EEVblog #298 - Dave's Decade Digit Display - USB Supply Part 3

[HLA-27b]

Now this is quite pleasing, absolutely no frills and only 14 leds. Does everything a user interface needs to do and no more.
It currently reads 5.70 Volts
Pressing the encoder button toggles between Volts and Amps
The scale can be used as 60mm straight edge and don't worry about the knob height as it does not go any higher than the screws.




The case used is http://www.digikey.com/product-detail/en/1591MSBK/HM361-ND/284747
This is a far better case because it does not have side cut outs.

[EEVblog]

Now this is quite pleasing, absolutely no frills and only 14 leds. Does everything a user interface needs to do and no more.
It currently reads 5.70 Volts
Pressing the encoder button toggles between Volts and Amps
The scale can be used as 60mm straight edge and don't worry about the knob height as it does not go any higher than the screws.

How do you know the absolute position of the rotary encoder?
How can you get a grip on the knob?

(awesome graphic BTW, and I like the concept)
I was going to greater than 12V too.

The case used is http://www.digikey.com/product-detail/en/1591MSBK/HM361-ND/284747
This is a far better case because it does not have side cut outs.

Not having side panels is a big down side. You have to get the case punched. Unless you use the top side mount USB connector and vertical binding posts that I did in my prototype. I've been there, I've costed it and considered it long ago, it wasn't the cheapest solution IIRC.
And the rotary encode and knob make the height much bigger than needed.

Dave.

[HLA-27b]

How do you know the absolute position of the rotary encoder?

some sort of absolute encoder, BCD, Gray code, anything..

How can you get a grip on the knob?

Put a big coin or 2032 on the table and try to rotate using thumb and index finger, it is actually quite ergonomic.

(awesome graphic BTW, and I like the concept)
I was going to greater than 12V too.

NP here,  rinse and repeat as needed.

Not having side panels is a big down side. You have to get the case punched. Unless you use the top side mount USB connector and vertical binding posts that I did in my prototype. I've been there, I've costed it and considered it long ago, it wasn't the cheapest solution IIRC.
And the rotary encode and knob make the height much bigger than needed.

I would much prefer to punch it out. Simply get your hands on something like this and ask a machinist friend to make you the punch(es) that you need from tool steel (you need a machinist friend for this to work). After that any hole in any panel becomes a single 3 second operation for you.
Otherwise you have 3 different panels which still require assembly. Also the seam points where these panels touch each other will be a weak spot. They will flex and squeak and reduce the rigidity of the whole thing. Your customers will notice it.  Actually it might be possible to devise some sort of finger joint to remedy that but why complicate your life and run the risk of increased returns?

[Psi]

I do quite like that design.

[nitro2k01]

I don't know if anyone has mentioned it, but color coding!! The complex variant of this is to have one color for each of the 9 digits, somewhat matching the resistor colors used on hole mount resistors. The less complex option is to give (for example) even digits red LEDs and odd digits green LEDs. This should reduce the "seek time" when having a quick look at the readout.

Since my post seemed to go unnoticed, I'll try again ^^^^

Someone mentioned using green/yellow/red or something like that, like an audio level indicator. In my opinion, that's just fancy but useless. My suggestion would, I believe, cut down the split second it takes for you to find to the right digits, because the color tells you something about the digit.

[PA0PBZ]

I do quite like that design.

Me too, but I can see a few problems, for example how to switch from V to A? I guess you could push the knob if you can find a BCD encoded rotary thing with push capabilities...
But what's worse is, how are you going to read the momentary value of the current? A motorized knob? 

[dcel]

     Build the DDDD up and let us see what it looks like. Spin one with an LCD as well, 7seg or dot matrix. Lets see the resulting feedback on each version. You have to build something that will sell, if everyone responding doesnt like it, it probably wont sell. Yes, you can only make some of the people happy some of the time, not everyone happy all the time.

     Ive built and owned a binary clock and I can say that it doesnt take long to train oneself to know what time it displayed. That is time, and you may have the time to determine what time it is, but standard 7seg clock is much faster to "read".

     I want to know the amount of current being drawn "instantly". I finally own a power supply with voltage and current displays and I really like knowing at a glance what the output is, and I REALLY like having constant current mode. Would I buy another power supply without these features? No! And I am actively looking for another PSU to complement the one I have, just higher current. Yes, a small USB PSU would be nice to have, provided the feature set is there. Do I want a uSupply? Hell yes! That unit has great features, provided you dont try cost cutting it down to a price point.

Chris

[blackdog]

Hi,

Just to make things clear...

The max power of USB-2 is 5V 0.5A = 2,5Watt
Efficiency of DC to DC is approximately 75%
The no load current is in the range of 50mA, already 10% of Max.

If Dave is using a 5V to 24V converter the max output current will be less than 100mA
If he is using a 5V to 15V converter the max output current will be less than 150mA
There will never be 0.5 or 1 ampere range. ( not with a cheap DC to DC )

Dave can you shine some light on wat type of DC to DC Converter is used?

Kind regarts,
Bram

[HLA-27b]

I don't know if anyone has mentioned it, but color coding!! The complex variant of this is to have one color for each of the 9 digits, somewhat matching the resistor colors used on hole mount resistors. The less complex option is to give (for example) even digits red LEDs and odd digits green LEDs. This should reduce the "seek time" when having a quick look at the readout.

Since my post seemed to go unnoticed, I'll try again ^^^^

Someone mentioned using green/yellow/red or something like that, like an audio level indicator. In my opinion, that's just fancy but useless. My suggestion would, I believe, cut down the split second it takes for you to find to the right digits, because the color tells you something about the digit.

I like drawing. What I don't like is writing 

[EEVblog]

Dave can you shine some light on wat type of DC to DC Converter is used?

I showed it in the housing video, a standard 2W SIP 5V-5V isolated converter.
You don't need any more than 2W to make use of the full 500mA USB, as the converter is only 80% efficient at best, meaning 2W output maximum.

Dave.

[Psi]

Here's a quick and dirty mockup of the side led idea i described earlier

It would work best with really wide angle leds, However you would get some back scatter from the rear of the adjustment led

[Madsaaby]

--I rather like Madsaaby's idea for the display, but I am puzzled why it reads from right to left, instead of from left to right.

That's a good question actually Didn't really think about it, think I did it this way because LSD used to be to the right.. But it is kind of reversed compared to how we read things usually, when I think about it. Maybe it would be better to flip it..

- Mads

[HLA-27b]

Here's a quick and dirty mockup of the side led idea i described earlier

It would work best with really wide angle leds, However you would get some back scatter from the back surface on the adjustment led

Nice but surface mount things might peel off in use. Imagine that the user puts it in his backpack together with a bunch of other tools - screwdrivers, side cutter soldering iron etc. etc. Chances are that a few leds might be missing when he pulls it out again.

[hlavac]

There is supposed to be a clear perspex plate over the thing, no?

[Psi]

Yes, LEDs will be protected. The case Dave plans to use will have a transparent top screwed to it.
The tack buttons will be much taller than in my pic and protrude through holes in it.

I actually found a STEP model of a clear case i could import into Altium for the 3D view, but then i remembered that all models in summer 09 are solid. I could do it with an extruded box i guess.

[HLA-27b]

Yes, LEDs will be protected. The case Dave plans to use will have a transparent top screwed to it.
The tack buttons will be much taller than in my pic and protrude through holes in it.

I actually found a STEP model of a clear case i could import into Altium for the 3D view, but then i remembered that all models in summer 09 are solid. I could do it with an extruded box i guess.

Could you export the PCB in some 3D format? I'd like to try it  with transparent box in SolidWorks.
STEP IGES etc. should be fine

[eternal_noob]

Yes, I think it needs to be prototyped and used in person to see how well it actually works in practice.
I think those poo-poo-ing the idea outright sight unseen are maybe being a bit close minded (but I understand their reaction). It could very well suck of course, but then again it may not and be quite usable.

Dave.

I have tried this solution for a simple turns/event counter and it worked out just fine. The first glance at the display is admittedly a little bit troublesome, but in a PS where you know what number is going to be displayed next, by turning a knob either up or down, it is NOT really a problem. Thats because your brain already know where you were AT. Of course, I would never have used this solution, lets say in a bench volt meter. That will suck bigtime!
But anyway, I will warn against using type of display. People tend to choose form over function, not function over form, and those who do will almost hate you for doing this ''gruesome'' thing to them.

[free_electron]

Yes, I like that. But knobs have been vetoed on this design,

What about edge rollers ? They exist in encoder form. Panasonic makes those ( amongst others ). Digikey has em. Behave like a rotary encoder and include the push feature.

Remember old style transistor radios with the little wheels sticking out the side. You would roll over them with your thumb. That's what i'm talking about. They exist as encoder.

As for cheap lcd Look for a COG type display. You could even go for a 3310 style cellphone display. These are dirt cheap on ebay.

[Psi]

Yes, LEDs will be protected. The case Dave plans to use will have a transparent top screwed to it.
The tack buttons will be much taller than in my pic and protrude through holes in it.

I actually found a STEP model of a clear case i could import into Altium for the 3D view, but then i remembered that all models in summer 09 are solid. I could do it with an extruded box i guess.

Could you export the PCB in some 3D format? I'd like to try it  with transparent box in SolidWorks.
STEP IGES etc. should be fine

I found an option to do it. There is an opacity slider i didn't notice.

Here's a few model exports, in case you want to have a play.
I've not checked exactly what got exported though.
http://psi.abcom.co.nz/models.zip

Here's the updated example with a case and cover.

[EEVblog]

What about edge rollers ? They exist in encoder form. Panasonic makes those ( amongst others ). Digikey has em. Behave like a rotary encoder and include the push feature.

Remember old style transistor radios with the little wheels sticking out the side. You would roll over them with your thumb. That's what i'm talking about. They exist as encoder.

I've used those.
Think I briefly considered them on an old proto I think, but they don't really offer any major advantage over tact buttons, and you have to have a cutout slot on the side of the case for them, unless you can mount them on the case end. Devil is in the detail as always.

As for cheap lcd Look for a COG type display. You could even go for a 3310 style cellphone display. These are dirt cheap on ebay.

They are usually not designed for nice rigid PCB mounting. And many physical variations exist that can cause supply headache. The good ones like from Newhaven are not cheap.
I have found 8x2 character based displays cheap, but they are really thick and the bezel will have to protrude through the front panel.

Dave.

[MagFlux]

Dave, your original idea is still the best seen here so far. You may want to play with the LED spacing to get an idea on how well the eye can detect a discernable pattern. I believe that after using it for a while it would be like reading an analog meter by seeing a postion (or pattern in this case) rather that a number. If you want to get more precise silk screen a grid with the number values over the coresponding LEDs.
This silk screen should be on the back side of the front panel and the panel as close to the LEDs as possible.

[EEVblog]

Dave, your original idea is still the best seen here so far.

I think my idea has been pretty comprehensively shot down in flames. Based on all the comments and feedback, hardly anyone wants it or thinks it's a good idea.
I suspect that an LCD solution is the only way forward.

But even if I change the LCD, I'll likely still get hounded on the case  , although no one has yet come forward with a suitable alternative that meets the criteria, and I have not found one myself.

Dave.

[Psi]

But even if I change the LCD, I'll likely still get hounded on the case  , although no one has yet come forward with a suitable alternative that meets the criteria, and I have not found one myself.

What about the small red one of these http://www.hammondmfg.com/1553colors.htm

With nice rubber sides and enough room to mount an LCD on the top yet thin enough to fit into a laptop bag.

Even comes in a nice uCurrent style red according to the website (although the Digikey pic of it is a totally different red so i dunno which red is correct ? )
$4.34 in qty 500, so more expensive than your other case, but it is really nice.
http://www.digikey.com/product-search/en?x=0&y=0&lang=en&site=us&KeyWords=HM1149-ND

[EEVblog]

What about the small red one of these http://www.hammondmfg.com/1553colors.htm
With nice rubber sides and enough room to mount an LCD on the top yet thin enough to fit into a laptop bag.
Even comes in a nice red (although the Digikey pic of it is a totally different red so i dunno which red is correct ? )
$4.34 in qty 500
http://www.digikey.com/product-search/en?x=0&y=0&lang=en&site=us&KeyWords=HM1149-ND

About 3 times the price of my current one, and bigger.
The top must be machined out for the LCD.
Not tall enough to be used as half case.
Only one end removable, so the other end for the USB connector has to be machined out.

No joy.

Dave.

[MagFlux]

Dave, my response to critics that may not like it because "it's different" is as follows...
"Damn the torpedoes, full speed ahead"
However if you are somewhat convinced by them, let's move on.
Regarding the switches, can you price justify a micocontroller with touch capability and
do without mechanical switches and have touch pads instead?
The design would be free of moving (read breakable) parts and be easier to place where you want them.