[sdiy] non-mechanical switching solutions

[Jean-Pierre Desrochers]

Rick,

I read you don't have room for rotary switches but if you
finaly find enough space,
for my Moog 904A,B,C clones trio I used the following rotaries:

4 poles - 3 positions Rotary switch 904A:
http://www.arcenson.com/projects/Modular/M104A_Lowpass_Filter_Moog_904A_clone/Specifications/Rotary_switch_for_Moog_904A.pdf

6 poles - 2 positions Rotary switch 904B:
http://www.arcenson.com/projects/Modular/M104B_Highpass_Filter_Moog_904B_clone/Specifications/Rotary_switch_for_Moog_904B.pdf

16 poles - 3 positions Rotary switch 904C (9 of the poles used..):
http://www.arcenson.com/projects/Modular/M104C_Filter_Coupler_Moog_904C_clone/Specifications/Rotary_switch_for_Moog_904C.pdf

They are not that big and easy to find...

JP

******************************************************************


Le 2016-06-28 03:19, Rick Jansen a écrit :
> There are very very small reed switches, and if you wind a coil with
> enough threads the current is quite low. It was just a thought.
> 
> rick
> 
>> On 27 Jun 2016, at 22:46, jays at aracnet.com wrote:
>> 
>> One thing to keep in mind when using relays is unless you are using 
>> latching relays you will need current to keep them in the proper 
>> state. Latching relays usually take a pulse, go to a state and stay 
>> there without the current until the next pulse puts them in the next 
>> state.
>> 
>> Jay S.
>> 
>> 
>>> On 2016-06-27 13:21, Rick Jansen wrote:
>>> Miniature reed switches? Sort of mechanical, but hey.
>>> rick
>>>> On 27 Jun 2016, at 16:15, Pete Hartman <pete.hartman at gmail.com> 
>>>> wrote:
>>>> I have a problem I'm trying to solve....
>>>> ...and let's just assume the problem has to be solved, I can't just
>>>> redesign around it.  In a perfect world ... but that's not where
>>>> this sits.
>>>> I'm working with a ladder filter, switching 3 different capacitor
>>>> ranges (Moog 904A, yes?).  But I don't have room for a multipole
>>>> rotary switch of the necessary size.  What electronic solutions
>>>> might I use for this?   (and note that while step one is to solve
>>>> four poles for the 904A, step 2 will be to solve for the 904C which
>>>> has a *9 pole* switch, which hopefully can use the same solution)
>>>> If I use an on-off-on switch, pull ups and ground connected to the
>>>> common, I have three positions giving me 01, 11, and 10 which can be
>>>> decoded to 3 out of 4 positions on a mux or a decoder.  A Mux acting
>>>> as a switch to put in or out the various capacitor values....
>>>> First thought: CD4052, but that doesn't work well in practice at
>>>> all.
>>>> Second thought: DG409, better characteristics, but that still
>>>> doesn't work sufficiently well.
>>>> Dig around a while for why.... aha, the on resistance for both is
>>>> significant, especially for the capacitive stages of a ladder
>>>> filter.  The DG409 has on the order of 100R - 120R.  Too much, and
>>>> confirmed to be the issue by comparing physical connections with
>>>> wire to physical connections with 100R resistors.
>>>> Third thought: MOSFETs have low on resistance....  And an initial
>>>> test of VN0104's (on resistance on the order of 3R - 5R, much
>>>> better) shows somewhat more promise.  A little concerned about on
>>>> capacitance and also whether I can get an appropriate Vgs at the top
>>>> stage of the ladder (where the source voltage will be on the order
>>>> of 10V), but so far so good; may need a MOSFET with a lower range
>>>> for Vgs-on, but the VN0104 is pretty darn good with a max of
>>>> 2.4V.... that's just at the edge of the spec though, I think,
>>>> something better would be nice.  Don't want to be in the position of
>>>> having to "select" working transistors for the top stage.
>>>> So the questions for the assembled brains bigger than mine:
>>>> 1) can anyone suggest a better (yet still reasonably common) mosfet
>>>> with low Vgs and low rds-on?
>>>> 2) some other (electronic, not mechanical) solution that would work
>>>> in this specific instance?  Note that while the above description
>>>> assumes an SPDT switch, I can go up to 2 poles, but not beyond.  An
>>>> on-on-on would also be an option.  Toggle switch is a requirement
>>>> though.
>>>> Just to repeat; hopefully this isn't necessary in this audience, but
>>>> some other fora where I occasionally ask questions, I often get
>>>> offered answers that ignore the constraints I'm trying to fit within
>>>> (in this case, no mechanical solution, redesigning to use a physical
>>>> rotary switch is not an option).  "Your constraints are stupid" is
>>>> not a helpful suggestion, yet you might be surprised how often it
>>>> comes up :).
>>>> Thanks...
>>>> Pete
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