Humble Electronics #012 - Inline exhaust fan 01.01

We exhaust our XTool M1 laser cutter out a window with the included tube. It's not perfect but works most of the time. When the wind is blowing towards the window, the smoke gets blown back into the house because there are fresh air intake vents on the underside of the laser case. We have avoided cutting on those days and it becomes a slight inconvenience. We've been looking at various ways to install an inline fan with the vent tube to make sure the smoke always blows outside. We've thought of using a computer fan or some other type of system that needs a bit of programming a microcontroller and a power supply. While able to be achieved, the cost may outweigh the benefit and we haven't committed to anything. My husband had some bee in his brain one morning this weekend and ordered this small USB powered fan from Amazon. I'm going to adapt this fan to our use. I don't recommend doing the same and I recommend just buying an inline fan. But, this blog isn't subtitled Humble Electronics for nothing. I like the challenge of using common items and parts in different ways. This is a current project that will take a few posts.

(image from the Amazon listing)

We got the fan in the same day he ordered it. We popped off the back panel and plugged it in. Pushing the single button on the back cycles through the speeds of low, medium and high. It does have a nice flow of wind and I'm thinking of getting one for myself. The unit has no LEDs or indications of the fan speed or if its powered and my husband wanted to be able to see that at a glance. I measured the change of voltage going to the motor and found it to be 5V, 7V and 9V. I think I can hook up some LEDs parallel to the motor input to show the voltage, hence the speed. I might also hook up an LED across the power input to show when it's connected to power.

The construction of the fan was nicer than expected. The back panel with the button, that we removed to measure the voltages, was very secure. The button itself was just a plastic surface with a small trace of plastic coming off of it and pressed onto a plastic pin in the back to work as a spring. The PCB was secured to the inside of the back compartment with two screws and a couple of plastic pins. The motor is connected, with a nice clip, to the PCB and secured by some hot glue so it wouldn't vibrate off. I removed the PCB and the motor connector. I drained the capacitor with a resistor, so it won't have a charge. My husband took off the stand by melting a hole in the covers over the pivot point and prying the covers off. Underneath the covers was a screw on each side that was removed and saved for later, if we need them, to attach the PCB or other parts. The front grill of the fan is made to be removed for cleaning and is easily removed when needed.

The fan is controlled by a microcontroller. Every time it is powered down, it no longer holds the last speed setting. We need access to the button on the back of the fan to control it. We decided, after some brainstorming, that I will lengthen the wire between the motor and the clip by splicing and soldering extra wire in. The wire will lead out to a control box holding the PCB. We did consider just bringing the button connections out but adding speed indicators changed that. The way we plan to proceed will also limit the wires coming out of the system to one pair, which should help keep the vent tube tight. The control box will be mounted just outside of the vent system, within 6 inches, hold the indicators and the PCB with button and the USB cord. I'm thinking of reusing the button that is on the back panel but I might just use another type. Next, I got to work on the LED indicators. 

I had seen a video where someone used the different colors of LEDs to indicate voltage. I hooked one LED each of red, green and blue (SMD ones, with no colored filters, that I had previously soldered together to use on a breadboard) in series and parallel. I used my variable voltage supply on the PAD-234 and powered them at 5V, 7V and 9V with 1kOhm resistors. I couldn't make it work the way I wanted. My mistakes were using too high value of resistor that was limiting the current down too much (I wanted my LEDs to be safe at 9V) and I didn't remember, in the video I watched, he didn't need a big spread. I went back and searched for the video, because I didn't save it to my electronics playlist. Thankfully, I had seen it just a short while ago and remembered the project involved. The video is linked here where he discusses his indicator LEDs. He was only looking at voltages between 1.7 to 2.5V and I need a higher and wider spread. I spent some time pondering over it and came up with a simple solution. 

This relates to some of my other LED projects where I run LEDs in parallel. I use a 5V supply in those and factor in only one LED and resistor in parallel. I remembered you need a higher voltage than 5V to drop across multiple LEDs in series. I set up a small breadboard with 3 parallel rows of LEDs that I had lying around. Each parallel row had a 1kOhm resistor and either 1, 2 or 3 LEDs in series. I hooked it up to my PAD-234 variable supply again and slowly raised the voltage. That finally gave me the start I needed. Each row lit up as the voltage was increased but they all lit at 7V. To shift the voltages higher I added an extra LED to each row. I actually used my SMD board again for the row of 4 LEDs because it is compact. I got it to work at the values I wanted, how I wanted. I still need to tweak the resistor values to equalize the brightness more but that will be done with the final board. This meter seems to only register a current starting at 0.04A. It looks like my total current is under that so I hope it doesn't effect the system too much. I'll test it before closing everything up.

(As a side note mostly for myself, because of the refresh rate of the meter screen, I could not get a good photo from a viewing distance with my phone. The screen on the meter would often be blank or only showing some numbers. As I physically moved my phone in closer, the numbers stabilized.)

I can replace the string of LEDs with other diodes that have an equivalent dropping voltage. The only problem with that is, I only have through hole devices so they would take up a lot of space. To make it compact and lightweight, I'm going to use some small SMD LEDs that I already have. Soldering those to a prototype board will make a nice display. I don't know if there is another way to do this. I suspect there may be, using some other type of diode, but that will be an investigation for another day. Our idea is to design the box cover with a cutout in a triangle that will be filled with resin as a diffuser for the speed indicator display.

Next step is soldering up the board. Then I'll test how the system runs with the extra load. That makes 2 more posts plus the box design. In the meantime...

Happy Making,

Michelle