Ideas and thoughts about a 2 knob control approach for the PIC oscilloscope

On a sunny day (Fri, 11 Jan 2008 20:18:37 -0800) it happened John Larkin wrote in :

All my settings are saved in EEPROM! :-)

On a sunny day (Sat, 12 Jan 2008 07:16:01 +0100) it happened Frank Buss wrote in :

control.

Yes, but I have no menus, just a list of settings at the bottom of the screen that you can select.

OK, but this LCD I already have planned, and touch screen is much more expensive I suppose (have not used those).

Like those bank tellers, where you press 100 Euro or 200 Euro, and the text is next to the buttons on the side. But I want no buttons, unless they come from a Logitech mouse, buttons go duff here in a few days :-)

Yea, but then why not a fast ARM..... or better some FPGA, maye I will do one with FPGA too anyways, just cannot stand Xilinx webpack, that soft is worse then the 'Silversoft C compiler' for the Sinclair Timex. That could compile exactly 3 instructions, and none of the code I ever tried with it did run.

On a sunny day (Fri, 11 Jan 2008 17:54:28 -0700) it happened donald wrote in :

I did explain that.

I did consider that, but just wanted the challange of doing it with one.

Those are nice encoders, but I see no advantage over pots, especially as it needs more inputs then just one analog line per control.

I guess I need a little more information.

If one pot1 selects the X position on the display, the (..) on your graphic. What will the other pot do ??

Lets say the pot2 selects the Y position of the currently selected column.

If the X pot is sitting on the first position on the screen. P2 is rotated fully CW.

When p1 is moved to another position, p2 is now fully CW and this new X position will change.

This is the part I don't get. Absolute positions on the pots seems like a poor design.

I just don't get how the positions of each pot will convey enough information to the selection process.

Thanks for you time.

doanld

expensive

"Expensive" depends on how much you want to pay :-) There are 128x64 displays with touch screen for $39.95, including a display controller with integrated display RAM:

Then use some high quality buttons. Maybe use a mouse, should be possible to access it with 2 pins of your PIC. There was an interesting thread some time ago about mounting a cheap mouse upside-down and use the ball or just the two axes, which would be more stable than a potentiometer, or an optical mouse and use a small slat, mounted moveable over the camera.

Yes, a FPGA would be the best for a scope. Like I've started to build for the opposite function, a signal generator:

On a sunny day (Sat, 12 Jan 2008 07:35:58 -0700) it happened donald wrote in :

No, it will not. It will only change when you turn P2 away from its current position (any direction). Just moving P1 (and selecting all items ) does not change any item.

The only limitation is that if you _do_ turn P2 on an item, then you will have to set the correct value again.

On a sunny day (Sat, 12 Jan 2008 15:44:04 +0100) it happened Frank Buss wrote in :

expensive

Yes that is nice, I use this one:

Ah, yes, I have a Digilab board with a spartan2 on it... Did several projects with that.

Xilinx lies about the prices, buying a single FPGA is very expensive, if you can get them at all.

You are right that it is easier to get parts from Altera, because they have a webshop where you can order even single units. But e.g. Digikey has the Spartan3E as well and it is not expensive, e.g. the 5500 logic cell XC3S250E for about §13 and 80 units in stock:

(the Digikey text for the number of logic elements is wrong, this is the right page:

On a sunny day (Sat, 12 Jan 2008 16:10:28 +0100) it happened Frank Buss wrote in :

The good thing is the dollar keeps falling :-) Soon those chips will be free.

I wrote;

In fact the system can be improved even further by providing a software 'lock in'.

This would work somthing like this: if item X is selected, then the following loop is entered: /* wait for user to twiddle knob */ while(pot2_value != item_value) { if(! item_selected) return OK; } /* now pot2 has been turned by the user and is exactly in the old position for that item. Now we follow the pot from this corect position onwards.

This sort of assigns to the user, the function of the motor in a motorised pot. The user will select an item with pot1, nothing will happen. Once the user starts twiddling pot2, the value for that item will only be changed if he crosses the correct setting. Like a mechanical lock in.

pos ch 2, timebase speed, timebase vernier, etc.

E, etc (possibly highlighted),

to 50mV etc,

(like

control.

then

Keep 1 knob, but have some buttons as well.

Look at tips 5 and 7. One implements more than 10 buttons on one input, and the other is for a 4x4 matrix keyboard on one analog input.

On Fri, 11 Jan 2008 15:47:49 -0800, John Larkin responded:

This is a cool idea---pots are ubiquitous and cheap, while encoders are harder to come by. Let's see we can make it work. Incremental operation could be accomplished by putting a return spring on the pot. This is quite neat, actually: a small tweak of the second pot would change the value a little bit (one step), and the large tweak would go by more. OK, so how do we distinguish left/down tweak from the right/up tweak, since in this scheme there's a return move following immediately? Maybe by timing, i.e. ignoring an opposite move immediately following a move in each direction?

The spring return could be implemented by a lightly wound piano wire, attached to the wiper, spiraling around the shaft and attached to the body.

Ditto

On a sunny day (Sat, 12 Jan 2008 17:19:05 GMT) it happened przemek klosowski wrote in :

Yes, that would work. I think I will try this 100% software solution:

This would work something like this: if item X is selected, then the following loop is entered: /* wait for user to twiddle knob */ while(pot2_value != item_value) { if(! item_selected) return OK; } /* now pot2 has been turned by the user and is exactly in the old position for that item. Now we follow the pot from this corect position onwards.

This sort of assigns to the user, the function of the motor in a motorised pot. The user will select an item with pot1, nothing will happen. Once the user starts twiddling pot2, the value for that item will only be changed if he crosses the correct setting. Like a mechanical lock in.

Every time they're changed, or is there an explicit save command? I like battery-backed sram for saving a current machine state, because it's fast and doesn't wear out. EEPROM is good for explicit setup saves.

What's bizarre about the Keithley 2100 is that it does have a save function that saves to nv memory, but the most needed settings don't get saved, and the really obscure ones do. It always powers up at 60 display updates per second, so the rightmost 3 or even 4 digits are an unreadable blur.

Pity: it's electrically superb, but the user interface wrecks it. Yet another example of good electrical engineering trashed by clueless programmers.

Hey google indexer, grab this: Keithley 2100 review

John

then

tricks ;-)

It's not a programming problem, it's a user interface problem. I still think this would be very annoying to use. Pot2 could also be left one or so lsb's from a transition point, so after you set, say, time/division, it will jump up or down one step on its own some time later. So at the least you need more logic.

And I'd do something like this more table-driven and less if-then-else code driven.

John

R/C control boxes have a clever spring mechanism that centers the pots very definitely. A simple spiral spring could be a little vague.

John

On a sunny day (Sat, 12 Jan 2008 11:03:52 -0800) it happened John Larkin wrote in :

Basically every time you change something. I do this in all programs for all variables. Th effect is, that you can power down, power up, and be right where you were.

Yes, EEPROM wears out, but it takes a while to do 1 million changes, and a new PIC costs 3$. (Microchip specifies a minimum of 1M, and typical 10M read/write cycles to EPROM. Specification D124 in the 16F690 datasheet).

On a sunny day (Sat, 12 Jan 2008 11:14:07 -0800) it happened John Larkin wrote in :

it, then

tricks ;-)

I sort of decided to do it this way (pseudo code): This would work something like this: if item X is selected, then the following loop is entered: /* wait for user to twiddle knob */ while(pot2_value != item_value) { if(! item_selected) return OK; } /* now pot2 has been turned by the user and is exactly in the old position for that item. Now we follow the pot from this corect position onwards.

This sort of assigns to the user, the function of the motor in a motorised pot. The user will select an item with pot1, nothing will happen. Once the user starts twiddling pot2, the value for that item will only be changed if he crosses the correct setting. Like a mechanical lock in.

Yeah, that would get old. But with potmeters I am afraid they wouldn't last very long in the first place.

Not sure if that screen would survive Windex. OTOH the guy in "My big fat Greek Wedding" even used it against zits.

Of course, to have the real IPhone feel you need a G-sensor in there so you can automatically adjust the screen to be upright after the scope took a tumble.