Humble Electronics #013 - Inline Exhaust Fan 01.02

I soldered up a board with the speed indicator LEDs so I could test it and see how much space it took up. I also needed to test resistor values to get an even brightness and then test it with the system. 

I started with a section of prototype PCB that I figured would fit what I needed. Each of my 1205 SMD LEDs just fit between the holes on the board. I filled each hole for the LEDs with a bit too much solder. Getting the LEDs on the bumps was really hard and it looked messy too. 

Regardless, it worked after I connected each row on the underside with solder. I put some resistors on a small breadboard. I hooked them up to each row with some alligator clips on wires extending the power and ground. I tested out different values at the three voltages I needed, 5V, 7V and 9V, to get the brightness fairly even and to not get too high of a current at 9V. I settled on a resistance of 470 Ohm for the top blue row, 1.22 kOhm for the middle green and white rows and 360 Ohm for the red power indicator.

 

I ran into one problem. The last time I worked on this indicator, I used a multi-colored LED board for the forth row. It lit up perfectly at 9V. However, the row of four blue LEDs would not light up at 9V. It needed 10V to light up. The voltage drops across the multi-colored LEDs was smaller than across the four blue LEDs because the red and yellow ones light up at under 3V. This took a little bit to figure out and at first I thought my soldering was not connected because it looked funky. Then I raised to voltage and all four LEDs lit. Instead of removing the last LED in the row, I just skipped it and soldered my ground wire in between the last two LEDs. This worked like I wanted, mostly. I did want the rows to have different numbers of LEDs to match the speed indicator but it diffused nicely.

I soldered the resistors to the board, but hanging off. It looked ugly but it was ready to test on the motor. I temporarily soldered some wires between the indicators and the motor supply. I left off the wire from the power to the power indicator LED for now. It worked well and didn't seem to cause any problems. It should be drawing under 40mA, 36mA by my calculations, for the speed indicators because it didn't register on my V/A meter. This was an inexpensive fan so if we blow it, its easily replaceable.

Neither of us were happy with the results, mostly because it was a bit of a mess. I decided I was going to make a new one from a whole PCB prototype board so I can add the resistors to it and change the number blue LEDs. In order to get the different number of LEDs per row and keep them turning on when we wanted, I placed one white and one green LED a little more separate from the others. They will be behind a small wall I'm installing in the box. When I soldered this board, I placed the LED down on the board and added the solder. The LEDs were a bit squirrely but they came out straighter and excess solder bulged on the underside where it was used for connecting wires. I placed the resistors on the underside because I wanted the board to be lifted off the bottom of the box it will sit in. This will give me some space to cover over the bottom wiring with hot glue to reduce shorts. I also didn't have a box idea yet so this will give me some room on the top for the main board. The new board looks great and worked. The three blue LEDs still did not come on at the same time as the three green LEDs because it needs that little bit of an extra bit of voltage, times three, to activate.

Next up is the container for the control box in a laser cutter post. It is coming along nicely. In the meantime....

Happy Making,

Michelle