Tuesday, 24 June 2014

2 x 2 SMD LED Matrix

Today my new 48W Soldering Iron Controller arrived in the post. For just $28.45 on eBay, this is essentially the same iron that is being sold elsewhere for up to $50. The iron came from Sydney, so I’m protected by Australian Consumer laws, so I didn’t feel like it was very risky. Turns out, I’m right. The soldering iron seems to work just fine.
I turned my hand to two projects with the new iron.
In the post today, I also got my new 16x2 character LCD “LCD HD44780 1602 16x2 Character Display Module Blue Blacklight For Arduino” that I also bought on eBay (for $3.42 AUD). The LCD needs to have some header pins (16) soldered in so that you can connect it up to a solderless breadboard. This was no problem at all with the new soldering iron. The solder flowed very well and the iron heated up fairly quickly. I’m happy about that. No pictures of the LCD yet, I’m going to post separately on that later on.
The main thing that I wanted the temperature controlled iron for was so that I could try my hand at some SMD soldering.
A while back, I posted an article mentioning the SMD version of a 4 x 4 through hole component LED matrix (4 x 5 LED PCB) where I said that I was going to have a go at SMD at some later date … well, today is the date.
The circuit is simply a rework of the 4 x 5 matrix using SMD instead of through hole components. Also … it is only 2 x 2 (4) 0805 Super Bright LED, rather than 20.
Picture 64
You can see that my soldering isn’t all that neat, but on a circuit this small, it is neat enough. There are 4 x Super Bright White LED and 4 x 120Ω resistors. The SMD form factor is 0805, so they are about 2mm x 3mm in size (more or less). I also have a 9V battery snap soldered in to the circuit. 9V is a probably a bit high and I don’t have much hope that the circuit will last very long before it burns itself out. After a minute or two of power, the circuit is uncomfortably hot, it may be that I can sacrifice some lumens and increase the resistor size to give it a more comfortable lifespan.
I wanted a small light that I could attach to my magnifying glasses to help illuminate my work. I plan to mount the light in a white resin plug to diffuse the light somewhat …now I’m concerned that the resin will not be much use if the resistors burn up. Meh.
Picture 65
When powered, the LED are indeed Super Bright.
While I was soldering the LED in place, the technique that I used with these fiddly components was:
  1. lay the component down on the work mat
  2. Using the multimeter, work out the correct orientation for polarity
  3. Pre-solder the pad on one side
  4. Hold the component onto the solder with some spring tweezers
  5. Apply heat.
When the solder is hot enough to flow, the tweezers squeeze the component down to the board and the solder holds the component in place. After that, it was just a matter of soldering the other end down and then using some solder wick to tidy the job a bit.
I was thinking later that I could have used a small heat proof straight-edge to align the components in a more tidy way.
I need to get some more hydrogen peroxide and hydrochloric acid so that I can make another couple of boards, I’ve run out (pooh).
I’m still going to go ahead and mount the circuit in resin. But the next version of this circuit will use a smaller power supply and/or a greater sized resistor.
I need more practice at SMD hand soldering, but for now, I’m happy with the results.

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