First soldering project-LED Christmas tree.

Thread Starter

droggie

Joined Oct 21, 2012
137
Hi guys. I’m about to start my first soldering project and I have a couple of questions.
It is an LED Christmas tree. I’ve attached the board and the schematic.

1. How do I tell which side is the cathode on the schematic?
2. Can I solder the resistor any way; or is there a polarity?
3. And how does the electricity travel from each soldered point to another?
 

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ErnieM

Joined Apr 24, 2011
8,041
1. How do I tell which side is the cathode on the schematic?
I remember it like this: The Anode is the side of a diode symbol that looks like the Letter A, and the Cathode (Kathode) is the side that looks like the letter K.

Anode -|>|- Cathode

The LEDs go in the board by matching the flat side to the silk screen.

2. Can I solder the resistor any way; or is there a polarity?
No polarity, they go in either way. You may want to make them all go the same way for looks. Professionally that is common for "inspection."

3. And how does the electricity travel from each soldered point to another?
The back of the board (your right most picture) shows copper left on the PCB that conducts where it is needed. It is covered by a green coating to protect it from shorting.
 

KJ6EAD

Joined Apr 30, 2011
1,569
When you solder the capacitors and transistors, tack one lead with minimal solder then adjust the alignment of the part by gently bending the soldered lead before soldering the other lead(s) then go back and complete soldering of the first lead.
 

tracecom

Joined Apr 16, 2010
3,944
And I suppose you know, but just in case, remember that the parts go on the side with the white drawings and lettering and the soldering all is done on the side with the copper pads exposed.
 

Thread Starter

droggie

Joined Oct 21, 2012
137
I have soldered all of the resistors, capacitors and transistors. Is there anyway I can test that there LEDs will function properly with the use of a breadboard or something?
 

tracecom

Joined Apr 16, 2010
3,944
I have soldered all of the resistors, capacitors and transistors. Is there anyway I can test that there LEDs will function properly with the use of a breadboard or something?
You can use a 9V battery and a 1k resistor. Just don't connect the LED without the resistor.

Positive terminal of the battery to one side of the resistor, the other side of the resistor to the anode of the LED, and the cathode of the LED to the negative terminal of the battery.
 
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Thread Starter

droggie

Joined Oct 21, 2012
137
Everything is soldered but the LEDs. Can I just touch an LED to one set of the copper points, or do I have to solder them all in series. And I do not get the A or K example. There are arrows pointing left and arrows pointing right. Which is the negative and which is the positive?
 

KJ6EAD

Joined Apr 30, 2011
1,569
You can use a 9V battery and a 1k resistor. Just don't connect the LED without the resistor.
It would be safer to use a 3.3k or 3.6k resistor. Those are low current LEDs as is typical of many of the Velleman kits.

Everything is soldered but the LEDs. Can I just touch an LED to one set of the copper points, or do I have to solder them all in series. And I do not get the A or K example. There are arrows pointing left and arrows pointing right. Which is the negative and which is the positive?
Don't try to connect a single LED without the others in it's series. They divide the voltage among themselves and one alone would get too much voltage and therefore too much current, possibly being destroyed. The pointed end of the LED symbol with the bar across it is the cathode (negative) end. The small arrows indicate the emission of light to differentiate the symbol from other types of diodes but the direction of them isn't relevant.
 
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KJ6EAD

Joined Apr 30, 2011
1,569
No, they connect anode to cathode or vice versa in a series but you can just reference the white silkscreen markings on the board to see the flat edge of the LED is the cathode. Check my last post for edits also.
 

Thread Starter

droggie

Joined Oct 21, 2012
137
What bars? The only bars I see are the transistors. I only see the LED symbol with either left or right arrows.
 

Thread Starter

droggie

Joined Oct 21, 2012
137
Can I reference from the capacitors? For example, make sure the anode's path follows to the positive terminal of the capacitor and so on?
 

KJ6EAD

Joined Apr 30, 2011
1,569
You're overcomplicating it and the positive ends of the capacitors are each connected to the cathode of an LED.

The bar is part of the LED symbol on the schematic.
 

kubeek

Joined Sep 20, 2005
5,724
And how can I reference from the silk screen. I am confused.
Just look at the siklscreen on the board, for example LD7, the circle has a flat side next to one of the leads. The LED that you will solder in also has a flat side. Put it in the circuit like the silkscreen shows you.
 

Thread Starter

droggie

Joined Oct 21, 2012
137
Sorry KJ6EAD, I got it thanks a lot. However when I soldered the power supply, I did not strip enough wire, and both wires easily got ripped out. I do not think this desoldering pump I have is any good. Any help?
 

Thread Starter

droggie

Joined Oct 21, 2012
137
Also, is the "flat" term universal for all LEDs? Meaning the flat part indicates the cathode is to be soldered on the flat side?
 

KJ6EAD

Joined Apr 30, 2011
1,569
What desoldering pump, the one in the Radio Shack soldering starter kit?

Also, is the "flat" term universal for all LEDs? Meaning the flat part indicates the cathode is to be soldered on the flat side?
Not all LEDs have the flat, but when they do it indicates the cathode side. You can also tell the cathode lead because it's shorter than the anode...unless the leads have been trimmed.
 

tracecom

Joined Apr 16, 2010
3,944
I managed to desolder both points, but I took the copper surrounding with it. Any solutions?
Sure. It can be fixed, but it requires that you carefully scrape away the green solder mask from the track that went to the pads that you pulled off. Be careful to scrape only the green part; leave the copper track on the PCB. Then, you can solder the wires directly to the track. If the hole for the wire is big enough, feed the insulated wire through far enough so that you can tie a knot in the wire before you solder it. This will provide some strain relief, so that the wire will be held to the PCB by the knot instead of it pulling against the solder.
 
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