to MIDI data through 1 of 20 output terminals. They even give a fairly simple schematic for wiring up solenoids in conjunction with a transistor wired up to the MIDItron terminal which I have included below:
    [​IMG]
    Now I really am starting to put it all together in my head but just wanted to double check some stuff and ask a couple of questions before I go plugging my newly acquired rotary solenoid into the wall and cook myself! Please remember that I am incredibly new to electronics so please forgive my ignorance! Here goes:

    1) The solenoid that I have acquired has the following spec: 24Vdc drawing 0.79 amps. Now this my noobiest of noob questions, but do I have to worry about amps when deciding on a power supply? I know that if I change the supply voltage the amps drawn by the solenoid change so keeping the power rating at 18.5 watts so I suspect that the amps will just take care of themselves, so should I just be looking at the voltage of my power supply?

    2) The guys who gave me the solenoid said that I could increase the voltage to as much as 110Vdc and so achieve much, much more torque. However the duty cycle of the solenoid would be effected. Can anyone give me a little more info regarding duty cycle? Is it simply the amount of time that the solenoid can be switched on and that it has to be switched off in order to function correctly at any given voltage?

    3) I don't think that I will need to operate the solenoid at 110Vdc but I would like the facility to vary the voltage I supply to the solenoid from say 24Vdc to 70Vdc at my leisure (perhaps with a rotary pot of some kind) so allowing me to control the solenoids torque and so allowing me to control the force it strikes the drum. Any suggestions as to how I might do this?

    I plan to do allot more research before I go plugging anything in, so any ideas, suggestions or comments you might have would be so greatly appreciated! Many thanks.
     
  2. bertus

    Administrator

    Apr 5, 2008
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  3. Audioguru

    New Member

    Dec 20, 2007
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    The power supply must be able to supply 0.79A at 24V plus a little more current for the circuit.

    It is rated at 24V continuously. Its duty cycle can be reduced then it heats the same but has more torque for a short amount of time. Its 24V at 0.79A is 19W. Then it could use 48V at a 50% duty cycle 96V at a 25% duty cycle.
    You need to find out how quickly it heats.

    You need to control the voltage and the duty cycle at the same time.
     
  4. SgtWookie

    Expert

    Jul 17, 2007
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    Does the MidiTron support MIDI Velocity output?
    By that I mean, can you vary the duration of the output of a channel depending upon the velocity of the note?

    Usually, MIDI commands are sent as groups of one, two or three bytes; a status command (such as note on), then note number, then velocity. The MSB (most significant bit) of the status command is always 1, the MSB of a data byte is 0.

    Usually, you send a note on command with a note number and a velocity; then a note off command with the note number and aftertouch (release) velocity.

    If the MidiTron doesn't support velocity, you might instead use a form of PWM as in a monostable multivibrator or "one-shot". Use the output channel trigger the one-shot, which turns on a power transistor or MOSFET to give your solenoid a pulse of voltage for a controlled amount of time. Something like a 555 timer could be used, one per channel, in conjunction with a potentiometer to act as your "loud pedal".
     
  5. Brokenman

    Thread Starter New Member

    Jun 8, 2008
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    The terminal will output 0v when switched off or 5v when switched on. The output can be switched using one of the following MIDI input messages:

    Note On, Poly Pressure, Control Change, Program Change, Channel Pressure or Pitch Bend.

    The output switches on when the MIDI message’s data value becomes greater than or equal to the high threshold value which is set in the MIDItron editor and off when it becomes less than the predetermined low threshold value.
     
  6. Brokenman

    Thread Starter New Member

    Jun 8, 2008
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    So if the power supply can supply say 3A would that be okay? I'm guessing that it just can't be less.
     
  7. bertus

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  8. Brokenman

    Thread Starter New Member

    Jun 8, 2008
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    bumpity bump
     
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