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 Post subject: Two SPST push buttons to knob SPDT control?
PostPosted: Dec Thu 05, 2019 11:35 am 
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Joined: May Fri 10, 2019 1:17 pm
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Location: Bedford, IN
I've been playing around with making a new wood tombstone cabinet (or cathedral) styled radio using a new solid state stereo radio donor as the internal guts base (and adding in a pre/amp/Bluetooth/Aux/etc). I blame the idea on some of those 80s/90s radio reproductions that I've picked-up cheap recently, but sound bad typically not worth modifying directly. I thought what if some effort and quality was put into such a reproduction radio - then the project was started.

Many possible new radio donor base systems however typically use two buttons each for tuning and the volume though (there are a few with knob control (potentiometers or rotary encoders) or almost nearly only remote controlled in receivers). A used radio is a option, but any I've considered such as a GE SuperRadio II or such are ones I'd rather not sacrifice on a project, and need to find reasonable access to more of the model as I plan to make a few.

I'd like to keep the classic look and use a knob that self-centers with momentary contacts, turning the knob left pushes a switch, and turning to the right pushes a second switch. The knob control switches would be connected to the donor radio system's switches, keeping the style and use of knob control.

An example of what I mean...
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knob-switches.png
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After many hours of searching for a solution I am left with buying some $100+ per switch option that may not work, have some made custom at even higher cost (Grayhill), or a very limited stock from China of questionable use/quality/stock.

Some ALPS rotary switches seem to fit the bill, "ALPS Dual Concentric Momentary Spring Return Rotary Switch w Push Switch" but there are only a few available. The part number given also isn't referenced in any ALPS databases so likely a clone/fake and no way to find more stock.

Another switch I found is a "Black Rotary Switch 3 Position Spring Return" at about $18 per switch and $35 for shipping. I figured I could replace the knob (one way or another), but after seeing the total costs I'd just live with push buttons... such as using a momentary SPDT rocker switch mounted sideways for control.

The last solution is to use EC11 rotary encoders (or similar) programmed with a Arduino with switched outputs to the donor system switches solder pads. While it is said to work for my problem, a Ardunio Uno R3 clone with all the controls/parts would be under $20 total, it isn't a buy and solder solution. I've never used Arduino so I'd have to learn the system/usage/language, then write the sketch code needed for the control functions (hopefully they have good libraries for the code already), which will be a long process I'd rather avoid - but at the moment the best solution.

Does anyone else know of part number of a suitable momentary control under $10 per control switch, a method to hack/hobble together a solution, or something else?

I did learn searching online for a solution turned up several others asking the same question and are directed to the Arduino option.

Fitting the tuning dial to a new case is another post and a project in itself. I'm a fan of the early round dial tuners and have been experimenting a bit on a solution. If I use a Arduino in the controls, I can also use it to power a LCD with a round dial displayed to approximate the dial. Or simply scrap the ideas and use a Arduino with a AM/FM/SW radio as my system base using a SI4844-A10-GU solving that problem too.

Perhaps I should just use a tube radio, but I don't want to gut one for a project. Adding a AUX input seems easy enough off the volume pot, but don't have a loose chassis - perhaps I need to look for that instead. :)


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 Post subject: Re: Two SPST push buttons to knob SPDT control?
PostPosted: Dec Thu 05, 2019 6:46 pm 
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I don't have an answer to your specific control question, but I've been thinking of something similar. I want to put one of my antique radios in the guest bathroom because it looks good. Right now I have a big 70s RCA radio with lovely sounding FM. It's ugly and screams 70s, but it turns on instantly.

Contrary to my purist biases, I don't want to have to wait for tubes to warm up. I'm willing to sacrifice my purist instincts to get something aesthetically pleasing with instant sound and without spending $ for a Tivoli.

I came across this $6.99 kit using the famous Sony CXA1191 chip. https://www.ebay.ph/itm/Student-Project ... 2940499167

I have a cheap Fada Bullet repro with that chip and it's sensitivity is remarkable,. However, the repro is way downsized and has a tinny little speaker with no room to add a bigger one. Otherwise it would be a great solution.

BTW, the chip has a builtin audio amp, but would benefit from a proper amp such as this configuration: http://dangerousprototypes.com/blog/201 ... -receiver/

Then the biggest challenge is matching the varicap with the dial.


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 Post subject: Re: Two SPST push buttons to knob SPDT control?
PostPosted: Dec Fri 06, 2019 4:13 am 
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Location: Bedford, IN
Indeed it sounds very similar to my project idea. I admit I far from an audiophile, and my very limited budget would prevent even thinking of it. :lol: I am still a fan of 8-track and cassettes too (born in the late 70s).

I do love putting new music on tape especially when friends/family listen to it. I A/B between the tape(s) with the CD/Record/MP3/whatever and they don't believe their eyes even after I show them, as I have my equipment ran through a switcher and they can't tell what source the receiver audio is coming from. It is amazing what a serviced tape deck with new belts and properly adjusted internally/heads/etc sounds like compared to their memory/perception of a format.

I mention that as I find everyone has a different response to audio quality based from the equipment of course/their hearing/perceived quality based from price/cabinet style or materials/format/etc. I can only imagine even a bad radio in a quality radio cabinet will make many perceive it much better than it really is.

That is a cheap kit to build too that you linked, even if it doesn't work out. Looking at the datasheet for the CXA1191 chip (CXA1619) it can do AM and FM, perhaps with a bit of alterations the kit would do both (complete schematics in the chip datasheet).

I've looked at some myself such as the TA8122, TA2111, TEA5711, and others. Honestly short of building each myself, from parts or a kit, there is no way to tell if any are actually better - perhaps another time as I have a workbench full of projects already.

I found the few reviews for the obsolete or even current production radio chips were too biased from different kit limitations, parts quality, and used different speakers/headphones between them (even if individuals tried several different chips).

That said there is a way to test if someone can really tell the difference from the audio or radios. I myself did automatic ABX blind testing (using the free ABX Comparator add-on for foobar2000 (a great tool for tagging or permanent ReplayGain for songs/albums) with songs I actually listen to done in various MP3 CBR (constant bitrate format) amounts to see where I could stop hearing a improvement. I chose which numbered song I thought was which bitrate and did a average of my results after the test ended and I found out what was what (it does it randomly).

Turns out for music that was typically 192Kb to 256Kb depending on the song/instruments for me, and about the same for my wife. At that point I decided with my MP3's to go to the last step and max out at the 320Kb CBR format, besides that would prevent having to redo any recordings later to improve the audio (unless I want all FLAC). Current I have 56,796 songs in my library at 556 GB in MP3 320Kb CBR, from needle drops/bought from Google Play/Amazon/Apple/etc.

Besides testing for bitrate or pure FLAC audio, APX testing can be used to test various music formats or radios/systems if they are recorded as well (CD/8-Track/Cassette/CD/Records/Tube vs Solid State/different systems/etc).


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 Post subject: Re: Two SPST push buttons to knob SPDT control?
PostPosted: Dec Fri 06, 2019 4:45 am 
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Yes, the CXA1191 can do both AM and FM, as my little Fada bullet repro has an FM/AM switch. As I mentioned, it's sensitive enough not to have multipath problems other radios in my house have.

If you want something simpler and newer, you can get the non-kit Sony SRF-59 transistor radio for $14.95. It is so good that DXers like to mod it, such as installing a big tuning cap. There's no speaker, just a phone jack. The FM quality is outstanding.

****PAUSE*****

Ok, I just looked it up and it's no longer available from the major sellers. YIKES, it's almost $200 on Amazon. Maybe you can find a used one cheap on eBay.

Here's more about it: https://swling.com/blog/2015/10/pocket- ... -srf-39fp/

Ebay has them: https://www.ebay.com/sch/i.html?LH_CAds ... =&_fosrp=1


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 Post subject: Re: Two SPST push buttons to knob SPDT control?
PostPosted: Dec Fri 06, 2019 2:34 pm 
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Location: Boiling Springs, PA
When you arent looking for a circuit you find it but when you need to find that circuit you cant. Somewhere I came across a circuit that performed an up/down function using a pot and a window comparator. Essentially the wiper was connected to one input of each comparator directly and the wiper was also connected to an RC circuit that connected to the tied common inputs. The RC would lead or lag the actual wiper voltage depending on the direction of the pot and the comparators would change states for a time determined by the RC time constant for an up/down control output.

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 Post subject: Re: Two SPST push buttons to knob SPDT control?
PostPosted: Dec Fri 06, 2019 6:08 pm 
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flyboy71 wrote:
When you arent looking for a circuit you find it but when you need to find that circuit you cant. Somewhere I came across a circuit that performed an up/down function using a pot and a window comparator.


Could it be a tracking comparator? https://www.elektormagazine.com/magazin ... 8699/47206

More to what you were referring to, I'll bet one of these circuits could be easily adapted to do your described function:

http://www.bowdenshobbycircuits.info/window.htm


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 Post subject: Re: Two SPST push buttons to knob SPDT control?
PostPosted: Dec Mon 16, 2019 7:08 pm 
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Joined: Sep Thu 23, 2010 6:37 am
Posts: 12017
Location: Powell River BC Canada
Debounce circuit is a tricky situation.

How about a simple shaft attached to a tiny mirror directing light from a LED ).

To the left it shines on one photo transistor, to the right, on another.

Those are open collector.

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