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Topic: Single digit, Seven segment Numitron program and pcb design needed. (Read 14476 times) previous topic - next topic

Daddyfredregill

I dont want the super cap to actuall light up the display it is for when the lipo battery goes dead. Just to back up thr time on the rtc till i can get to a chatger.

Daddyfredregill

Also what do you need to switch from lipo power to charging power when you plug and unplug the unite?

wvmarle

Not sure how to go with that. Needs some research. Such a battery adds a lot to the bulk of the whole thing, and you're running at about 3.5V (fully charged they may go over 4V but not for long). That'd be too low to properly light your display.
I just checked the video you linked to again, and it was quite noticeable how the brightness of the display went up the moment they connected the device to the USB power. All demo on the video was also on USB power rather than the battery.
A 3V button cell would be a cheaper/smaller solution for your RTC than a supercap, and it should be able to provide backup power for a few years.
For the PCB layout my idea is to place all the components on the back, partly in between the pins of the display.
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Daddyfredregill

I guess i never thought of battery voltage level unplugged. I was thinking 5v usb the whole time. How do you boost/keep the voltage up aroind 5v for the display? Maybe it cant be done?

wvmarle

You'd have to use a boost converter. The modules that I have used are 17x27 mm in size, and don't go much smaller. What I heard on the forum a few times before is that those things are tricky to design so better just use a ready-made module. The easiest would be to run the whole system on 5V, so have the battery boosted for both the controller and the display.

A quick search turned up this module which seems to fit the bill perfectly:
https://item.taobao.com/item.htm?spm=a230r.1.14.65.7cecf835rEFb7P&id=555405101531&ns=1&abbucket=8#detail

Small, can still do about 100 mA at a near-empty battery, enough for your clock.
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Daddyfredregill

Very nice, thanks for all the info you have given me i really appreciate it. But now i am at a loss. I have no idea where to start? I really don't know how to design circuits.

wvmarle

Actually for the fun of it I started on that already :-) Mostly out of curiousity. That's how I got to the PCB sizes.

Schematic:

This supercap is recharged the moment the battery is connected, to about 4.4V. The diode is there to stop backflow, the charge of the supercap must be reserved for the RTC only. The 50 mF should last about 40 hours with this RTC - the RTC chosen mostly as these seem to be rather popular in the Arduino world. The smaller the supercap value the smaller the part size but the shorter the time the RTC keeps it's time.

The image of your numitron is not clear enough, some numbers are unreadable.
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

Very nice, thanks. If i remember the 1,16,9,8 are not used. I did not use them to get the diplay to make a number 8. Number 5 is on the left side in the middle it is a common. I could not get the decimal #9 to work, so i am not using that one.

Daddyfredregill

I noticed in the hackaday.io build I linked he has all all the files needed to build his clock. It seems to have quite a few more components involved. I wonder if you could reverse engineer his a little bit and make it work with my display? Here is the link for the github files.


https://github.com/WeisTekEng/MicroNumitron/tree/master/Trunk/Hardware


wvmarle

Code: [Select]
For the display, I have these connections:

[TT]
1  ?
2  C.A.
3  f
4  g
5  ?
6  e
7  d
8  ?
9  ?
10 C.A.
11 c
12 C.A.
13 C.A.
14 b
15 a
16 ?


And two remain unconnected: D.P. and one more C.A. The numbers marked with them are too unreadable. That would leave three unconnected pins.

I just downloaded the schematic, indeed more components:
- many more decoupling caps (I should add one for the RTC). They have more ICs so more such caps.
- Buttons are wired with external pull-down, instead of using the internal pull-up.
- I didn't add a reset button. Not necessary; you can power cycle it instead. Reset is only good for development time. So just adding a pull-up resistor for RESET.
- External crystal for the processor - not needed unless running at 16 MHz and that's not necessary for this application. Internal 8 MHz is good enough.
- external controller for the numitron, don't see the need, plenty of I/O and the power to sink is 8 mA only. No problem for an ATtiny pin.
- Temperature sensor.
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Daddyfredregill

Ok that makes sense, so as far as the display you said you could not see some of the numbers. I might have found a better pdf. I will post it so you can see it.

Daddyfredregill

Pin 5 is a common anode- it has to be hooked up with all the other CA

Pin 9 is the Decimal- I could not get it to work but that is ok. I am not using it.

Pins 1,8,16?- I don't have them hooked up and dont seem to do anything.

Hope that clears it up

wvmarle

Much more readable indeed :)

According to the data sheet those three pins are indeed not connected.
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 at this point with your schematic. I just need to figure out how to implement the usb/battery auto switching circuit. Correct? I think this is the circuit.

wvmarle

It makes more sense to not have the battery charger circuit on board, to save space. Just a connector for the batteries, and the SPI programming headers (in the form of six plated holes).

PCB size can be as small as 0.45x1.8 inches, including space for a for time backup and battery connection. Those are bulky. That size is a little longer than two of your displays end to end.
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.

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