Capacitor value designing Q

[idlefaction]

okay, can anyone think of a way to hook up capacitors with an SPST switch, so that when you close a switch the capacitance value drops?

if you connect them in series and short one out, the capacitance rises; if you connect them in parallel and switch one in, the capacitance still rises.  aargh!!!

i'm trying to hook up a on-off-on DPDT switch as a three-mode selector for a twin-t/Q&D style wah, using these end values:

1.  0.01uF, 0.0068uF
2.  0.0022uF, 0.0068uF
3.  0.0022uF, 0.001uF

i can't figure out any way to have the switch change the 0.0068uF to a 0.001uF in one position only, remembering the middle position still has to be 0.0068uF.  :/   help!!!

[stylus]

simple, have the original value made out of the two ones combined when one is shorted, then when they are on the lower capacitance

[idlefaction]

i wish!!!!

to add capacitances, you add them in parallel.  so if you short one... you short them both!  

[Ansil]

more poles on the switch

[idlefaction]

yeh i'm pretty much giving up the dream.  i'll use a rotary instead.  thanks  

[Bill_F]

Maybe I'm misunderstanding. But couldn't you use a switch like this?

[idlefaction]

the important bit is that the capacitance has to drop when the switch *closes*.  when you close that switch, the capacitance gets more.  

and if you do it like:

Code Select Expand

 ,-/ -.
-*-||-*-||--

when you *close* the switch to short out a cap, the total capacitance also rises.

another option is to have middle the lowest setting, and either side a variation of higher settings.  but i'll go with a rotary - it's a good excuse to use a chicken head knob  [/code]

[gez]

Wire up two caps in parallel and 'open' the switch so that one gets disconnected, it's just a matter of perception!  

[idlefaction]

cool, all i need is a DPDT on-off-on switch, where one pole has the middle NC and the other has the middle NO  

hence the problem!!  but thanks for everyone's ideas.  chicken head rotary switch it is.  

[gez]

i'm trying to hook up a on-off-on DPDT switch as a three-mode selector for a twin-t/Q&D style wah, using these end values:

1.  0.01uF, 0.0068uF
2.  0.0022uF, 0.0068uF
3.  0.0022uF, 0.001uF

OK, I should have read your post more thoroughly.  Here's one way you could do it, but it's a compromise:

.0068 -     - .0068
.0022 -     - .001
*****-     - .0068

This would give you:
.009, .0078 (1)
.0022, .001 (3)
.0022, .0078 (2)

There's not a HUGE difference between .0068 & .0078, or .01 & .009, especially when you take into consideration tolerances etc.

***** had to do this as the spacing came out funny.  If this is wrong just ignore me, my head feels like it's been hit with a sledge hammer at the moment and I can barely remember my own name!

[idlefaction]

hehehe tequila...?   :twisted:

yeah that's a definite option...  i can make the middle setting the highest, and have 'normal' as up and 'bass' as down.  but i did that with a rangemaster for a guy and had to take away one of the options in the end cos he brought it back twice complaining that one of the settings was broken...  it just didn't make any sense to him that the sound would get lower up AND down.  

ahhh the joys of customer service.  

[gez]

i did that with a rangemaster for a guy and had to take away one of the options in the end cos he brought it back twice complaining that one of the settings was broken...  it just didn't make any sense to him that the sound would get lower up AND down.  

Just tell them it's 'custom wired', only a few in existance with this option (a collector's item!), charge ten dollars more and send them packing...

[gez]

i can make the middle setting the highest, and have 'normal' as up and 'bass' as down

Mount the switch sideways instead of up/down and you'll have normal (left) high (middle) and low (right).  This might make the switching feel more intuative?