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Topic: Problem with TIP120 (yes another one) (Read 494 times) previous topic - next topic

VicenteChazard

Hi guys!

I'm trying to drive a 7 segment giant digit that works at 12v with an Arduino and some TIP120.
My idea is for the arduino to control each TIP120 to turn on/off each segment.

The digit as a common anode (negative pin) for all 7 segment, so each TIP120 will have to drive the +12v (positive).
I have a small power supply that convert 12v to 5v and 3.3v, that will power both the Arduino(5v) and the Digit(12v).

I have tested each segment, connected to the emitter of a TIP120, the colletor to 12v, and the base to 5v... it works fine.
But wen I plug the base to an arduino pin (set to HIGH) nothing happens...

I know the pin works since it turns on a simple LED + resistor...

Can anyone help?

larryd

Show us a good schematic of your circuit.
Show us a good image of your wiring. 
Give links to components.
Posting images: 
https://forum.arduino.cc/index.php?topic=519037.0



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If you are asked a question, please respond with an answer.
If you are asked for more information, please supply it.
If you need clarification, ask for help.

VicenteChazard

Here is the circuit schematic:


The code is the simple "Blink" with the proper pin Output.
For the image purposes it would be the pin D2.

Components:
- TIP120
- Arduino UNO
- Power Supply
- 7 Segment Digit

larryd

#3
Jul 30, 2019, 12:20 am Last Edit: Jul 30, 2019, 12:41 am by larryd
The LED segments should have series dropping resistors.




You need a transistor base resistor.

The power supply will be quite limited in the current it can supply as there is no heatsinking.

EDIT

If you have the 102AX, it is common cathode.
Appears you have GND going to the display common and +12 to the transistor collector.



Looks like you are trying a cct. similar to above i.e. Q1 where Q2 would would apply.

However you would then need a level shifting transistor to switch +12v with a common cathode display.

What is suppling the 12v?

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Wawa

Large digits are usually driven with a single TPIC6B595 chip (or family member).
They can be daisy-chained for e.g. a whole score board.
And that would only use three Arduino pins.
Read this.
Leo..

VicenteChazard

#5
Jul 30, 2019, 02:42 pm Last Edit: Jul 30, 2019, 10:24 pm by VicenteChazard
Hi again!

EDIT

Quote
What is suppling the 12v?
A 12v 2A power supply, connected to a Multi Output Voltage Conversion (3.3V, 5V & 12V)

Quote
Looks like you are trying a cct. similar to above i.e. Q1 where Q2 would would apply.
I have tested the Q2 cct, and it still does not work.


Quote
If you have the 102AX, it is common cathode.
To be honest I'm always mixing cathode and anode. So to make it clear to make any segment work, I have to single pin that I connect to GND and every other pin has to be connected to +12V (each pin for each segment)

Quote
Large digits are usually driven with a single TPIC6B595 chip (or family member).
They can be daisy-chained for e.g. a whole score board.
And that would only use three Arduino pins.
I have just checked the TPIC6B595, they appear to be a good solution for my problem, but before I order any, I need to be sure that they can drive my digit (only 1 negative pin)

Some other concerns:

- I have a bunch of TIP120, and I would prefer to use them, so I wont need to spend more money and time waiting for the new chip.

- As I said in my first post, I have tested each segment directly to the 12v and they work fine.
I have also tested each segment, with a TIP120 (collector:12v, emmiter:segment(+), base:+5v) and i also works fine. But wen I plug the base to an arduino pin (set to HIGH) nothing happens.

Wawa

I have just checked the TPIC6B595, they appear to be a good solution for my problem, but before I order any, I need to be sure that they can drive my digit (only 1 negative pin)
A TPIC6B595 can only be used with a common anode 7-segment display.
The 12volt is connected to the common anode, and the seven cathodes are connected to the outputs of the 595, with seven current limiting resistors in between. There is an eight output for the optional DP.
Leo..

larryd

No technical PMs.
If you are asked a question, please respond with an answer.
If you are asked for more information, please supply it.
If you need clarification, ask for help.

MarkT

Here is the circuit schematic:

No, that is a wiring diagram, not a schematic.  Schematic uses standard symbols for everything and is about the way the thing works, not the details of building a copy of the circuit.

You are trying to use the TIP120 as an emitter follower - however you cannot get any voltage gain that
way, so it cannot level-shift upto 12V, the LED display will see perhaps 3.5V at most, due to the base-emitter drops from 5V at the base of the TIP120.  Thus the display does nothing.

If using an emitter follower for switching you will waste a lot of power in the transistor, its not efficient -
common-emitter circuit is the one to use, and for high-side switching you need to level to shift to 12V first,
then use a PNP transistor in common-emitter configuration to actually switch the load.  Typically that means
needing two transistors.
[ I will NOT respond to personal messages, I WILL delete them, use the forum please ]

VicenteChazard

Hi again!

Quote
Do you have:
102AX
or
102BX
I honestly don't know.
The only inscription on the display is: FJS30101AH.
I have checked my order detail and it says: Cathode 30101AS.


MarkT, thanks for your explanation(s).

I have no problem abandon the TIP120, but I need an alternative transistor, MOSFET, level shifter... whatever works.
I have been searching the web for possible solutions, could a Transistor BC337 work?

MarkT

With common cathode you require PNP or p-MOSFETs to switch the 12V high-side, and a small-signal NPN transistor as a level shifter.  The BC337 could be an NPN level shifter.

See post #4 in this thread: https://forum.arduino.cc/index.php?topic=555862.0
[ I will NOT respond to personal messages, I WILL delete them, use the forum please ]

Wawa

AS = common cathode.
If you want to make things easier then throw them in the bin and order new common anode displays.
Order some $0.50 TPIC6B595 chips with it as well.
Leo..

VicenteChazard

#12
Aug 01, 2019, 02:22 pm Last Edit: Aug 01, 2019, 02:23 pm by VicenteChazard
Quote
If you want to make things easier then throw them in the bin and order new common anode displays.
At the moment this not an option, I will have to use them.

Quote
With common cathode you require PNP or p-MOSFETs to switch the 12V high-side, and a small-signal NPN transistor as a level shifter.  The BC337 could be an NPN level shifter.

See post #4 in this thread: https://forum.arduino.cc/index.php?topic=555862.0
I have checked the link, the end result is kinda funny, but there is a circuit proposal that I think should work for me:

I would only have to addapt the gate voltage from 3.3v to 5v, therefor, R4, R5 and Q3... correct?

VicenteChazard

Hi again!

Since I hadn't time to go get the new parts yet, I decided to try to build the circuit in TinkerCAD.
Since there is no 12v 7 segment available in TinkerCAD, I used a 12v motor.

Apparently the circuit works, but the motor gets a constant 12v, although the RPM varies.
So now I wounder if it will actually work with the 7 segment display.

VicenteChazard

Ok, I finally got all the pieces and built the circuit... anf for some reason it doesn't work.

I checked, double checked, triple checked.
I exchange all the components for new ones... the result is always the same:

The 7 segment display lights up instantly without adding the 3.3v.
And wen I do add the 3.3v nothing happens.

Any advise on how to trouble shoot this?

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