Simulating an Expression Pedal with a Switch

[mobaar]

Hey folks,

Technically I'm new here as a contributing user, but I have done a lot of searching and research on this website, so I don't feel "new" here!

At any rate, I've recently purchased a DigiTech TimeBender pedal. First off, this pedal is amazing; I would wholeheartedly suggest it to anyone. I've compared it side-by-side with the Eventide Timefactor and it simply blows the TF out of the water in functionality. But that's also not why I'm here...

So I've figured out my strategy for a DIY version of the fs3x pedal to control the up/down memory bank and the looper function. However, I've been thinking about the expression pedal input. For those of you who don't know how it works, it is used to "morph" between 2 settings, so unison/octaving effects can be seamlessly switched over gradually. However, I see no real use for this feature, although I could see it being used in some capacity; it is just too rare for me to need, especially considering the real estate an expression pedal takes up.

I know full well that basic expression pedals are just variable pots, and the minimum level (aka zero resistance) and the maximum level (aka 100kohm, or 500kohm, or whatever, depending on the model) are the set levels for the 2 different "banks" of settings. So that got me to wondering whether I could use a switch that routes the connection between sleeve and tip of the mono cable either to a jumpered connection or a, say, 100k resistor, and, in essence, enable 2 separate banks of memory locations. One of the limitations of the TimeFactor is the fact that there are only 4 memory locations. If there are 2 saved settings for each of these memory locations, wouldn't a switchable banking of memory locations essentially give me 8 memory settings? So at that point, with 2 cables and a single enclosure, I could have 4 buttons - looper record, memory up, memory down, and memory bank selection...right?

I'm intrigued to try it out, but I don't want to move forward on it if someone questions my theory. Does switching from 0 to 100k resistance somehow get detected as not being a pot by the TB? Am I missing something?

I'd appreciate all your feedback. Ultimately, it's a theory that needs to be tested, but seriously folks, am I off on this?

Thanks!

~Mo

[Hides-His-Eyes]

It sounds like it should work, but it's the sort of thing I'd test out with croc clips (since it's so simple) in case there's something subtle going on with the pedal.

It might want to go betweeen o-100k-o--0--o and o--0--o-100k-o with a TRS jack rather than just TS.

[jkokura]

It should work, and another option is to use a variable resistor between the lugs rather than a regular resistor. The variable would allow you to change the resistance obviously, which could be valuable.

Jacob

[Processaurus]

Expression pedals, with a TRS cable coming out of them, use a pot as a variable voltage divider.  Supply voltage (probably 3.3v or 5v) comes from the pedal in the ring, which goes to the top of the pot, ground goes to the other end of the pot (sleeve), and the wiper goes to the tip, and that varying DC voltage from you wiggling your foot (between 0v and V+) back to the main pedal (tip)to be read by a processor or something.

Pedal V+ --------------------------RING-------------------/
                                                          \
Pedal reads this voltage----------TIP-------------------->/    (expression pedal pot, likely 10K or 100K)
                                                          \
Pedal Ground------------------------SLEEVE----------------/

So, you eliminate the pot, and want to substitute a SPDT switch in for the wiper, and switch the tip between the ring and the sleeve.  It would be safest to put a 10K resistor across the ring and sleeve to simulate the load of the expression pedal's pot, to the main pedal's viewpoint, in case it expects a load.

[Processaurus]

A thought: a momentary switch could be amazing.  I've made a bunch of them for friends' and my line 6 DL4s and it is a whole new game.  Also it precludes the need for an LED (though the LED in a latching switch could leech power off of the V+ (Ring) connection).

[mobaar]

well, to speak to the TRS suggestions you are providing, according to the manual, is needs a TS style cable and says the variable resistance should be between 100k and 500k log taper. taper aside, it is obvious this wont be put to rest until I DIY (err...DIM) so stay tuned. I may try some stuff out during lunch.

Thanks for the feedback!

~Mo

[Processaurus]

Oh, ok, that's easy, you use a SPST switch to connect the tip and sleeve together, with a 100K resistor permanently soldered across the two switch lugs.  Tip to Sleeve resistance is zero when the switch is closed, and 100K when it is open.