Knobs instead of touchscreen

[Martinn]

Hi all,

watching Tek 576/577 videos I really like those old school knobs https://w140.com/tekwiki/wiki/576
If one would build a curve tracer these days, it most likely would operate on a touchscreen plus maybe an encoder.

Would it be possible to retain some of that old school usability in a modern instrument? They used those multi gang rotary switches (which apparently were Tek custom and are of course mostly unobtainium now) out of necessity back then, but they give immediate feedback and show you where you're at at a glance. On top there are specialties like the power readout of the combined resistor/voltage knob of the 576.

So I wanted to do a quick test:
- make 2 layer board
- have it assembled by JLCPCB
- use as many basic components as possible (otherwise $3 feeder loading fee for any non-basic component)

I ended up with a board with STM32F103, three encoders (hardware decoded on STM32, four would be possible) and three LED drivers with 32 LEDs each. I tried shift registers first (which would be basic components, so essentially free) but that would need too much space. Eventually I went with a Chinese 36 LED controller (with RGB breathing mode hardware support).
On top, I added 36 0402 LEDs (+$3 again) to mimick that beautiful HP5082 dot matrix display (13 segments per digit). The LED controller can be set to four addresses so with that the I2C bus was full.

Based on the PCB 3D model, I made a light guide/spacer and set of knobs.
The front "film" is printed on paper, would be laminated in a real device. Scale is inspired from the Tek 576 and 177 plugin.

I like the look! On the right encoder, I made a dual LED ring that could indicate voltage and series resistor. The real thing has a mechanical interlock on those knobs: For each voltage, there is a minimum series resistor that you can choose. With encoders, you can't generate force feedback for that, but you can move both scales at once to illustrate limit operation. The encoders have a pushbutton switch, on on the right one, you can switch to the inner scale by pushing the knob (with the 576, it's pulling).

That was just a quick+dirty prototype to visualize the look+feel. Will I use that? Needs a lot of space, but on instruments where you have fixed settings given by the hardware (like with a curve tracer: voltage and series resistor), this might be an option. Of course on remote operation you can show the state on the LEDs.

The HP5082 simulation was messy to layout and needed lots of space. The 36 outputs of the LED driver just gets you to 199. Not impressive. Maybe a star-segment display might be an option - or just plug one of those cheap 1" SSD1306 OLED modules in there. Or point at the main screen...

What do you think?

- Martin

[abeyer]

Can't say I wouldn't sometimes miss the big "thunk" of clicking a multi-gang rotary switch into place... but this looks really nice and I think I'm likely to borrow the approach at some point. Printed & laser cut acrylic might make an even nicer panel instead of laminated paper.

[negativ3]

I prefer physical to greasy marks on glass as well.

Very pretty.

[zapta]

I prefer physical to greasy marks on glass as well.

You wouldn't like the Tesla then ,even the gear shifter and the glovebox open button are on the touch screen.

[Terry Bites]

There's nothing like a good knob.
Touch screens are pain in the a**e.
Even the filthy disgusting vile germ ridden supermarket checkouts hate me.
I hate them right back.

[squadchannel]

need a LED driver? With the 74595, only 3 pins are needed for control. Cascade them for unlimited expansion, and it's cheap.
you were writing down the reason.

I totally agree that the touch panel is shit. 

[jpanhalt]

I have extremely dry skin and find touch screens almost impossible to use. After I couldn't check in for a flight without help a couple of years ago,  I bought a package of cheap  styluses.  They're like my reading glasses, for which I probably have 10 pair spread throughout the house.  It's a scary knowing you can't dial 911 if you lose your stylus.

[Martinn]

need a LED driver? With the 74595, only 3 pins are needed for control. Cascade them for unlimited expansion, and it's cheap.
you were writing down the reason.

Yes, I had the shift register version first. But it's four 8 bit registers per LED ring, plus 32 current limiting resistors. That wastes a huge amount of board space.
Another problem: Modern LEDs are painfully bright. I often use 10k resistors in supply indicators.
I could not try this specific LED in advance, had I chosen the resistor incorrectly, I would have had to exchange 100 or so resistors. Best 0402 to save space.
With the LED driver, there is one reference resistor, one master current register and then individual 8 bit brightness registers for each of the LEDs, all in one QFN package. And while I hate soldering QFN, hand soldering such a board is out of question anyway and as long as JLCPCB does the soldering (and some P&P the assembly) I don't mind.

[Kjelt]

 Saw a cool knob with integrated oled display, you can change the scale on the fly.

[Martinn]

Saw a cool knob with integrated oled display, you can change the scale on the fly.

TSD knob display? https://www.st.com/resource/en/brochure/guide-how-to-get-started-with-tsd-knob-display-and-touchgfx.pdf
Nice, if you manage to buy one.

[Kjelt]

Saw a cool knob with integrated oled display, you can change the scale on the fly.

TSD knob display? https://www.st.com/resource/en/brochure/guide-how-to-get-started-with-tsd-knob-display-and-touchgfx.pdf
Nice, if you manage to buy one.

Yes looks similar. The guy told me he ordered five different versions from different chinese , and european manufacturers to get a good one. Displays are equal but the turn click feel was important to them.
But in your link there is a link to alibaba so I think you can order them on ali.

[Martinn]

But in your link there is a link to alibaba so I think you can order them on ali.

Alibaba link says MOQ 1k...
Found one on Aliexpress https://de.aliexpress.com/item/1005010298802015.html - not sure - but insane shipping costs.

But actually my point was the LED scale, which would both indicate where you are and also gives you an excuse to reproduce those wonderfully ancient Tek front panel graphics.
I did not manage to find out the correct font they used, but I think Atlanta comes close.

[abeyer]

There's also this open source design:

[Obsidianxenon]

For the fact that the multi-gang switches are impossible to find:

You could in theory get a single-gang one and connect each throw to the gate of n transistors (n being the amount of gangs you want), then hook up the common pole to a positive supply.

Practical? No. But you do get the rotary switches.

[squadchannel]

I did not manage to find out the correct font they used, but I think Atlanta comes close.

The font they used at the time was "Univers"(below).

[David Hess]

They used those multi gang rotary switches (which apparently were Tek custom and are of course mostly unobtainium now) out of necessity back then, but they give immediate feedback and show you where you're at at a glance.

Before Tektronix used their custom rotary switches, they used latching push-buttons to drive very small relays, which became today's "telecommunications" relays.  These relays perform well to 100s of MHz and could be used now to do the same thing with a microcontroller operating the relays.  Internally they are constructed with the contacts close to their printed circuit board pins, yielding good high frequency performance.

I tried shift registers first (which would be basic components, so essentially free) but that would need too much space.

Tektronix eventually used shift registers to drive LED displays and relays in their microprocessor controlled test instruments.  Shift registers have the advantage of being able to be located near the circuits they control.

That was just a quick+dirty prototype to visualize the look+feel. Will I use that? Needs a lot of space, but on instruments where you have fixed settings given by the hardware (like with a curve tracer: voltage and series resistor), this might be an option. Of course on remote operation you can show the state on the LEDs.

Another thing Tektronix did before rotary encoders were commonly available was to use potentiometers, including 360 degree dual anti-parallel potentiometers, read out by a processor.  They kept these for a while for analog controls while also using rotary encoders.

[negativ3]

DM13A. 16 channel but single resistor sets current for all leds.

[Terry Bites]

My smart phone is a waste of space too.

[Martinn]

I did not manage to find out the correct font they used, but I think Atlanta comes close.

The font they used at the time was "Univers"(below).
(Attachment Link)

What about the front panel?

https://w140.com/tekwiki/images/6/68/Tek_177_b.jpg

Not sure if this matches.

[Martinn]

DM13A. 16 channel but single resistor sets current for all leds.

I used that one: https://jlcpcb.com/parts/componentSearch?searchTxt=C5125743
$0.62 for 36 LEDs. Single current set resistor (plus tons of registers). +$3 feeder loading at JLC assembly

[Martinn]

Before Tektronix used their custom rotary switches, they used latching push-buttons to drive very small relays, which became today's "telecommunications" relays.  These relays perform well to 100s of MHz and could be used now to do the same thing with a microcontroller operating the relays.  Internally they are constructed with the contacts close to their printed circuit board pins, yielding good high frequency performance.

Another thing Tektronix did before rotary encoders were commonly available was to use potentiometers, including 360 degree dual anti-parallel potentiometers, read out by a processor.  They kept these for a while for analog controls while also using rotary encoders.

Interesting they worked with push-buttons and relays. It would seem that it it pretty straightforward to have custom made multi gang switches. On my AM502 or 503 (not sure which one) there is a set of cams on an axle, which lifts spring loaded contacts off the PCB. Nice design, as long as it works. But with all those custom chips in the 503, the switch will be the least of the problems with a repair.

Anti-parallel potentiometers: I have heard of 90° shifted (sine/cosine) ones for the same purpose. I searched for those, but they have gone fully extinct.

And while we are in the Tek nostalgy mode: I'm sure you know their history of numeric readouts - on the 576 it looks like some fiber optics? My favorite though is the 7000 series analog ROM by Barrie Gilbert https://w140.com/tekwiki/wiki/7000_series_readout_system - I once attempted a discrete replica of that.

[David Hess]

Before Tektronix used their custom rotary switches, they used latching push-buttons to drive very small relays, which became today's "telecommunications" relays.  These relays perform well to 100s of MHz and could be used now to do the same thing with a microcontroller operating the relays.  Internally they are constructed with the contacts close to their printed circuit board pins, yielding good high frequency performance.

Another thing Tektronix did before rotary encoders were commonly available was to use potentiometers, including 360 degree dual anti-parallel potentiometers, read out by a processor.  They kept these for a while for analog controls while also using rotary encoders.

Interesting they worked with push-buttons and relays. It would seem that it it pretty straightforward to have custom made multi gang switches. On my AM502 or 503 (not sure which one) there is a set of cams on an axle, which lifts spring loaded contacts off the PCB. Nice design, as long as it works. But with all those custom chips in the 503, the switch will be the least of the problems with a repair.

They used the relays in the late 1960s, and replaced them with their custom cam switches in the 1970s.  Nobody at the time had high performance relays like that, so Tektronix made their own and they were selling them to others, but they were more expensive and took more space than the cam switches which replaced them.

Anti-parallel potentiometers: I have heard of 90° shifted (sine/cosine) ones for the same purpose. I searched for those, but they have gone fully extinct.

They might have been 90 degree shifted sine and cosine.  They used them in the 2400 series of portable oscilloscopes to good effect.  Considering how much encoder controls cost now, I suspect they would be cost effective even now.

And while we are in the Tek nostalgy mode: I'm sure you know their history of numeric readouts - on the 576 it looks like some fiber optics? My favorite though is the 7000 series analog ROM by Barrie Gilbert https://w140.com/tekwiki/wiki/7000_series_readout_system - I once attempted a discrete replica of that.

The 7000 series was originally intended to use the fiber optic readout system, and has the fiber optic guides molded into the 7000 series plug-ins, but Barrie Gilbert got his system running just in time.  The 7000 readout system had 3 or 4 versions as time went on, with the last one being all digital.  My favorite is the variation which uses short strokes generated digitally rather than the analog ROM version.