Rock Band Double Kick Circuit

Discussion in 'The Projects Forum' started by Decepticon, Mar 30, 2009.

  1. Decepticon

    Thread Starter New Member

    Mar 30, 2009
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    First A little history:
    I am attempting to recreate a project that this guy made at Imakeprojects.com (http://imakeprojects.com/Projects/rock-band-dual-bass-drums-controller/ to be exact) I have recreated his circuit design with the exception of the
    74HC14 Schmitt-Trigger Hex Inverter which I replaced with an NTE74LS14 Schmitt-Trigger Hex Inverter. It has the same exact pinouts as the 74HC14 - I compared the data sheets for the two.

    I have tried and tried to make this thing work as expected but can get nothing out of the NTE74LS14. I have grounded all unused inputs as suggested on that site and I also have the 5v power supply built in as well. I can trigger the relay by hand using leads to +5 and Gnd - so I know that is not the issue.

    The circuit Diagram is attached as a jpg. Now, I am assuming from the diagram that all arrows pointing up are going to V+ and all arrows pointing down are going to gnd. Am I wrong in assuming this?

    As of now, I have it setup on a proto board so any suggestions can be implemented quickly and easily. I will also post pics of that when I get to my camera (at work ATM). Any help or suggestions would be greatly appreciated!


     
    Last edited: Mar 30, 2009
  2. Bernard

    AAC Fanatic!

    Aug 7, 2008
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    TTL input impedience is much lower than CMOS ,so timing will be different. I was disapointed with TTL schmitt triggers ,and would go for CMOS .
     
  3. Decepticon

    Thread Starter New Member

    Mar 30, 2009
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    Yeah, there was another design that uses the CD4001 logic chip (http://rockband.scorehero.com/forum/viewtopic.php?t=4801) but I had already purchased the parts for the original design I was gonna use. I looked at radio shack to see if they have the CD4001 and no luck there. I just wanted to avoid having to order a $.69 part and pay $5 for shipping it. Looks like I may have no choice now. Thanks for the input!
     
  4. peajay

    Well-Known Member

    Dec 10, 2005
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    Yes, I think you definately need the HC part rather than an LS part for that.

    I think your problem is that HC parts will output 5 volts for high and 0 volts for low, whereas LS parts will do about 2-3 volts for high and about 0.5 volts for low. The inputs differ as well, as LS components expect LS ouput voltages for input, and HC components expect HC output voltages for input.

    When the pedal isn't pressed, the output of the first inverter after the pedal is 5 volts, which discharges the capacitor after that to 0 volts since both pins are at the same voltage. When the pedal is pressed, the output of that inverter goes to 0 volts, which pulls the positive end of that capacitor to 0 volts for a short time until the resistor charges it.

    The problem you may be having is that since the LS components don't pull high very strongly, that capacitor is probably being discharged only to 2 volts or so, and when the inverter output goes low (to 0.5 volts), the positive end of the capacitor is then at 2.5 volts, which is still too high, and so the second inverter doesn't trigger.

    I'd be concerned about how long that circuit will last with the HC components. When you release the pedal, the output of that first inverter will return to +5 volts, and with a fully charged capacitor, that places +10 volts on the input to the second inverter, which is well above the absolute maximum rating. The inverter likely has internal diode clamps, so it will probably work for a while. (Personally, I'd expect it will probably work forever, even though it is technically incorrect.) Anyway, as long as you're spending $5 for shipping, you might want to order a few extra just in case it seems to work just fine for a while but then burns out at an bad moment, and I'd put it in a socket to make replacing one a ten second problem.
     
  5. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
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  6. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
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    While ordering you might as well get a dozen of the inverters, and perhaps a solid state relay to make the entire system more reliable/long lasting. If ordering from mouser, you will get free shipping if you hit the minimum order.
     
  7. Bernard

    AAC Fanatic!

    Aug 7, 2008
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    If you are concerned about input overload on 74C14, add about 10k in series with input or use 74C914 with added input protection.
     
  8. peajay

    Well-Known Member

    Dec 10, 2005
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    If you are concerned about input overload on 74C14, add about 10k in series with input

    Wow, that's perfect!

    I tried to think of a solution, but that never crossed my mind. ...and not just with this, but I was trying to find a nice solution to convert 5 volt CMOS signals to 3.3 volts, but every solution I came up with was either too slow (took too many microseconds to respond) or it involved a lot more parts than I wanted to use. ...but I just tried a 1K resistor between two inverters and it's barely any slower than without the resistor. It can't get any simpler than that.

    You just made my day. Thanks!
     
  9. Decepticon

    Thread Starter New Member

    Mar 30, 2009
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    Wow! You guys have been a great help. I am ordering a bunch of stuff from Mouser after this Friday and will use your suggestions. Thanks again for all the help!
     
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