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Topic: How to control 6 digits 12v led strip seven segments using multiplexing? (Read 672 times) previous topic - next topic

TendoH

I recently wanted to make a large 6-digit digital clock using 12v led strips, I have made the seven segment and type a common anode. but how do I control it? Arduino can only provide a 5v voltage but the LED strip needs a voltage of 12v. I have searched Google and can be solved with external power using NPN type transistors. but when I test it it looks the same for all, for examples 111111 222222 etc. and it's not multiplexed, so how do I handle it? Thanks Before!

And is there an IC that can control the seven seven segment digits without transistors or something?

sorry for bad English, I'm using google translator :)

Grumpy_Mike

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but when I test it it looks the same for all, for examples 111111 222222 etc. and it's not multiplexed, so how do I handle it?
You have to switch the 12V to each digits worth of LED strips one at a time. Then you put the digit you want on the strip outputs. Then change the strip you are powering with 12V and put a new lot of digit levels on the strips. Keep repeating this forever.

To switch 12V from an Arduino you need a PNP transistor or p-channel FET, and switch that with an NPN transistor driven from 5V.

You need to post both your schematic, (NOT a Fritzing pile of crap) and your code for more specific help.

PaulRB

It would be easier to not multiplex the display. Simply use 6 X tpic6b595 chips, one for each digit. Only 3 Arduino pins and no transistors will be needed.

Paul__B

And is there an IC that can control the seven seven segment digits without transistors or something?
I think you mean six seven segment digits - a bit of a tongue-twister there.

As PaulRB says, you need six TPIC6B595 ICs, one per digit.  Sparkfun sells them as modules, but there may be others and the chips themselves are plentiful on eBay.

TendoH

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To switch 12V from an Arduino you need a PNP transistor or p-channel FET, and switch that with an NPN transistor driven from 5V
How to switch PNP Transistor to Switch NPN Transistor? And how much PNP Transistors Are needed? i recently have connected all segments pins to another digits (like seg A to another Seg A on diffirent Digits)

PaulRB

How to switch PNP Transistor to Switch NPN Transistor? And how much PNP Transistors Are needed? i recently have connected all segments pins to another digits (like seg A to another Seg A on diffirent Digits)
You would use the npn to switch the pnp, not the other way around. You would need one pair of npn+pnp for each digit. This is in addition to the npn you have for each segment.


In this diagram, Q1 is the pnp and Q2 is the npn. "Load" is your digit. R3 can be 10K. R2 will depend on the model of pnp you choose and the current required by the digit.

TendoH

You would use the npn to switch the pnp, not the other way around. You would need one pair of npn+pnp for each digit. This is in addition to the npn you have for each segment.


In this diagram, Q1 is the pnp and Q2 is the npn. "Load" is your digit. R3 can be 10K. R2 will depend on the model of pnp you choose and the current required by the digit.
so I need 7 NPN transistors for each segment and NPN + PNP for each digit? and what happens if I don't use resistors? sorry if I ask too many questions

PaulRB

No, you need one npn transistor per segment, 7 in total. Plus one npn+pnp pair per digit. With no resistors, the circuit will not work and the components, including the Arduino will be damaged.

TendoH

No, you need one npn transistor per segment, 7 in total. Plus one npn+pnp pair per digit. With no resistors, the circuit will not work and the components, including the Arduino will be damaged.
ok, so i will use 2N2222 NPN transistors and 2N3906 or maybe BC327 PNP Transistors. can those three transistors can be used?

PaulRB

The npn transistors will be ok. Impossible to say if those pnp transistors will be suitable without knowing how much current needs to be switched. This depends on how much current your segments draw. The pnp will need to switch 7 times more current than the npn.

Wawa

Stop fiddling with (84) transistors, and do as you have been advised in post#2.
High-voltage TPIC6B595 shift register chips are $0.50 on ebay.

Not multiplexing (shift registers) is also a brighter display, and you can PWM/dim with the enable pins.
Only three (or four) Arduino pins needed for the six (or more) displays.
Leo..

PaulRB

Stop fiddling with (84) transistors
Obviously I agree with you, but it's not really 84 transistors, is it? It's 16: 12 npn + 4 pnp. If the OP wants to learn about transistors, why not? Let them get it out of their system and learn something in the process. In the future, when they are using tpic6b595 or whatever, like the rest of us, at least they will have an appreciation of the difficulty of the alternatives. ;)

Wawa


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