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Topic: Single digit, Seven segment Numitron program and pcb design needed. (Read 13342 times) previous topic - next topic

Daddyfredregill

I love to make cool things, I do wood working, metal working. What really stumps me is programming and board design. I am looking for someone to program and design me a project. I am wanting to build a wristwatch with a single numitron display. Here is a very similar project that someone else has done.

https://hackaday.io/project/7881-micro-numitron-clock

This build is very similar to what i need but my numitron display is a little different. It needs higher voltage than the one he uses. Basically i need something like this that is very small and will work with my display.

Here is the specs on the display i am using.





Thanks for anyone that can help

wvmarle

The dimensions of that display - 0.45 x 0.87 - is that in inches? And you want seven of those to form a wrist-watch? And I thought my wrists are pretty big...

Need more details to understand what you really plan to do.
Do you have any schematics?
What components do you expect - microprocessor, display driver, RTC?
Power source?


Quality of answers is related to the quality of questions. Good questions will get good answers. Useless answers are a sign of a poor question.

Daddyfredregill

Not seven of them. Just a single display and it tells time in sequence one number at a time.

I also have no idea what to do on the pcb/programming side of things.

The link I provided is almost what i need. His build has an RTC, microprocessor, super capacitor to keep RTC memory. All of this stuff he has in an inch size pakage.

The build in the link almost fits my needs just not quite the same. The build lists all the parts and code. Like I said I am looking for someone that can do the whole thing at a price of course.

Without a community to help there is no chance of me getting this done.

Thanks

wvmarle

You have the components already?
How many sets do you want to build]?
Just the PCB or with components assembled?
What's the controls supposed to look like?
How to attach to your wrist?
Any casing around it needed?
What kind of connection for the charger?
Probably more questions will come up when implementing the project. Looks like an interesting thing to do to me. You may not have the answers to all of these questions, that's fine. When sending off a design it's quite normal to say "this is important, has to be done just like that, and those things are flexible for you to finalise".
Quality of answers is related to the quality of questions. Good questions will get good answers. Useless answers are a sign of a poor question.

Daddyfredregill

No components, besides the numitron display. Nothing else. Everyrhing is flexible just has to be small. I will design the case aroind the pcb.

wvmarle

Minimum size for the PCB will be about 20x30 mm, provided the supercap and the display are on opposite sides. The other components can be small - an ATmega328 is available in packages of just 4x4 mm. This kind of miniaturisation also pretty much means DIY/hand soldering is out - you'll have to go for assembled PCB and that of course adds quite a bit to the cost due to tooling cost which is really high on a per-piece basis for just a few PCBs.

If you want to be able to solder it yourself, have to go for a bit larger parts. To save space maybe an ATtiny in SSOP packing (0.65 mm pitch can be hand soldered just fine), have to see how can go about programming it on board, the ATtiny is not designed to make that easy.

The two bulky parts are of course the display and the supercap. Those take most of the space.
Quality of answers is related to the quality of questions. Good questions will get good answers. Useless answers are a sign of a poor question.

Daddyfredregill

So how small do you think it could be done with diy/hand soldering.

wvmarle

Well... how confident are you soldering SMD components? Those are the smallest. 0.65 mm or even 0.5 mm pitch on the leads means you're looking through a magnifying glass or microscope (x3 magnification about) to see what you're doing.
0604 size resistors and capacitors are the smallest components I've done, not interested to try the smaller ones.

I think you'll end up at about 25x40 mm, no more. A major factor is how big a capacitor you want on it, those things are bulky, too. I saw a 1 F cap that was 19 mm diameter, 6 mm high. Not much for it's capacitance, yet easily half the size of your display.
Quality of answers is related to the quality of questions. Good questions will get good answers. Useless answers are a sign of a poor question.

Daddyfredregill

I think i could handle smd. If i had some practice. I looked at the ATTiny, it only has 6 outpits i believe. I think i need more. My diplay has 7 correct.

wvmarle

The x5 series has only 6 outputs but others such as the x4 series have 12 I/O.

The x5 is popular as it's one of the few that comes in DIP package... Still, programming them on board is an issue.
Quality of answers is related to the quality of questions. Good questions will get good answers. Useless answers are a sign of a poor question.

Daddyfredregill

So how do you program them? Do you have to make some sort of socket base and hook it up to an arduino to program it?

wvmarle

Indeed - six connections: PWR, GND, RESET and the three SPI wires. Could create a block of six plated holes in the PCB and then you press pogopins in it to make the connection. A regular Arduino can be the programmer; I've used a Pro Micro for that purpose. The problem is that connecting LEDs to the same pins will likely mess up the signals.

You have 12 I/O of which one is the RESET, so effectively 11.

Seven for the display, reserve three for the SPI part, one button (a push button can use an SPI line safely).

Then you also need two for the RTC (I2C - those are normally shared with the SPI lines - should have no problem with programming but not enough experience to say for sure).

I/O:
7x display.
1x push button (to wake up the processor and have it start displaying the time, one digit at a time).
2x I2C.

I2C and the 11th pin are also the SPI (programming) interface. An ATtiny24/44/84 or the 441/841 would be suitable. The latter appears to have I2C slave built in (have to read the datasheet better - it'd have to be able to act as master and slave in this situation).

To be sure you can keep the time, an RTC can come with battery backup. That adds a small battery to your device, but at least you don't have to reset the clock (unsure how - maybe some trickery with Serial or via the I2C bus which would be available through the programming contacts) every time the supercap runs dry. Assuming it will now and then.

This is quite a project. Selecting components (and studying data sheets), building a prototype (going straight from design to PCB is of course possible but risky - very hard to make corrections), write software, design & manufacture PCB, getting all components. The final assembly is the easy part, an hour or so of soldering. The first part can easily be 20-30 hours of work. Not building the first prototype saves about 1/3 of that.

Come to think of it, I wouldn't want to send out a bag of parts and software and hope it goes fine. I'd want to have the PCB assembled, software installed - otherwise if something goes wrong it's almost impossible to debug and get working.

Wouter.
Quality of answers is related to the quality of questions. Good questions will get good answers. Useless answers are a sign of a poor question.

wvmarle

Pretty much the minimum size this can be is a PCB the width of the display, and the length of the display plus the supercap plus a push button (approx 40 mm / 1.6 inch).
Quality of answers is related to the quality of questions. Good questions will get good answers. Useless answers are a sign of a poor question.

wvmarle

Another consideration: a 5 F supercap would provide about 10 minutes of power to the display. Those things are huge: 10x20x30 mm, that's 3-4 times the size of the display. A 1F supercap would come to about 21.5mm diameter and 13 mm high, still bigger than the display and able to provide about 2 minutes of display power. Supercaps that fit within the profile of the display max out at 470mF (rated voltage 5.5V), providing barely 1 minute of power for the display.

My power estimate is based on the RC time constant, and that's the time for the power to drop from 5.5V to about 3.5V, which is quite a bit less than the recommended voltage of the display.

The AVR chips are rated to operate at up to 5.5V while the display wants 4.5-6.5V so that poses another issue. You'd want to go to 6-6.5V with the battery to have maximum lifetime but then you must include a regulator for the processor, and drivers (transistors) for the display.

Another question: does this display need current limiting resistors on the segments, like an LED would?
Quality of answers is related to the quality of questions. Good questions will get good answers. Useless answers are a sign of a poor question.

Daddyfredregill

I lit up the whole display to show a number 8. At 4.5v it was readable but 5v to 6v would be ideal. So no resistors if the coltage is between 4.5 and 6v.

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