Part of the reason why I didn't like it was that it required batteries, another part was that it's a lot bulkier than it needed to be, and the last is that the IC holder is meant to be put through a perfboard and not a plastic box.
The newer version of the board was being used for the prototype of a different project, but the electrical engineer decided to add some more parts to it to reduce the load of the voltage regulator on the main board. When he received the prototype boards, I was to remove the board from the main board and toss it into the electrical waste bin.
With a fully-functioning LM317 on the board, there was no way I could do that, so I (painstakingly) de-soldered the voltage regulator and one of the 8-pin headers from it before storing the board elsewhere if i needed the other parts from it.
One of the two outdated boards I took home already had parts on it (I didn't realize it was an outdated board until I noticed the missing diode (how I missed it when I was putting the SMD parts on, I haven't a clue) and brought it to the attention of the electrical engineer, who told me it was the older revision of the board (the board that superseded it has ".B" marked with the part number). I had left it alone, since I didn't want to just toss it in with the electrical waste, so I held onto it until I needed it.
The board is the board that sits between the main board and LCD panel (that is made by some other company that we purchase), and was going to be much easier to use than the old prototype board that I used for the adjustable voltage regulator project because of the "built-in" spot for the LM317.
The first thing I had to figure out was what voltage to output so that an LED with a 3.3 volt forward voltage and an LED with a 1.6 volt forward voltage can agree on. With the adjustable voltage regulator, I toyed with it a bit before doing some maths to find that 2.5 volts should be a decent median for both types.
The initial test was fine, and I found it quite nice that it was the exact same resistor value needed for 2.5 volts (Vout=1.25 * x/x), so whatever I was able to find (between 100 and 1k ohms) for the power LEDs would work just fine.
The board has three spots for LEDs, one for power, one for use indication, and one for reversed power. For my case, I only needed two of the three LEDs, but I figured I might as well use all three; I set up the central LED to be the power and the outer LEDs to be a reversed power indicator (so that it's quite obvious if the LED testing board is plugged in "backwards".
With some calculations, I figured I'd need a resistance of about 500 ohms for each of the power indicator LEDs (since I'm running it off of 12 volts), so my best bet would be to either find a resistor close to 500 or to put two 1k ohm resistors in parallel (which is theoretically easy with SMD). When I dug around at the unused parts during lunch, I found the 1k ohm resistors and held onto them as I dug around more. I then found a 700-something ohm resistor reel (remember, this are SMD resistors) before finding 600-something ohms, but then I was quite elated when I found 475 ohm resistors and proceeded to put the other two reels away.
On the board, the two outer LEDs use SMD resistors with a 1206 case code and the centre one uses 0805, which was something I was partially looking for, but because I was able to use the 0805 sized resistors in the 1206 slot, I didn't have a need for the 1k ohm resistors that I brought home with the 475 ohm resistors.
I soldered most of the components onto the board and soldered the LM317 on the "wrong side" (but in the correct pin order) to make the bottom as minimalistic as possible. The next day I thought of adding some diodes to protect the circuit and LEDs so that when the board is hooked up incorrectly, the voltage regulator circuit is protected, and when the board is hooked up correctly, the reversed polarity LEDs are protected. After getting home, I added the diodes in and hooked up the jumper wire to make it work and it did indeed work.
Except for one little problem: the LM317 became really hot even though the output voltage was correct. When I soldered the LM317, I soldered it so that the plastic side was against the board and the tab was in the air, and so I though maybe I needed to actually solder it to the correct side so that the pad on the underside of the board can absorb the heat. I moved the LM317 to its correct position on the board, but nothing changed, it was still getting hot.
I poked with the adjustable voltage regulator project and the tab didn't get hot at all - not even slightly warm - and so I decided to think for a bit. I decided to double check the power path and found that I had not added the jumper wire that connected the ground to the actual ground pin, and after remedying the problem, all was well.
I forgot to mention that I put some header pins into the unused ports of the header to make it obvious which of the header holes to use. I also marked an arrow on the board pointing toward the positive hole, but since it is on the "outside" side of the header, it can't be seen in the following pictures.
Finished top and bottom.
Board has power and is plugged in correctly; board has power, but has power is reversed; board showing an LED being tested.
I forgot to cover the point of the device (and it's convoluted predecessor), which is to test if LEDs are working (which is probably fairly obvious) and to be able to discern the LED's colour (for clear or frosted LED cases). Before having a case that allowed me to organize my LEDs by colour (and case type), it used to be thrown together in a section of another case. This obviously made it horrible because I had to check the colour of the LED every time I needed one.
The first version of the preceding LED tester used a 9 volt battery, the project box, a resistor, and the IC holder - it did the job when I needed it. Eventually I changed it so that it ran off of a pair of AA batteries so that it would be easier to replace the batteries (whenever that would happen) and to reduce the voltage delivered to the LED being tested greatly. For the second version, I also added one of those plastic battery pull-tabs that come with some electronics with pre-installed batteries, so that the drain on the batteries would be further slowed down from air-based discharge (probably really unnecessary, but why not?)
While preparing an LED for the picture, I blew up a dual-coloured LED that was going to be used for my soldering light/fan switchbox, but luckily there were plenty spares at work, since it no longer being used.
The diodes I used are the 4007 (the one further away from the header) and the 5817 (one closest to the header) since that's all I had at home that would be easy to use.
The things I learned from this project is to check the paths before checking the parts, and to keep the LED in the tester for the minimum amount of time so that it doesn't blow up.
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