[sdiy] non-mechanical switching solutions

[Pete Hartman]

Not really :-D

But not really feasible either.

I'll keep it in my back pocket just in case....

Pete


On Tue, Jun 28, 2016 at 2:32 AM, Roman Sowa <modular at go2.pl> wrote:

> And here's the craziest idea ever:
>
> Use a bunch of tiny reed switches, you can find them even as short as 5mm,
> and control them with neodymium magnet attached to a servo, for example
> taken from DVD drive. A bit complex, but pure electric connection, I would
> dare to say audiophile level. You can do 10-poles switch also that way. And
> no power waste while the're in place.
>
> I guess it falls into "Your constraints are stupid" category...
>
> Roman
>
> W dniu 2016-06-28 o 09:19, Rick Jansen pisze:
>
> 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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>>>>>
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