Quick sanity check NPN Tranistors

**kingofkya** · 04-02-2012, 10:55 PM

VU.png

Alright not sure if I got this right in my head its been a while. I would like to use NPN transistors allow a greater current to be used, is my thinking right on the schematic Base to LM3915, Collector to negative Load, Emitter to GND.

Something is nagging in the back of my head but it doesn't seam to want to come foreword.

Thanks Anyone.

PS: Here is Data sheet for Chip
http://www.ti.com/lit/ds/symlink/lm3915.pdf

**David_AVD** · 04-02-2012, 11:09 PM

No, that won't work as the LM391x series have open collector outputs.

There would be many examples on the 'net about how to add output drivers. Here's one that uses PNP output transistors:

http://electronics.stackexchange.com...d-i-hook-it-up

**kingofkya** · 04-07-2012, 10:20 PM

Attempt Number2.

After reading data sheets and that link, (Thanks btw.) I think I get it now does this look right?

Also don't i need pull down resistors Near the base of the transistor?

**David_AVD** · 04-08-2012, 12:57 AM

The 1K resistors are pull-ups. It's hard to read on your diagram, but the resistors from transistor base to LM3915 should be 4.7K or thereabouts.

**kingofkya** · 04-08-2012, 02:08 AM

OH... now that makes sense. Thanks

**kingofkya** · 05-06-2012, 05:29 PM

Attachment 13881

Well I though i should post the result thanks.

Now i just must, figure out why kicad did not export a solder mask.(probably something stupid)

**n1ist** · 05-06-2012, 08:03 PM

Did you have the mask_front and mask_back selected in the plot window? Also, did you send the .gbs and .gts files to the board house?
/mike

**kingofkya** · 05-08-2012, 11:53 PM

Yep that it Why is that off by default...

Some what related, though it was funny.
http://www.adafruit.com/products/557

**kingofkya** · 06-13-2012, 09:17 PM

I was going to post to post a update a while ago, anyways.

2012-06-13_18-05-13_734.jpg
I made quite a few mistakes, but it all worked out thanks to the trusty spare parts drawer.

First I forgot the PNP tranistors in my order. but i had some normal ones the work fine. but the pinouts were different but i got around that.

Second check the layout of the jack, then check the layout, then check the layout. The audio jack did not line up. Drilled a couple holes and fixed again.

Third i forgot to filter the audio so a get a average. So i added a diode, a couple of resistors and a cap. Then I had a working design.

Last sit and watch blinking led for hours.