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Thread: best way to change voltage?

  1. #1
    daz
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    ..
    Last edited by daz; 05-05-2017 at 07:29 PM.

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    Old Timer J M Fahey's Avatar
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    Run out of spinach, Popeye?
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  3. #3
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    Damn touch screens and their text-box auto-abort feature!

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  4. #4
    Senior Member Enzo's Avatar
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    Maybe it is the umlaut mod.
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  5. #5
    Supporting Member The Dude's Avatar
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    I find the 3 dot method a much better way to change voltage.
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    “Yeah, well, you know, that’s just, like, your opinion, man.”

  6. #6
    Senior Member Enzo's Avatar
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    Dot's a good point. But I am not sold on this approach, PERIOD.
    Education is what you're left with after you have forgotten what you have learned.

  7. #7
    g1
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    Quote Originally Posted by daz View Post
    ..
    You're one dot short of an ellipsis.
    Last edited by g1; 05-06-2017 at 01:15 AM.
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    Certified Dotard

  8. #8
    Senior Member Enzo's Avatar
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    Solar ellipsis or lunar ellipsis?
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  9. #9
    g1
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    Actually, Tales of Brave Ellipsis.
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  10. #10
    Senior Member Enzo's Avatar
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    Oh yes, the famous Greek warrior. CLose friend of Damocles, Hercules, and Testicles.
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  11. #11
    Supporting Member Chuck H's Avatar
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    Dot mess with daz. Sometimes you just dot see the error in your logic before you post. You have to erase it or just leave the post up and look foolish like you dot have skills.

    Dammit! I forgot my n's again.
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  12. #12
    daz
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    Ahhhh, ya bastids !!! Sure, have fun at my expense just cuz i'm a sub moron. Sub morons have feelings too ya know ! Ok, on a serious note, i have a question where the original one was till i answered it myself. So in this digital expression pedal theres a light or movement sensor or whatever that the pedal swipes a white plastic thingamajig by to change the volume level. I can read resistance changes in one position to the other in 2 places. Do you think i could remove the sensor and put a pair of resistors in it's place to mimick a given pedal position that i've read and noted? Basically what i want to do is use a DPDT switch to switch between the resistors so i can switch between two levels of my choosing based on the resistance i read at the pedal positions i need to switch between. Does this sound doable? I just basically want a switch to choose between 2 levels rather than have to rock a pedal back and fourth trying to find the right lower level.
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  13. #13
    rjb
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    Quote Originally Posted by daz View Post
    ...I just basically want a switch to choose between 2 levels rather than have to rock a pedal back and fourth trying to find the right lower level.
    Are you using the pedal for anything other than a 2-position volume control?
    If not, just jam a shim under the lever so it stops at the desired lower level!

    -rb, idjit-at-large
    Last edited by rjb; 05-06-2017 at 11:39 PM. Reason: Shortened quote

  14. #14
    daz
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    I already thought of that and also just configuring he heel/toe settings in a certain way but the thing is i hate having to build a new pedal board for it and it's heavy and cumbersome. Plus i could use a 4PDT switch and have it set up with a LED. So fir a number of reasons i can't/don't want to use the pedal.

    I had the guts out of it with my last amp and just mounted in the board and it was great. But that amp allowed me to configure it in it's firmware so i could make it work without having to mod it. this new mp doesn't have the same config so i can't use it the same way.

  15. #15
    Old Timer J M Fahey's Avatar
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    You can build a new pedal ............ hey!!!! ..... stop hitting me with a lead pipe ........ it hurts !!!!!!!!
    Just a passive one in *any* case, even a sardine can (emptied of sardines of course)

    Input/output jacks, SPDT switch (or better), 2 fixed resistors or, way better, a 1M volume pot, switch selects between full and attenuated signal, whatever value you wish.
    Juan Manuel Fahey

  16. #16
    daz
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    It's a digital controller, not a signal if thats what u r suggesting. theres no guitar signal involved. I have no problem with the building end. I just want to know if anyone is familiar with the way these things operate with the sensor and whether i can remove the sensor and put in place resistance that i measure at the sensor at 2 different points in the pedal position and switch between them. i mean, is that all the sensor is, is a light sensing variable resistor?

  17. #17
    Senior Member Enzo's Avatar
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    It is an LED, usually infrared, but sometimes visible, shining on a phototransistor. We'd have to see the circuit, as it alters the current conduction of the transistor.

    So what is the damned thing, someone might even have the schematic?
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  18. #18
    daz
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    it's a fender EXP-1 expression pedal. It's not an opto because those use a light sensitive resistor and LED and this is what looks sorta like a chip with a glossy black surface thats apparently sensitive to movement. The pedal has a white strip of plastic about an inch long that swipe past it with pedal movement. Here's the sensor....
    sensor.jpg
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  19. #19
    Senior Member Enzo's Avatar
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    Photo transistor, not photo cell.

    See there are two devices side by side? One is an LED emitting light, the other is a photo transistor of some sort, I'll bet my lunch money. Light reflecting from one into the other is what the plastic strip controls.

    There are two resistors and two semiconductor devices that I can see, but I also see plated through screw holes. making me think the other side of the board has tracery. Is there? In any case, you can draw out the schematic of this little board in a few minutes.

    Digital cameras can often see infrared that our eyes cannot, so aim your phone cam or other digital camera you might have at this board while it is powered, and see if the smaller thingie looks lit up.

    Or just measure for voltage drop across the smaller part, I bet the 560 ohm resistor is a current limit for it. Do you see an LED-like drop? Holding a white paper (business card?) right over them should reflect light into them, mesure for either resistance or voltage drop across the other device, whichever pins seem to connect somewhere. Now cover it with something opaque, does the reading change?
    Education is what you're left with after you have forgotten what you have learned.

  20. #20
    Old Timer J M Fahey's Avatar
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    Quote Originally Posted by daz View Post
    it's a fender EXP-1 expression pedal. It's not an opto because those use a light sensitive resistor and LED
    You should add: "the ones *I* know"
    and this is what looks sorta like a chip with a glossy black surface
    Plastic which is transparent to infrared may look like *dark* red or plain black to our eyes.
    thats apparently sensitive to movement.
    think how would it achieve that.
    The pedal has a white strip of plastic about an inch long that swipe past it with pedal movement.
    I think it´s a reflective distance/position sensor, which sends an infrared beam upwards, reads reflected light with an integrated phototransistor , that´s why it needs the reflective white plastic.
    As opto as I ever saw.
    You should ask Fender the schematic, and as a backup read any code printed on the IC, search its datasheet and suggested applications.
    And tell us
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  21. #21
    Supporting Member Jazz P Bass's Avatar
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    And please touch up the solder joints on the two left most wires.
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  22. #22
    Senior Member SoulFetish's Avatar
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    I think this is the best start to a thread I've ever seen in my life. LMAO.
    I haven't even made it to the part that it's actually about yet.
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    If I have a 50% chance of guessing the right answer, I guess wrong 80% of the time.

  23. #23
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    My friend Steve who used to repair old transistor and tube TV sets, back in the day, said: get 2 x 1000 foot extension cords. That'll drop the voltage. When you want to turn it on, just ask your neighbor to connect the two extension cords.
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  24. #24
    Supporting Member Chuck H's Avatar
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    I just put a hose clamp on a standard extension cord and adjust the pressure.
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    "I've heard magic defined as "a technology you don't understand". By that aphorism, the folks in this forum are practicing wizards, able to summon AND control the lightning demon, and make charms to allow others to use the demon in certain ways." R.G.

    "...less ear-friendly but handy for jazz." Leo_Gnardo

  25. #25
    daz
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    Then mounting holes are not part of the circuit on either side of the board. The small part DOES light up using my camera. As for voltage drops or resistance changes, i can't measure it. I can swipe my finger or anything past the sensor and it does change because i can hear the amp volume change. Anything i swipe by it changes that. But I tried but holding the probes on such tiny points and trying to swipe my finger by it while holding the probes but i just can't maintain contact while doing that so the readings are all just intermittent/wonky. I guess i'm gonna have to pass on this. Thanks for the help tho. Maybe they will add a firmware update that will make it do what i want because it does appear the firmware is not working exactly as it should. But for typical purposes i don't think they will care because no one pulls the circuit board and uses it out of the pedal, and when in the pedal the bug in the firmware doesn't matter. Long story that will probably bore you so i'll leave it at that. anyways, thanks for the info.

    Quote Originally Posted by Enzo View Post
    Photo transistor, not photo cell.

    See there are two devices side by side? One is an LED emitting light, the other is a photo transistor of some sort, I'll bet my lunch money. Light reflecting from one into the other is what the plastic strip controls.

    There are two resistors and two semiconductor devices that I can see, but I also see plated through screw holes. making me think the other side of the board has tracery. Is there? In any case, you can draw out the schematic of this little board in a few minutes.

    Digital cameras can often see infrared that our eyes cannot, so aim your phone cam or other digital camera you might have at this board while it is powered, and see if the smaller thingie looks lit up.

    Or just measure for voltage drop across the smaller part, I bet the 560 ohm resistor is a current limit for it. Do you see an LED-like drop? Holding a white paper (business card?) right over them should reflect light into them, mesure for either resistance or voltage drop across the other device, whichever pins seem to connect somewhere. Now cover it with something opaque, does the reading change?

  26. #26
    daz
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    The mounting holes are not part of the circuit on either side of the board. The small part DOES light up using my camera. As for voltage drops or resistance changes, i can't measure it. I can swipe my finger or anything past the sensor and it does change because i can hear the amp volume change. Anything i swipe by it changes that. But I tried but holding the probes on such tiny points and trying to swipe my finger by it while holding the probes but i just can't maintain contact while doing that so the readings are all just intermittent/wonky. I guess i'm gonna have to pass on this. Thanks for the help tho. Maybe they will add a firmware update that will make it do what i want because it does appear the firmware is not working exactly as it should. But for typical purposes i don't think they will care because no one pulls the circuit board and uses it out of the pedal, and when in the pedal the bug in the firmware doesn't matter. Long story that will probably bore you so i'll leave it at that. anyways, thanks for the info.

    Quote Originally Posted by Enzo View Post
    Photo transistor, not photo cell.

    See there are two devices side by side? One is an LED emitting light, the other is a photo transistor of some sort, I'll bet my lunch money. Light reflecting from one into the other is what the plastic strip controls.

    There are two resistors and two semiconductor devices that I can see, but I also see plated through screw holes. making me think the other side of the board has tracery. Is there? In any case, you can draw out the schematic of this little board in a few minutes.

    Digital cameras can often see infrared that our eyes cannot, so aim your phone cam or other digital camera you might have at this board while it is powered, and see if the smaller thingie looks lit up.

    Or just measure for voltage drop across the smaller part, I bet the 560 ohm resistor is a current limit for it. Do you see an LED-like drop? Holding a white paper (business card?) right over them should reflect light into them, mesure for either resistance or voltage drop across the other device, whichever pins seem to connect somewhere. Now cover it with something opaque, does the reading change?
    mikepukmel likes this.

  27. #27
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    Whenever I get a 'not enough hands' situation I temporarily tack a couple of fine leads onto the solder joints and attach my meter to those via a couple of short clip leads.

    Those phototransistors are usually connected internally to a collector-emitter junction. I think of them as the light controlling the base in my internalized 'flat-earth' model.
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  28. #28
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    Quote Originally Posted by Chuck H View Post
    I just put a hose clamp on a standard extension cord and adjust the pressure.
    Chuck, what kind of torque wrench do you use on the hose clamp? Do you set the torque wrench to milli-micro-nano inch pound millimeters?

  29. #29
    Old Timer J M Fahey's Avatar
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    Quote Originally Posted by mikepukmel View Post
    Chuck, what kind of torque wrench do you use on the hose clamp? Do you set the torque wrench to milli-micro-nano inch pound millimeters?
    Torque wrenches are for sissies.

    We Macho men use our bare arms:
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  30. #30
    Supporting Member Chuck H's Avatar
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    Those things are creepin' me out.
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    "...less ear-friendly but handy for jazz." Leo_Gnardo

  31. #31
    Old Timer Leo_Gnardo's Avatar
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    Quote Originally Posted by Chuck H View Post
    Those things are creepin' me out.
    They kinda look like industrial strength relatives of the shmoo.


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