Cascading LM3914 Bar/Dot displays

[Wannabe EE]

Here is my Article and Projects for Cascading 2 or 3 LM3914's.
It includes the PCB's for them.

Thank you Gary (I am assuming you are Gary, audioguru seems to know you ). I had already seen it and studied it. I am about to post a thorough explanation (in the next hour) of what I have learned. No one has answered my questions directly, so I spent many hours studying various resources online. I now have a better understanding and will post so that others will have it in one place.

-EDIT-

I have now posted the explanation here:

https://www.electro-tech-online.com...r-dot-displays-a-complete-explanation.126056/

 

[aardyvarky]

Dear all on this subject - thank you for a most entertaining read, and I am sure you eventually achieved your goals, but all the links are broken and therefore I can get no farther on my quest to drive 40 LEDs using 4 LM3914's in dot mode. It works in bar mode (although with modern LEDs the brightness changes as the scale increases...). I have the age-old problem of LEDs staying on when they shouldn't, have connected pin 9's as per the datasheet, and added the 20k resistors where I should, all to no avail. I am thinking that the LM3914 is not all it's cracked up to be, and to do it with opamps and gates (it's ONLY another 16 IC's!). I have tried running all 4 LM3914's with and without using their internal voltage sources. Please redo the links before I shelve my LM3914's for ever!

 

[alec_t]

The problem may be due to the fact that the LM3914 has a deliberate small overlap between the voltages where one LED turns off and the adjacent LED turns on. What voltage range are you using for the signal input? If that range, divided by 40, is less than the overlap then you must expect more thn one LED to be on at a time.

 

[JimB]

all the links are broken

Please redo the links before I shelve my LM3914's for ever!

A bit of a problem there!
Many attachments were lost in a server crash a few years ago, and are gone forever.
The originator of this thread, Wannabe EE, has not been seen in the forum since 2013, so he is unlikely to be back to re-post the attachments.

JimB

 

[chemelec]

Here is My REVISED LINK.

http://chemelec.com/Projects/Volt-Meter-2/VoltMeter-2.htm

Aardyvarkv, Sounds like you have GROUND LOOPS in your Circuit.
Common Point Grounds are Very Important, when using this IC.

 

[JimB]

Thank you chemelec

JimB

 

[chemelec]

It is Here for awhile, But I plan to completely Shut Down my Website on Oct 16, 2017.

 

[aardyvarky]

Alec_t - You may have a point there - I'll try increasing the supply voltage (currently 5v) to allow a higher Vmax input at full scale, though my test is only using 3 x 3914's over 3.5v so should be 0.111v, but as you say, a bit near the knuckles maybe.
JimB - A shame, but thank you.
Chemelec - Thank you also, but my ground points are as physically close to each other as is possible! Still, could be an issue, which I'll investigate.
In general, my firewall doesn't like any of those links, and (this being Windoze) I'll avoid them for now and persevere (good job there's no deadline for this project!).
The odd thing (to me anyway) is that it works perfectly in bar mode, so if all else fails I'll decode that (40 x ExNor gates).
Thanks once again to everyone.
I just have to add this - we went to BC in 2012 and it is stunningly, stunningly beautiful. Sorry for deviating from electronics!

 

[chemelec]

If you just have 2 LED's Lit at the upper most Overlap of two LM3914s, that is somewhat Normal.
But if you have Others Elsewhere, it sound like Ground loops.
Each LM39i4 Requires a Common Point Ground "at and for" Each IC.
Look at My PCB Layouts to get the Idea.

aardyvarky, Where do you live?
Yes BC is Beautiful.

My Site Closing is Mainly because of Declining Interest of People actually Building projects these days.
Just buying the China, Ready Made stuff.
Really a shame and I have over $100,000 in parts to Throw away. Plus Equipment.

 

[aardyvarky]

Chemelec - in that case I'll abandon dot mode and decode bar mode. I live in mid-west Wales, which has its own beauty, if somewhat smaller in scale! Many thanks. And yes, such a shame.