Introduction: Dust Collector Full Detector

About: Hiking, Woodworking, PCB design using Eagle, Writing Software for MacOS and AVR, 3D Design using Fusion 360

If you have a dust collector you know what a pain it is if the shavings backup into the filter. Some of the commercial detectors available are expensive and they rely on an optical sensor. Who would put anything optical inside a drum full of statically charged dust and shavings and expect it to work reliably?

The PCB I designed determines when a dust collector drum is full by detecting when a small DC motor driving a paddle inside the drum slows down due to shavings restricting the paddle.

How it works:

There is no on/off switch on the board, a switching power supply that powers the board is connected to the dust collector’s motor control relay. The board is only active when the dust collector is running. You have to turn the dust collector off to empty the drum so the board is reset by turning the dust collector off and on.

The mcu used is an ATtiny84A. The mcu monitors the voltage drop across the motor driving the paddle within the drum. When the voltage drops below a predefined level the drum is full.

When the drum is full:

- The motor in the drum is turned off using a N-channel MOSFET. The design includes a flyback diode in parallel with the motor to provide a dissipation path for the energy stored in the motor at the moment that it’s turned off.

- A strobe light is activated using another N-channel MOSFET.

- (optional) A message is sent using an RFM69CW transceiver. Noted as optional because the board works with or without the RFM69CW transceiver installed.

If a message is sent, the message is received by a companion board I designed that will send the message “Dust collector full” to my hearing protector that has a built-in FM radio. See

The board contains a DC-DC module to supply 5V power to the motor and to a 3.3V regulator on the board that powers the mcu and the optional transceiver.

The overall board is powered by an AC 120-220V to 12V DC switching power supply. The strobe is a 12V device.


I initially thought that the paddle would be in the way when emptying the drum and eventually it would snap off. I’ve been using it for over a year and because of its location on the drum cover, the paddle stays out of the way. I use it on a wall mounted dust collector. The drum on my collector is on wheels. The cover is light, it lifts up and you move the drum out from under it. I don’t think this solution would work well on a portable dust collector where you lift the motor attached to the drum cover off in order to empty it. You would need to devise some way to protect the paddles when placing the cover on the floor.

The schematic is enclosed in the next step.

As with the other boards I’ve designed, this board’s gerber files are shared on PCBWay.

There's a new version of this project that monitors the filter in addition to the bin level.

The 3D part STL files are available on Thingiverse:

This board was inspired by an article by William F. Pentz, although I did not use his design:

Step 1: Instructions for Assembling the Board

Instructions for assembling the board (or almost any small board) follows. In the following steps I'm assembling a board with the optional RFM69CW transceiver.

If you already know how to build an SMD board, skip to step 13.

Step 2: Gather Parts

I start by taping a piece of paper to the worktable with labels for all of the very small parts (resistors, capacitors, LEDs). Avoid placing capacitors and LEDs next to each other. If they mix, it may be hard to tell them apart.

I then populate the paper with these parts. Around the edge I add the other, easy to identify parts.
(Note that I use this same piece of paper for other boards I've designed, so only a few of the locations in the photo have parts next to/on the labels)

Step 3: Mount the Board

Using a small piece of wood as a mounting block, I wedge the PCB board between two pieces of scrap prototype board. The prototype boards are held to the mounting block with double stick tape (no tape on the PCB itself). I like using wood for the mounting block because it’s naturally non-conductive/antistatic. Also it’s easy to move it around as needed when placing parts.

Step 4: Apply Solder Paste

Apply solder paste to the SMD pads, leaving any through hole pads bare. Being right handed, I generally work from top left to bottom right to minimize the chances of smearing the solder paste that I’ve already applied. If you do smear the paste, use a lint free wipe such as those for removing makeup. Avoid using a Kleenex/tissue. Controlling the amount of paste applied to each pad is something you get the hang of through trial and error. You just want a tiny dab on each pad. The size of the dab is relative to the size and shape of the pad (roughly 50-80% coverage). When in doubt, use less. For pins that are close together, like ICs in a TSSOP package, you apply a very thin strip across all of the pads rather than attempt to apply a separate dab to each each of these very narrow pads. When the solder is melted, the solder mask will cause the solder to migrate to the pad, kind of like how water won’t stick to an oily surface. The solder will bead or move to an area with an exposed pad.

I use a low melting point solder paste (137C Melting Point)

Step 5: Place the SMD Parts

Place the SMD parts. I do this from top left to bottom right, although it doesn’t make much difference other than you’re less likely to miss a part. The parts are placed using electronics tweezers. I prefer the tweezer with a curved end. Pick up a part, turn the mounting block if needed, then place the part. Give each part a light tap to ensure that it’s sitting flat on the board. When placing a part I use two hands to aid in precise placement. When placing a square mcu, pick it up diagonally from opposite corners.

Inspect the board to make sure any polarized capacitors are in the correct position, and all chips are oriented correctly.

Step 6: Time for the Hot Air Gun

I use a YAOGONG 858D SMD Hot Air Gun. (On Amazon for less than $40.) The package includes 3 nozzles. I use the largest (8mm) nozzle. This model/style is made or sold by several vendors. I’ve seen ratings all over the place. This gun has worked flawlessly for me.

I use a low temperature solder paste. For my model gun I have the temperature set to 275C, airflow set to 7. Hold the gun perpendicular to the board at about 4cm above the board. The solder around the first parts takes a while to start melting. Don’t be tempted to speed things up by moving the gun close to the board. This generally results in blowing the parts around. Once the solder melts, move on to the next overlapping section of the board. Work your way all around the board.

Step 7: Reinforce If Needed

This board has nothing that needs to be reinforced, but if the board you’re working on has a surface mounted SD card connector or surface mounted audio jack, etc., apply extra wire solder to the pads used to attach it to the board. I’ve found that solder paste alone isn’t generally strong enough to secure these parts reliably.

Step 8: Cleaning/removing the SMD Flux

The solder paste I use is advertised as being “no clean”. You do need to clean the board, it looks much better and it will remove any small beads of solder on the board. Using latex, nitrile, or rubber gloves in a well ventilated space, pour a small amount of Flux Remover into a small ceramic or stainless steel dish. Reseal the flux remover bottle. Using a stiff brush, dab the brush in the flux remover and scrub an area of the board. Repeat till you’ve entirely scrubbed the board surface. I use a gun cleaning brush for this purpose. The bristles are stiffer than most tooth brushes.

I pour the unused flux remover back in the bottle. I don’t know if this is correct or not. I haven’t noticed any issues related to doing this.

Step 9: Place and Solder All of the Trough Hole Parts

After the flux remover has evaporated off the board, place and solder all of the trough hole parts, shortest to tallest, one at a time.

The DC-DC converter is attached to the board using four 2 pin headers. Don't cut one pin each of the two pairs of pin headers on the converter output pads used to attach the converter to the board. This will make it easier to adjust the converter.

Step 10: Flush Cut Through Hole Pins

Using a flush cutter plier, trim the through hole pins on the underside of the board. Doing this makes removing the flux residue easier.

Step 11: Reheat Through Hole Pins After Clipping

For a nice appearance, reheat the solder on the through hole pins after clipping. This removes the shear marks left by the flush cutter.

Step 12: Remove the Through Hole Flux

Step 13: Apply Power to the Board

Apply power to the board (12V). If nothing fries, adjust the DC-DC converter to output 5V. Verify that you have 3.3V from the large tab on the regulator chip on the board.

At some point you'll also have to adjust the 12V switching power supply to output 12V.

Step 14: Set the ATtiny84A Fuses

This step sets the processor speed and clock source. In this case it's 8MHz using the internal resonator.

I do this using an ISP, specifically the one I designed. See You can use any AVR ISP such as Arduino as ISP built on a breadboard. See the Arduino as ISP example from the Arduino IDE Examples menu.

These are Mac OS instructions. I'm not a Windows user.

For this step, you could probably do this from the Arduino IDE via "Burn Bootloader", but I prefer to do this from a BBEdit worksheet (you could also do this from a Terminal window)

Connect the ISP cable from the ICSP header on the board to the 3v3 ISP. Set the DPDT switch near the ICSP header to "PROG".

Very important: You must use a 3v3 ISP or you may damage components on the board.

If the ISP is supplying power, disconnect power from the board. I use a 5 wire ISP cable rather than a 6 wire cable. The 5 wire cable doesn't provide power. This way I can make changes to the software without having to remove/provide power to the board between uploads.


# ATtiny84A 8Mhz, internal clock

/Applications/Arduino\ -C /Applications/Arduino\ -p t84 -P /dev/cu.usbserial-A603R1VD -c avrisp -b 19200 -U lfuse:w:0xe2:m -U hfuse:w:0xdf:m -U efuse:w:0xff:m

/dev/cu.usbserial-A603R1VD above should be replaced with whatever USB serial port is connected to the ISP.

Step 15: Upload the Sketch

If you've never used an ATtiny mcu, you need to install via the Arduino Boards Manager (Tools->Board->Boards Manager), the attiny package by David A. Mellis. Search for ATtiny in the Boards Manager window. If the package doesn't appear, then you need to add "" to the Arduino Preferences - Additional Boards Manager URLs. Go back to the boards manager window to install the package.

Once the package is installed you then need to download the attached to this step. You can either mix these sources into your Arduino folder or change the Sketchbook Location in the Arduino preferences to point to these sources. The preferred method is to keep these sources separate.

Set the board (Tools->Board) to ATtiny24/44/84. Set the Processor to ATtiny84, and the clock to internal 8MHz.

If you haven't already done so, set the Programmer (Tools->Programmer) to Arduino as ISP.

Get the DustCollectorFullRFM69 sources from the GitHub repository Arduino-Tiny

Compile the DustCollectorFullRFM69 sketch. If that goes well, upload the sketch using the same wiring and ISP used to set the fuses in the previous step.

Step 16: Print the 3D Parts

Download and print the 3D parts from

These parts were designed using Autodesk Fusion 360

Box.stl 20% fill, support all

Clamp.stl 80% fill, no support

Cover.stl 20% fill, no support

CoverWithStatusLEDs.stl 20% fill, no support

Motor Mount.stl 20% fill, support touching bed

2 x Paddle.stl 20% fill, no support

If you don’t own or have access to a 3D printer, Thingiverse has a 3D print service. I’ve never used it and I have no idea what it costs.

Step 17: Build the Cable Assemblies

Follow the instructions in the photos to build:

- Board to motor cable

- Status LEDs cable

- Motor cable (shown attached to motor)

- Strobe cable (The strobe comes with a bonded cable. You just need to trim its length and add a connector.)

- 12V DC power cable

- AC power cable

If you've never crimped an XH pin before see step 20 from my Varmint Detector intstructable:

Step 18: Test the Board and Cables

Obviously easier to test the board and cables now rather than when they're installed.

Continuity test all of the cables pin to pin to verify that there are no broken wires (generally due to improperly crimped pins.)

Hookup all of the cables as shown.

Apply 12V. (In the photo I'm using my bench power supply.)

With power applied, grip the motor body with one hand and the threaded motor shaft with the other and try to stop the shaft from turning. At some point the strobe should start flashing. If you can't stop the shaft, try mounting the paddles. You'll have more leverage with the paddles mounted.

When the motor stops the strobe should start flashing. If you're also testing with the Audio Alert I designed, you should hear a message stating that the dust collector is full.

I haven't encountered too many problems. I've built a few extra boards including the board for this instructable. I've had a bad MOSFET. The motor wouldn't run and the strobe immediately started to flash.

Step 19: Insert the Motor Into the Motor Mount

Carefully insert the motor + cable assy into the 3D printed motor mount. If you look into the slot for the motor you should see a T shape at the bottom of the shaft. The goal is to get the wire folded over the end of the motor into this T slot. If you've cut the cables exactly as stated in the cable assembly photo, the connector will sit in the connection slot as shown in the photo above. If the cable is the correct length yet it extends too far into the connection slot, the problem may be that you didn't get the wire into the T shaped pocket in the bottom of the motor slot.

Step 20: Connect Control Box to Motor Cable

Connect the control box to motor cable with the drain wire folded back over the wire sheathing. Apply a dab of plastic epoxy to the sheathing where it comes in contact with the motor mount. Set the assembly aside and wait for the epoxy to cure.

Step 21: Mount the Motor Mount to the Drum Cover

Vacuum the drum cover.

Drill three 3.2mm holes in the drum cover using the drilling template provided. Position the motor mount template in a location that generally gets lifted higher than the rest of the cover when emptying the drum. For me that is as shown in the photos. I've yet to come close to damaging the paddles and shaft.

Vacuum the drum cover and clean the surface with window cleaner.

Place a bead of silicone as shown on the motor mount.

Secure the motor mount to the cover using two stainless steel M3x8 pan head self tapping screws with M3 washers (regular threaded M3 screws will also work)

Wait for the silicone to cure.

Position the paddles on the motor shaft with the paddles flush with the end of the shaft. Secure the paddles using six stainless steel M3 x 16 screws with washers and nuts.

Step 22: Assemble and Locate the Control Box

Attach the 12V DC power cable and AC cable created in step 17 to the 12V switching power supply as shown in the photo.

Install the 12V power supply by snaking the cut end of the AC cable through the hole shown in the photo. Use 2 stainless M3x6 button head screws to secure the power supply to the box.

Using 2 stainless M3x14 button head screws, washers and nuts, attach the AC cable clamp.

Install the control board using 4 stainless M2x5 button head screws.

Install the strobe/flasher to the cover using 2 stainless M3x8 flathead screws.

Press fit the status LEDs into the holes on the cover (left to right Blue Yellow Green)

Run the green drain wire from the AC cable to the board (bottom right)

Attach the 12V DC power, strobe and status cable to the locations noted in the photo.

At some point the cover will use a stainless M3x6 button head screw to secure the cover to the box.

Disclaimer: Modification of your dust collection electrical control system should only be performed by a qualified electrician. Improper modifications may cause physical harm to you and/or your equipment and may void your dust collector warranty.

When your electrician opens the dust collector AC power control box, they will see the wire feeding the dust collector motor. The AC power cable from the detector control box will attach to these terminals and the common ground.

AC relay control boxes are all pretty similar. The photo shows what mine looks like inside and where I made connections. Note that insulated terminal lugs sized for the wire and lug thickness should be used. Many terminals will have separation washers to allow for more than one lug. Avoid stacking lugs on a terminal. Separate the lugs by placing them on opposite sides of a separation washer. If the terminal feeding the motor becomes loose it can overheat and burn.

After the wiring in the dust collector control box is complete, use the drilling template from the previous step to transfer the screw locations to the wall. Drill the holes to the appropriate size for whatever you're using to attach the detector box to the wall (plastic wall anchors, etc..)

Attach the detector control box to the wall.

Step 23: Secure the Motor Control Cable

Starting at the motor mount on the drum, use wire wraps to secure the motor control cable and drain wire. When you get near the dust collector frame, find a location to physically/electrically attach the drain wire to the frame. I did this by loosening a bolt that holds the cyclone to the frame.

Continue securing the motor control cable working towards the detector control box. I used wire wrap mounts attached to the wall with plastic wall anchors.

Once the motor control cable is plugged into the detector box, pull any slack on the motor control cable back to an inconspicuous location and wire wrap the loose coil. On my installation the slack is in back of the cyclone.

Turn on the dust collector. The green and blue LEDs should illuminate.

If you also are using my Audio Alert module, turn this on based on how you've configured it. My configuration is shown in the photo.

Step 24: Part Sources

12V 1.25A AC 110-220 power supply

DC-DC step down module

Orange flashing warning light

Motor Paddle Assy
60 RPM 6 volt, long shaft Mini Micro Metal Gear Motor

4.5m shielded 22 AWG 2-conductor with drain wire. It’s very important that this wire be shielded and have a drain wire. It’s being attached to your dust collector bin that generally is a static electricity source. Brand I used: Carol Cable Co: C2514.21.10. I don’t have a source other than eBay. I have a roll of this that I’ll never use up. If you need some, message me, just pay for postage (to US residents only.)

For all of the parts, bare board, assembled and tested board, motor, hardware, etc.. Message me if you live in the US and would like to acquire these parts from me.

As noted in the introduction, the board is shared on PCBWay.

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