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Topic: Single digit, Seven segment Numitron program and pcb design needed. (Read 17155 times) previous topic - next topic

wvmarle

Most of the components I haven't been looking for where to buy, just looking at spec sheets.

1. Where do you get the sot23 chip for the boost converter?
Probably best to just buy the ready-made module for prototyping. Saves work.
I just copied that circuit from the data sheet.

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2. What size is an 18p capacitor?
Small brown disk, 3 mm or so. Probably identical in size to the 100nF ones. But it may need a different value depending on the crystal, depends on the exact part.

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3. Where do I find a flat schottky diode?
SMD you mean? For prototyping, just go for a through-hole part. Easier. The particular types as given in the data sheet are listed on Digikey but only as through-hole part.

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4. I can not find a VSSOP DS1340 RTC, all i can see is TSOP.
According to the data sheet it also comes in VSSOP package. Check for the MSOP instead - that's apparently another name for VSSOP. I see that package on Taobao a lot. But for prototyping it doesn't matter, really.

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5. I do not see an ATTINY441-SSU that is a SSOP
I bough those from Element14 myself.

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6. For the Dual LED can it be 5mm or does it need to be 3mm?
The current rendering is a 5mm LED as apparently they don't come in 3mm size. I was hoping for the smaller size, would fit better.

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7. I want to mix up the colors on the components like the resistors, if they are 1/4w rated will they fit in the same spot or do i have to be careful of length and width?
All standard dimensions. 6.3x2.5mm or so is the standard package. You can of course change the direction of the resistors, but not the order: that's fixed, in a way that makes the PCB design the easiest.

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8. When I am searching for these components should everything be 10v rated or 16v?
The supercap is rated 5.5V.
The other caps should be at least 10V, preferably 12V or more. Higher voltage rating is fine but the parts start to become bigger.
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Daddyfredregill

Thanks for all the info. I am going to try and get all these components together in the next couple of weeks. Then I will get back to you.

Thanks again

Daddyfredregill

I am collecting parts right now. I was looking at crystals and did not know if i needed khz or mhz?

wvmarle

You need a 32.something MHz crystal for the RTC. The processor can run off it's internal oscillator, no need for crystal.
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Daddyfredregill

All the can looking crystals that are the 32 mhz that i find are all to tall like 9mm. I think that is too tall for the display.

wvmarle

Mmm. Interesting, I don't know where I got to the other size before.

The obvious solution is to put it flat on the back of the PCB of course. That makes for one grey element on the front less. The whole thing may become a little thicker, though there's also this supercap on the back.
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

On Digikey I can find very few crystals at that frequency - while I heard before that it's a very common frequency for clocks, that 32.786 MHz.  And only one can shaped and that's the larger size.

Anyway, just now I did a quick Google search on clock crystals, first advert is banggood offering 2x6mm crystals.
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

Of note: this advert lists 12.5 pF load capacitance, so you need 2x 25 pF caps for this. My schematic shows a different value, 18 pF I think. These caps indeed have to be matched with the crystal.
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


wvmarle

Oh my.
Glad you're paying attention :-) You made me re-read the data sheet of the DS1340.

This is what it has to say about pin 1, 2 / X1, X2:
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Connections for a Standard 32.768kHz Quartz Crystal. The internal oscillator circuitry is designed for
operation with a crystal having a specified load capacitance (C L ) of 12.5pF. X1 is the input to the oscillator
and can optionally be connected to an external 32.768kHz oscillator. The output of the internal oscillator,
X2, is left unconnected if an external oscillator is connected to X1.
Indeed that's a kHz, not MHz. And this means the external load capacitors are not needed, either, those are built in into the chip.

So that simplifies the whole thing a bit, good.

And it explains why I saw so very few 32.786 MHz crystals on Digikey!
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


wvmarle

Yes - two caps less. That's it.
On the PCB it allows for a bit more space for the Numitron itself, so it can be moved a bit away from the edge. I now placed it right against the edge of the PCB, now can move it 1.25 mm (50 mil) up. That's also an improvement.
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

Sounds good, i should be able to get all the parts ordered this week.

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