In this part of the dust extraction build I will show the current sensor. This sensor measures the current that the tool draws and gives a signal to a central unit once it is higher than a set value. In order to leave the vacuum cleaner on during the machine spinning down a settable timer is added. Also I added a start stop circuit, witch can be used to manually start/stop the valve and vacuum. This can be handy to clean the work table. These buttons are not placed on all sensor units.
This unit consists of 2 parts.
Part 1: the current sensor:
A current transformer (ASM-010) is placed around the live wire.
The output of this transformer is send trough a 50R resistance. This converts the output current of the clamp to a voltage. This voltage is then amplified and compared against a level set by the potmeter. After this a 555 timer is added to keep the suction active while the machines motor spins down.
Part 2: on / off buttons:
This part works with a set reset flipflop. This has 2 buttons connected to manually start / stop the dust extractor.
Total:
The output of the 2 parts are coupled together with 2 diodes to a transistor that pulls the interface line to the controller low when it wants to turn on the dust extractor.
The PCB I designed for this project:
In order to keep the potmeters in place I added a small 3d printed bracket.
Build in the enclosure:
Links to previous parts of this build:
Dust extraction – Part 1: Valves
The next part of this project will be the central unit.
Dutch 
