Problem to Use MAX6955 with 16 7-Segment with four (4) led per segment
Archiver
Posts: 46,084
Request/Problem:
i am trying to use this chip with Bs2p40 of PARALLAX, I don't have problem
to comunicate and configurate this chip by I2C, But I have a problem with
Display... Because, I am trying to use this chip with sixteen (16)
7-segment and each of segment is construcction by me by four (4) led
(Vd=0,8Vdc)... When a put in the MAX6955 this display.. I don't see
anywere, but If i put only two (2) led per segment I can see the
numbers..... I don't understand this because I can see in your datasheet
that if possible to put segment od (Vd max =V+ - 0,8)... Can you help me
about this requierement, I need to put this plataform in funtion with four
(4) led per segment...
I appreciate your prompt response
Best Regards
Eng. Damian Trujillo G.
Venezuela, Caracas
i am trying to use this chip with Bs2p40 of PARALLAX, I don't have problem
to comunicate and configurate this chip by I2C, But I have a problem with
Display... Because, I am trying to use this chip with sixteen (16)
7-segment and each of segment is construcction by me by four (4) led
(Vd=0,8Vdc)... When a put in the MAX6955 this display.. I don't see
anywere, but If i put only two (2) led per segment I can see the
numbers..... I don't understand this because I can see in your datasheet
that if possible to put segment od (Vd max =V+ - 0,8)... Can you help me
about this requierement, I need to put this plataform in funtion with four
(4) led per segment...
I appreciate your prompt response
Best Regards
Eng. Damian Trujillo G.
Venezuela, Caracas
Comments
I'm guessing that you are using a 5 Volt power supply to drive the LEDs. If
that's the case then when you connect 4 LEDs in series the forward voltage
drop could be from 6.4 Volts for red to 16 Volts for Blue LEDs.
If it works with 2 LEDs then the forward drop is <5.0 V, like with two Red LEDs.
You're going to have problems with the MAX 6955 because it's only rated for 5.5
V and with 16 digits of display you will be limited to 935 mA/(16*7) =
8 ma per segment.
It was this type of problem (and a different set of problems with multiplexed
digits) that led me to the Allegro 6276 static LED driver. It's rated for
17 Volts and 1.475 Amps. It has 16 drive pins so can support two 7 segment
digits plus a decimal point.
My first prototype PCB is for 0.56" CA 7 segment LEDs, but same circuit would
work for 6 digits of your display. This prototype is designed to daisy
chain so can be used for 6, 12, 18, 24, 30, etc. digits assuming you have a
power supply that can handle the current.
See: http://www.pacificsites.com/~brooke/PClock.shtml
Have Fun,
Brooke Clarke, N6GCE
http://www.precisionclock.com
http://www.prc68.com
>
> Date: Sat, 22 Feb 2003 17:02:33 -0400
> From: "dtrujillo_riese@c..." <dtrujillo_riese@c...>
> Subject: Problem to Use MAX6955 with 16 7-Segment with four (4) led per
segment
>
> Request/Problem:
>
> i am trying to use this chip with Bs2p40 of PARALLAX, I don't have problem
> to comunicate and configurate this chip by I2C, But I have a problem with
> Display... Because, I am trying to use this chip with sixteen (16)
> 7-segment and each of segment is construcction by me by four (4) led
> (Vd=0,8Vdc)... When a put in the MAX6955 this display.. I don't see
> anywere, but If i put only two (2) led per segment I can see the
> numbers..... I don't understand this because I can see in your datasheet
> that if possible to put segment od (Vd max =V+ - 0,8)... Can you help me
> about this requierement, I need to put this plataform in funtion with four
> (4) led per segment...
>
> I appreciate your prompt response
>
> Best Regards
>
> Eng. Damian Trujillo G.
> Venezuela, Caracas
I appreciate your help... You give me the solution..., but i have a one
question more for you..
If i have to put sixteen (16) 7-segment.. I must game to enable chip (6276)
to put eight (8) chip in the same interface serial....
Do you know other chip with same characteristic... (Power Led) with more
number of 7-segment?
I apreciate your help and email
Best Regards
Eng. Damian Trujillo G.
Venezuela, Caracas
Mensaje Original
De: Brooke Clarke [noparse]/noparse][url=http://forums.parallaxinc.com/group/basicstamps/post?postID=S-2bpbpHmqzq5CctjHivqfbvQWqLjELgtTbtjwL3kPByNbCbVtITyeYK1WMMXmuRgRribWAQmUe2tMs7]brooke@p...[/url
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Asunto: [noparse][[/noparse]basicstamps] Problem to Use MAX6955 with 16 7-Segment with four
(4) led per segment
Fecha: 22/02/2003 22:28:04
Mensaje:
Hello Damian:
I'm guessing that you are using a 5 Volt power supply to drive the LEDs.
If that's the case then when you connect 4 LEDs in series the forward
voltage
drop could be from 6.4 Volts for red to 16 Volts for Blue LEDs.
If it works with 2 LEDs then the forward drop is <5.0 V, like with two Red
LEDs.
You're going to have problems with the MAX 6955 because it's only rated for
5.5 V and with 16 digits of display you will be limited to 935 mA/(16*7) =
8 ma per segment.
It was this type of problem (and a different set of problems with
multiplexed digits) that led me to the Allegro 6276 static LED driver.
It's rated for
17 Volts and 1.475 Amps. It has 16 drive pins so can support two 7 segment
digits plus a decimal point.
My first prototype PCB is for 0.56" CA 7 segment LEDs, but same circuit
would work for 6 digits of your display. This prototype is designed to
daisy
chain so can be used for 6, 12, 18, 24, 30, etc. digits assuming you have a
power supply that can handle the current.
See: http://www.pacificsites.com/~brooke/PClock.shtml
Have Fun,
Brooke Clarke, N6GCE
http://www.precisionclock.com
http://www.prc68.com
>
> Date: Sat, 22 Feb 2003 17:02:33 -0400
> From: "dtrujillo_riese@c..." <dtrujillo_riese@c...>
> Subject: Problem to Use MAX6955 with 16 7-Segment with four (4) led per
segment
>
> Request/Problem:
>
> i am trying to use this chip with Bs2p40 of PARALLAX, I don't have problem
> to comunicate and configurate this chip by I2C, But I have a problem with
> Display... Because, I am trying to use this chip with sixteen (16)
> 7-segment and each of segment is construcction by me by four (4) led
> (Vd=0,8Vdc)... When a put in the MAX6955 this display.. I don't see
> anywere, but If i put only two (2) led per segment I can see the
> numbers..... I don't understand this because I can see in your datasheet
> that if possible to put segment od (Vd max =V+ - 0,8)... Can you help me
> about this requierement, I need to put this plataform in funtion with four
> (4) led per segment...
>
> I appreciate your prompt response
>
> Best Regards
>
> Eng. Damian Trujillo G.
> Venezuela, Caracas
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No, the Allegro 6276 is the only chip I've found that can easily handle large
LED displays. It costs way less than the 6955.
Also I have been using it with the Latch Enable tied permanently to +5 so only
Data, Clock and Output enable need to be controlled
in the serial interface.
This works using a PIC but you may get "blinking" if you use a BS, so may need
to use the Latch Enable line.
Have Fun,
Brooke Clarke
PS I have posted a photo of the trace side of prototype "LED1" PCB at:
http://www.pacificsites.com/~brooke/PClock.shtml
> Date: Sun, 23 Feb 2003 14:55:40 -0400
> From: "dtrujillo_riese@c..." <dtrujillo_riese@c...>
> Subject: Re: Problem to Use MAX6955 with 16 7-Segment with four (4) led per
segment
>
> Thank Brooke Clarke,
>
> I appreciate your help... You give me the solution..., but i have a one
> question more for you..
>
> If i have to put sixteen (16) 7-segment.. I must game to enable chip (6276)
> to put eight (8) chip in the same interface serial....
>
> Do you know other chip with same characteristic... (Power Led) with more
> number of 7-segment?
>
> I apreciate your help and email
>
> Best Regards
>
> Eng. Damian Trujillo G.
> Venezuela, Caracas