Rotary switch alternative using a led driver

[radiance]

Hey all....would like to pitch an idea.

My project (an aux expander card for the Buchla 208) needs a 8 position rotary switch.
Thing is: this will not fit on the card.

As alternative I was thinking the following:
Use a small 9mm pot to send a voltage into a led driver(LM3914) in dot mode, which then (instead of a led) drives 2 CD4066 switches, all SMD off course...

Might there be a more elegant solution?

 

[pvision]

Pushbutton to step through 8 settings via a shift register, each with an indicator LED?

 

[radiance]

Pushbutton to step through 8 settings via a shift register, each with an indicator LED?

That's a nice idea!

 

[ruffrecords]

Sounds like a job for a 14 pin PIC.

Cheers

Ian

 

[gyraf]

The 3914 runs its output as series currents, hard to translate to individual switchings unless you use optocouplers

 

[moamps]

A typical application of IC LM3914 shows individual output control. If LEDs are replaced by resistors, the outputs can be IMO used to control TTL or CMOS logic circuits (inverted logic, low voltage means logic "1").

 

[JohnRoberts]

shift register... just clock it one step at a time...

JR

 

[sahib]

If you can accommodate 12.5mm diameter, Elma has one. I have one pole 16 position version but it also comes in two pole 8 position. Naturally not cheap but Grayhill may have similar cheaper.

Otherwise among so many options, a 3 bit binary coded rotary encoder and 1 to 8 mux such as 4051 will also be an easy job.

 

[ruffrecords]

NKK make a small 1 pole 12 switch that is cheaper then ELMA and Grayhill:

https://uk.farnell.com/nkk-switches/mrk112-a/switch-sealed-sp12t-0-4va-28v/dp/1524321?st=mrk

Cheers

Ian

 

[gyraf]

A typical application of IC LM3914 shows individual output control. If LEDs are replaced by resistors, the outputs can be IMO used to control TTL or CMOS logic circuits (inverted logic, low voltage means logic "1").

Agree - sorry, I mixed up with the UAA180

 

[dai h.]

dunno if it's suitable but Tosoku make a 9mm square one (MR8A series) :

http://www.tosoku-inc.co.jp/en/product/rotary.html
(datasheet: )

http://www.tosoku-inc.co.jp/en/product/pdf/rotary/mr8a.pdf
IIRC I've seen one sold on some US site supplying parts for CNC machines (and it was expensive ($50?)).

 

[moamps]

Agree - sorry, I mixed up with the UAA180

The good old UAA170 and UAA180..

 

[radiance]

The rotaries are definitely not an option.
Shift register is cool! Will look into that.

My suggested option of a 9mm pot > LM3914 > 2 x CD4066's has the advantage of instant control. You don't have to step through the register.
Also, the 9mm pot can be a CV input...

Designing these aux cards is a real puzzle. You have to deal with current draw (try to stay below 60mA per rail) , real estate (9cm x 16cm), parts costs and availability (100% price hikes, lead times of up to 1 year).

Here a photo of my previous card design, the sequencer aux card. This one has the option to switch between 8 or 7 steps by means of a toggle switch.

 

[ruffrecords]

The good old UAA170 and UAA180..

Are these still in production?

Cheers

Ian

 

[moamps]

I'm not sure, but I think they are outdated and no one makes them anymore. They can still be found on eBay.

 

[ruffrecords]

I'm not sure, but I think they are outdated and no one makes them anymore. They can still be found on eBay.

Yes, I saw some on eBay. As a device they look ideal for a 12 segment display running from a 12V rail (the heater supply in my mixers!) which is why they interest me. Prices seem to vary alot from a few quid from China to over £20 each from some European sources. Makes you wonder about the provenance.

Cheers

Ian

 

[FIX]

I actually did that once with exactly what you suggested, for a de-esser I designed, it used the led driver into get switches. The nice thing was it could go up or down.

 

[Ilya]

PIC with a rotary encoder can do the work easily. And draw very little current.

 

[radiance]

PIC with a rotary encoder can do the work easily. And draw very little current.

Could you elaborate on this? I think I get it, but it's all quite new to me...
Can you point me to a specific part / pic? Or a data sheet maybe?

 

[warpie]

Also interested in the PIC solution.