Continue to Site

Welcome to EDAboard.com

Welcome to our site! EDAboard.com is an international Electronics Discussion Forum focused on EDA software, circuits, schematics, books, theory, papers, asic, pld, 8051, DSP, Network, RF, Analog Design, PCB, Service Manuals... and a whole lot more! To participate you need to register. Registration is free. Click here to register now.

Register Log in

Controlling high power LED displayed with PIC MCU

Status
Not open for further replies.
T

ThePringler

Junior Member level 1
Joined
Sep 16, 2011
Messages
15
Helped
0
Reputation
0
Reaction score
0
Trophy points
1,281
Activity points
1,395
Hi all,

I am building an alarm clock that will be driven by several PICs and displayed on an LED display. One of my displays requires a fair bit of power (15V and way more AMPS then a PIC can handle) The segments become "light" when the SegmentPIN is set to low. I will have all my digits tied to +15v and i will control each segment individually rather than multiplexing (only 4 digits). Heres my question...


Will i kill my PIC by doing this?

When the segment is light, the PIC will see 0 volts
When the segment is off, the PIC will output 5V

zzz.JPG


Thanks for the input!

-B
 

Your PIC will be damage. To connect two different voltage circuits are quiet easy, but that's not as easy as you did. You can add a transistor array ULN2003 or ULN2803 between display and PIC.
 

Arch Zone said:
Your PIC will be damage. To connect two different voltage circuits are quiet easy, but that's not as easy as you did. You can add a transistor array ULN2003 or ULN2803 between display and PIC.
Click to expand...


Thanks for the reply! I will try out a ULN2003 (data sheet below)




How would i use this for application, i have attached a rough schematic, is this correct?

zzz.JPG


Thanks for the help again!
 

Yes, your connection diagram is correct but note that ULN2003 can only output 500mA/ output and if you intend to use any number of output simultaneously then the output current is limited based on duty ratio (even a single output has less than 500mA with 100% duty)

ULN2003_max_current .gif
 

alexan_e said:
Yes, your connection diagram is correct but note that ULN2003 can only output 500mA/ output and if you intend to use any number of output simultaneously then the output current is limited based on duty ratio (even a single output has less than 500mA with 100% duty)

View attachment 68750
Click to expand...

Thanks, that graph is very helpful. This is going to complicate things.... What would you guys suggest to maintain equal brightness? Should i try to multiplex the segments so only one is light at a time?
 

The last time I tries to multiplex a four segment display (a small sized one) at a segment level I got very dim output and I had to use the digit multiplexing.

What kind of display do you have , you mention "15V and way more AMPS then a PIC can handle", how big is it?
 

ThePringler said:
Thanks, that graph is very helpful. This is going to complicate things.... What would you guys suggest to maintain equal brightness? Should i try to multiplex the segments so only one is light at a time?
Click to expand...

I only need 30mA per segment.

---------- Post added at 23:04 ---------- Previous post was at 23:02 ----------
alexan_e said:
The last time I tries to multiplex a four segment display (a small sized one) at a segment level I got very dim output and I had to use the digit multiplexing.

What kind of display do you have , you mention "15V and way more AMPS then a PIC can handle", how big is it?
Click to expand...


Ya im really not wanting to mutliplex as i have seen the same results as you mentioned above. Data sheet below..

7SG23011BB Technical Data

All i need to do is control the "lows" of the segments to light them up. There has got to be an easier way then implementing 4 more IC's.

Thanks for the help here alexan_e
 

ULN2803 has a better current rating and I think would suite your need

ULN2803_output.GIF

With 30mA * 8 segment (including dot) you need 240mA , with 4 display and 100 duty the above driver works fine although the temperature of the driver will probably increase.

Another alternative is ULN2065, ULN2069 for 1.5A


Note that the display DC Forward Current (If): 30 mA is the absolute max and you don't want that high current, the nominal operating current is 20mA
 

alexan_e said:
ULN2803 has a better current rating and I think would suite your need

View attachment 68751

With 30mA * 8 segment (including dot) you need 240mA , with 4 display and 100 duty the above driver works fine although the temperature of the driver will probably increase.

Another alternative is ULN2065, ULN2069 for 1.5A


Note that the display DC Forward Current (If): 30 mA is the absolute max and you don't want that high current, the nominal operating current is 20mA
Click to expand...

Thanks for that.

I have one more question here. Would a "1" be brighter then a "6". 2 segments light vs 6 segments light.

Thanks again!
 

The brightness of "1" and "6" is the same because each segment is driven from each transistor array's pin and the current of each pin will be the same. But, if you use small current power supply, the brightness can be decrease because they will need more power to operate and the power supply can not feed it.
 

Status
Not open for further replies.

Similar threads

Part and Inventory Search

Welcome to EDABoard.com

Sponsor

Back
Top