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 I'd like to think I know what I'm doing, but...

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Kebii'tra Verda


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I'd like to think I know what I'm doing, but...
« on: Aug 20, 2013, 07:43 AM »
...I'm stumped.

I've grown up around home made electronics. I've been able to decipher and put together small circuit designs since I can remember. I've even been able to figure out how to slightly modify some designs to make them work the way I want them too.

But I found a circuit design a few months ago that has me stumped. I have checked and rechecked the components, tried changing out some I thought may have been either bad or wrong, traced the path of each and every line several times to make sure they were installed correctly...

and the dang thing still doesn't work. Grr.. :'(

Here is a pic of the circuit:


The IC4017 chip usually makes each of the 10 LEDs light up in sequence 1-10, but only one LED at a time. The general idea behind this design is the added SCRs serve to hold the charge on the LED to make it stay lit until all are lit, and then they are supposed to all go out and the process start all over again.

Component list:
R2 and R3 are 10K ohm
all other Rs are 1K ohm
VR1 and VR2 are 47K ohm variable resistors
all caps are 10uF, 25V
All SCRs are BT169
IC1 is a 4017
LEDs are maker's choice

He does not give a suggestion for the T1, T2, and T3, but in reading, he specifically says T3 is a PNP transistor. Nothing specific is said about T1 or T2, but it can be implied by the schematic that they are similar. So all three are PNP transistors.

Here's what I built:

Closeup of the board:

When the battery is first attached, this is all that lights up:

When the IC is pulled out and shifter around a few times (but not fully seated back into the socket) like this:

I can get all ten of the graph LEDs to light up:

But the two independent LEDs on the lower right will only flash for a split second.

Also, the variable 47K ohm resistors have no effect on anything.

I know this is a jumbled mess. My hope was to create the chasing bar graph LED for an addition to my costume. But for the life of me, I cannot figure this out!

Any help would be appreciated.

daVID.

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#0127a Kebii'tra Verda
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Dresdon Acacin


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Re: I'd like to think I know what I'm doing, but...
« Reply #1 on: Aug 20, 2013, 07:50 AM »
What you may have to do is chech your soldered connections. Dremals can help in isolating connections that might be bridged or something...at least that's what I have to do with my 140W well since its a bit excessive and imprecise for this kind of work :/

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Kebii'tra Verda


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Re: I'd like to think I know what I'm doing, but...
« Reply #2 on: Aug 20, 2013, 08:06 AM »
Yeah, I've checked that even with a magnifying glass to make sure nothing is crossed and I can't see anything that would be a problem.

daVID.

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Dresdon Acacin


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Re: I'd like to think I know what I'm doing, but...
« Reply #3 on: Aug 20, 2013, 08:24 AM »
I know exactly how you feel....then once you figure it out your kicking yourself >.<

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Re: I'd like to think I know what I'm doing, but...
« Reply #4 on: Aug 21, 2013, 05:34 AM »
I don't know if this helps, but looking a quick glance at that schematic, T1 and T2 are NPN transistors, only T3 is a PNP. I'll look again when I wake up but that may be the issue you're having.

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Kebii'tra Verda


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Re: I'd like to think I know what I'm doing, but...
« Reply #5 on: Aug 21, 2013, 07:20 AM »
I don't know if this helps, but looking a quick glance at that schematic, T1 and T2 are NPN transistors, only T3 is a PNP. I'll look again when I wake up but that may be the issue you're having.

Okay...now that you mention it, I just now noticed that on T1 and T2, the "arrow" showing power flow is pointing out, not in like T3.

Off to the 'Shack I go.

But the next question is...there are so many different types of npns. Which one do I get...

daVID.

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Re: I'd like to think I know what I'm doing, but...
« Reply #6 on: Aug 21, 2013, 02:51 PM »
Off the top of my head I couldn't recommended any specifically, but I would recommend seeing which fit best into the circuit properties. I have some circuit resources that I can check, I'll let you know what I can find out, hopefully before work this afternoon.

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Kebii'tra Verda


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Re: I'd like to think I know what I'm doing, but...
« Reply #7 on: Aug 21, 2013, 06:16 PM »
I'm going to start with the same size and configuration as the ones I already have. The simple half-rod look, not the ginormous ones I saw (with screw-down heatsinks). I won't be going to the Shack until tomorrow, so I probably won't have an update until then.

daVID.

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Re: I'd like to think I know what I'm doing, but...
« Reply #8 on: Aug 21, 2013, 07:04 PM »
Ok, I've got some transistors at home from when I went through avionics school. I'll check those and see if I can give you a number, but that won't be for close to 8 hours.

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Kebii'tra Verda


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Re: I'd like to think I know what I'm doing, but...
« Reply #9 on: Aug 21, 2013, 07:05 PM »
That's fine. I won't be heading out to the Shack for about 15 hours... ;D

daVID.

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Re: I'd like to think I know what I'm doing, but...
« Reply #10 on: Aug 22, 2013, 03:40 AM »
The transistors I still have from school that are NPNs are both 2N3904. http://en.m.wikipedia.org/wiki/2N3904 has some info. I hope that helps. I'm not sure what the current in your circuit is, but that one should work. If its a higher current look for a 2N2222 would work...but I doubt this circuit has the current to make that a good choice. If that doesn't get it going right, let me know and I'll see if I can virtually troubleshoot it.

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Kebii'tra Verda


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Re: I'd like to think I know what I'm doing, but...
« Reply #11 on: Aug 22, 2013, 07:37 AM »
Yep, those are the ones I was looking at. I'm using a 9V source.

Thanks for the info!

daVID.

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Thaxos


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Re: I'd like to think I know what I'm doing, but...
« Reply #12 on: Aug 22, 2013, 02:02 PM »
I concur on the 2N3904 for NPN.
3906 is your PNP.

Those should do just fine for this type of project, they're the go to transistors for typical stuff like this.

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Re: I'd like to think I know what I'm doing, but...
« Reply #13 on: Aug 22, 2013, 02:45 PM »
Thaxos is right on the 3906, forgot to mention that. Let us know if that gets the circuit on track. I was looking at using a LED bar graph display thing once I got to wiring up my electronics, so this is good to see.

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Kebii'tra Verda


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Re: I'd like to think I know what I'm doing, but...
« Reply #14 on: Aug 22, 2013, 04:10 PM »
Well, osik.

I changed out the two incorrect PNPs for NPNs...and nothing.

Now no lights on the bars are coming on.

I did install a switch inline with the battery, and now the only thing that is happening is the two extra LEDs inline with R4 are flashing for just a split second.

Dang it...I'm going crosseyed trying to figure this out.

daVID.

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#0127a Kebii'tra Verda
267th Brigade "Remo's Raiders"
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