Hi Everyone,
I am getting some strange results from trying to run a 12 segment led bar (KWLR1230CDUGB) with a TX74HC595 and 3 NPN2222 on the common cathodes.
I have the 595 being controlled by an arduino mini and using a voltmeter I can see all the pins rising to 4.7v in series that matches my sketch.
If I connect either of the cathode pairs directly to ground everything works as expected. As I switch the ground to each cathode pair the led segment is divided into 3 segments of LEDs 4 in each. I can turn on the green, then the red, and then both to make yellow.
When I add in a npn 2222 for a low side switch I get sporadic behavior and it looks like in some cases the expected LEDs light and then the other 2 segments are very dull. The 3 out pins on the arduino all turn on as expected when I set them to high and show 4.7v.
I made this on a bread board and it worked. Tore it down and soldered everything on a PCB and I am having major issues.
Can someone advise on test points to further dissect what is wrong? And can someone confirm this is the correct way to do this?
I am combining pins 1,14 and 9,6 and 7,8 on the led bar. These are going to one of 3 collectors on the npn 2222. The emitters are all connected to ground.
3 outputs from the arduino are connected to a 220kohm resister and then to the base on each transistor.
The 8 lines from the 74HC959 are connected to 8 120k resisters and to the LED Bar anode lines.
Ummm no capacitors on anything. Will take a look at that. I assume that goes between the power rail and the vcc on the 595? And this did work on a bread board just must have messed something up when moving to a board.
Forum software has a "gotcha", it rejects images with certain meta-data embedded. Load the image file in a graphics program like "paint" and then export it from there, add it as an attachment to the post.
But what the heck is a NPN2222? Never seen that part before...
Sorry changed the above. I am using 220ohm resisters on each led in the bar and on the 3 base connectors of the transistors. Will add a cap to the 595. But this was working on a breadboard. I have moved it to a blank pcb and soldered everything up.
I have used a voltmeter and see what I would expect on the 595 and arduino outs. If I skip the transistors and take the bar right to ground it works. So I have an issue with the transistors and don’t know how to trouble shoot it. There are only 3 connections on each so it seems like it should be simple and work. Guess I need to go back to the breadboard. Or duplicate all 3 transistors on a breadboard and run jumpers from the PCB to test. Total pain now it’s all soldered up.
Post a schematic. I told you how to fix the upload issue. Since you say it worked on breadboard and not on soldered proto board, please add close up images of the soldered board and everything around it.
So what's the connection between the 74HC959 and the 74HC595 ?
The first one doesn't come up anywhere and the second one comes up everywhere.
Did you just type in the wrong number ? Where did you get the number 74HC959 ?
Sorry I used the wrong PN.
The problem seems to be a decoupling capacitor and one stray 220k resister on the transistor base. Got a 220k mixed in with the 220ohm. Still need to verify this was the problem but it’s working on a bread board again and that’s the only difference I can see. Waiting for some ceramic caps to arrive in the mail. But when not lighting all the leds I see some artifacts on the led bar namely dull lighted sections. My only other concern is cross talk between wires but I am really not sure if this is possible on a 5v application. I ended up using a volt meter on every leg of the run and questing anything below 4v.
