connection of 4 7 segment with colon

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Hello I have this set of 7 segment (picture attached) previously I had a similar segment but the only difference was that this one has a colon between the 2nd and 3rd digit ... 

The first problem is that the Decimals in this segment set doesn't work (which actually i am fine with because i dont need them)

but the main problem is that the colons (which I was expecting to be turned on when I applied VCC on D2 and D3 and Ground on DP pin) are turning on in reverse order that is

when I connect VCC to DP pin and ground to D2 the upper led of colon turns on and when I connect VCC to DP and ground to D3 the bottom colon turns on 

my intention is to toggle colon with 1Hz frequency ... But i dont understand How can I do it while bieng able to multiplex the segment at the same time

I have attached my current schematic .... Any help will be appreciated. Thanks

 

edit: in my schematic Blink corresponds to DP pin 

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Last Edited: Sat. Aug 3, 2019 - 04:42 AM
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How would we know? You haven't told us the part number of the display.

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There is no part number on the display :S 

i bought it from a local shop they usually get their other stuff from china 

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I was wondering if you can please have a look at my schematic .... what if I place a PULL DOWN on transistor of D2 and D3 and then instead of multiplexing 4 cases  I would have to multiplex 5 cases ... will something like this work?  

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SufyanRaza26 wrote:

There is no part number on the display :S 

i bought it from a local shop they usually get their other stuff from china 

What about a datasheet? How can you possibly control a complex piece of electronics otherwise if you don't have instructions that explain how to operate it ?

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I DID look at your schematic - how else could I figure out that there was no part number? You're asking us to guess - there could be a zillion displays that look much the same but are internally different. Get your multimeter and use it to sketch out a schematic of the display. Once you can show us the schematic for the display, then we can give better advice. 

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I am sorry I did nt convey my problem correctly ... I did use a multimeter because I failed to find any data sheet which showed me the correct schematic of its circuitry 

I have drawn a sketch of 2nd segment the colon and the 3rd segment in my sketch in this order 

Please tell me if it's not clear enough I 'll try to draw it more clearly 

 

my actual problem is the reverse polarity of Colon LED 

Thanks 

 

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SufyanRaza26 wrote:

my actual problem is the reverse polarity of Colon LED 

That's not how you've drawn it. 

 

 

Both colon LEDs are the same polarity, with a common segment drive (dp), but different digit drive (d2 vs d3).  Just treat them like DP of different digits, since that's how they're wired.  That will fit right into any standard multiplexing setup.

 

What you have labelled as BLINK on your schematic is really just DP.

"Experience is what enables you to recognise a mistake the second time you make it."

"Good judgement comes from experience.  Experience comes from bad judgement."

"Wisdom is always wont to arrive late, and to be a little approximate on first possession."

"When you hear hoofbeats, think horses, not unicorns."

"Fast.  Cheap.  Good.  Pick two."

"We see a lot of arses on handlebars around here." - [J Ekdahl]

 

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I meant reverse polarity as compared to the other 14 LEDs .... in case of Colon LED i have to supply ground to D2 and D3 and in case of other LEDs I am supply HIGH signal to D2 and D3 ... 

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SufyanRaza26 wrote:

I meant reverse polarity as compared to the other 14 LEDs .... in case of Colon LED i have to supply ground to D2 and D3 and in case of other LEDs I am supply HIGH signal to D2 and D3 ... 

 

Then you have answered your own question.

If you know what drive you need, you need to arrange to deliver that. 

Maybe that is why the displays are cheap ex China ? - or maybe they really wanted to save a pin, vs the more usual 7 Segs + DP drive scheme.

You could drive D2, D3 as push pull CMOS, and then float/driveHi the decimal points as needed to ' to toggle colon with 1Hz frequency '

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I did a bit of a Google to see if I could find these displays. What I did find are ones that look the same, but according to their datasheets they're either CA or CC. No reversal on the colon leds. So these ones look they might be a bit 'special'. I can't help but thinking it might be easier to get 'normal' displays rather than do a work around for your 'special' ones.

 

Also, according to the schematic, AVCC is not connected. The datasheet says its important that it is connected to VCC.

Last Edited: Fri. Aug 2, 2019 - 09:02 AM
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Who-me wrote:
You could drive D2, D3 as push pull CMOS, and then float/driveHi

 

Thanks this is what I was looking for but It will not be worth it to change the schematic completely it would be easier if I buy some other segment as Kartman suggested

 

 

 

Thank you!

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Is there an issue with a simple inverting transistor driving those two lines?

 

Neil

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I wouldn't connect anything to my colon. Not after last time...

Four legs good, two legs bad, three legs stable.

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umm sorry but i dont understand what do you mean by inverting transistor ??are u referring to implementing a NOT logic on those lines? 

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what happened last time ? :S 

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Indeed, just an inverter on those lines. I suggested a transistor because the same component can both invert and provide a current source.

 

But you'd also need to change your multiplexing schema to pull d2 and d3 low instead of high when you need to drive the colons. I like the idea of 'buy some new 7-seg displays'...

 

Neil