Multiplexed signals to drive large 7 segment leds

[djv2008]

Hey Eric and Mike,
Just out of curiousity, who is your favorite Premier League team? There arent a lot of real football fans around here in the states to talk about the Premier League with. I was also wondering, are stadiums like Old Trafford always sold out? It seems that way. Over here they have a hard time filling a stadium with 40,000 to watch American Football.

 

[ericgibbs]

A sketch would be great. I really appreciate both your patience with my noobie status. I must admit this is the best forum I've seen in a long time!

hi djv,
I'll post a diagram over the weekend.

Cant help with the football question.

 

[ericgibbs]

A sketch would be great. I really appreciate both your patience with my noobie status. I must admit this is the best forum I've seen in a long time!

hi djv,
I'll post a diagram over the weekend.

Cant help with the football question.

 

[djvsmarkviii]

Thanks Eric!

 

[ericgibbs]

Thanks Eric!

hi,
Have a look at this.**broken link removed**

EDIT:
moved wire up one.!

 

[djvsmarkviii]

That looks great Eric. Let me see if I understand the drawing. The multiplexed signal is also going to the 7407 chip which buffers the signal for each segment for the large display. From what I saw on the data sheets for a 7407 chip it can sink 40ma. I will have 8 5mm leds (2 pairs of 4in series) to make up each segment. If all segments on a paticular data line are active it would draw under 800ma. I dont think the 7404 can handle that. Is there something I should put in between the outputs of each dataline from the 7404before the large displays to handle the current?

 

[Boncuk]

Here is my way of driving large 7-segment LEDs. The MosFets are a bit overkill, but work well for any size display.

LED current is 700mA.

Boncuk

 

[ericgibbs]

That looks great Eric. Let me see if I understand the drawing. The multiplexed signal is also going to the 7407 chip which buffers the signal for each segment for the large display. From what I saw on the data sheets for a 7407 chip it can sink 40ma. I will have 8 5mm leds (2 pairs of 4in series) to make up each segment. If all segments on a paticular data line are active it would draw under 800ma. I dont think the 7404 can handle that. Is there something I should put in between the outputs of each dataline from the 7404before the large displays to handle the current?

hi djv,
This is the first time you have given the LED's as being 'high power' I was under the impression they where going to 'ultra bright', about 30mA.!

BTW: there is an important difference between 7407 and 74LS07 devices.

To cope with the 800mA load I would suggest N MOSFET's on the segment outputs and either P MOSFET's or pnp Darlington transistors on the digit drivers of the 74LS06's NB: this is now an inverting buffer.

the following mods are for:
Boncuk drawing as starting point.

A 74LS04 should be used between the ULN inputs and the PIC, this is to give a double inversion of the seg driver signal.

IIUC the digit drivers will also need inversion before the BS170's

 

[djv2008]

Hi Eric,
Sorry about the confusion on the segment displays. Here is what I found for the array per segment. The counter display will have 4 x 7 segment displays showing(min:secs). The 10" displays will be homemade with each segment consisting of 8 leds. The specs for the indvidual leds is 20ma forward current & Vf of 1.5v. I used a led wizard program and it showed that each segment array would use 40ma. There is an attached pic from led wizard. So if all 4 segments of each display are on it would use 160ma, not 800ma like I originally thought. My bad. So since that is the case, would the last drawing from Boncuk be ok as is or does it still need modification? Thank for baring with me.

 

[ericgibbs]

Hi Eric,
Sorry about the confusion on the segment displays. Here is what I found for the array per segment. The counter display will have 4 x 7 segment displays showing(min:secs). The 10" displays will be homemade with each segment consisting of 8 leds. The specs for the indvidual leds is 20ma forward current & Vf of 1.5v. I used a led wizard program and it showed that each segment array would use 40ma. There is an attached pic from led wizard. So if all 4 segments of each display are on it would use 160ma, not 800ma like I originally thought. My bad. So since that is the case, would the last drawing from Bancuk be ok as is or does it still need modification? Thank for baring with me.

hi,
The current of 200mAish is more realistic. Are you sure about the 1.5V forward drop.?

Do you need another circuit.?

 

[djv2008]

Hi Eric,
I bought the leds from JAMECO part# LUR3833 and thats what it listed. I thought as you that foward voltages should be about 2.1 volts. Using that voltage it would be around 40ma. Is that correct? Any ciruit ideas are greatly appreciated and very welcome!

 

[djv2008]

I found this schematic for led displays. It shows a common cathode type disply. I need it for a common anode. Can I modify this for CA segments?

 

[ericgibbs]

I found this schematic for led displays. It shows a common cathode type disply. I need it for a common anode. Can I modify this for CA segments?

hi,
The voltage levels and sense are not suitable for your application.

 

[ericgibbs]

I found this schematic for led displays. It shows a common cathode type disply. I need it for a common anode. Can I modify this for CA segments?

hi,
I will modify one of my earlier clock circuits and post it tomorrow.

 

[ericgibbs]

hi djv.

Have a look over this.
It was a 6 digit clock, chopped to 4 digit. OK.?

If you can get a HEF40098 i/c, the two 74LS04 could be replaced by one ic.

 

[djvsmarkviii]

That looks pretty awesome.
I have plenty of 74ls04 chips so that will work.
My question is the ZTZ751 PNP transistor the same as a Farichild MPS751?
The specs are here https://www.electro-tech-online.com/custompdfs/2009/01/mps751.pdf
I believe it has enough (ummph) to handle the application.

I really want to thank you again for your help.

Another question I have is: will I be able to run the +5v signals for the Digit drivers and the individual segment lines from my hand held remote to the large fixed display that will house the circuitry you have supplied with a cable about 10 foot long? Or do I need to strengthen the signals from the microcontroller in my hand held remote to the large display?

 

[djv2008]

Hi Eric,

That looks awsome.
I have a lot of 74ls04 ic's laying around. I do have a question about the ZTZ751 PNPs. I cant find them anywhere. The closest I could find was a spec sheet on a Fairchild MPS751, but I cant locate that chip anywhere. Is there another PNP transistor I could use?

Sorry about the double post. The one previous to this didn't show up till this morning.
By the way, I'm sure you figured out that both DJVs are me. I use one at home and one at work.

 

[ericgibbs]

Hi Eric,

That looks awsome.
I have a lot of 74ls04 ic's laying around. I do have a question about the ZTZ751 PNPs. I cant find them anywhere. The closest I could find was a spec sheet on a Fairchild MPS751, but I cant locate that chip anywhere. Is there another PNP transistor I could use?

Sorry about the double post. The one previous to this didn't show up till this morning.
By the way, I'm sure you figured out that both DJVs are me. I use one at home and one at work.

hi,
Thats a typo it should read ZTX751. Can you get this.?

The MPS751 collector current is too low.

You require a current of approx 500mA min at a gain of 100.

Corrected the drawing, Iss2

EDIT: what power supply will you be using for this remote display. ?

 

[djv2008]

Eric,
I'm having a hard time finding a cross reference. I did find this
https://www.electro-tech-online.com/custompdfs/2009/01/64731.pdf
The voltages are shown as positive.

Or is this overkill?
https://www.electro-tech-online.com/custompdfs/2009/01/MJE15034-DPDF.pdf

 

[djv2008]

Eric,
I found the ZTX751 at NEWARK supply and I'm ordering them right now.