In this part of the dust extraction build I will show the central unit. This unit receives the signals from the current sensor boxes and uses this information to switch the valves and the vacuum cleaner.
Some time ago I designed a board with a pic processor that has robust in and outputs. These have protections similar to a PLC has.
To drive the valves a lot of current is required, more than this board can drive, also more outputs are needed. Therefore I bought a 16 channel relay board.
This relay board needs 16 signals to drive the relays, unfortunately the board I use only has 8 outputs, of which 1 is already taken by the vacuum cleaner. Therefore I designed a board around 2x 74HCT595 IC’s to drive the relay board. To make the board also useful for other applications I added ULN2803 drivers to each output, however they are not used in this project.
There are optocouplers on the relay board in the drive path of the relays. They invert the signals. I do not want this, so I removed these and replaced them with 0 Ohm resistors.
The inputs I have on the controller board are made for PNP sensors, however the sensors have a NPN on the output. This I fixed by putting pullup resistors on the inputs. However this makes the signals come in the microcontroller inverted, but this is easy fixed in the firmware.
All boards mounted / wired to contact strips:
Next to the dust extraction controller I also build the power supply + power distribution strips for the LED strips. To provide music in the workshop I also fitted an audio amplifier in this enclosure.
Links to previous parts of this build:
Dust extraction – Part 1: Valves
Dust extraction – Part 2: Current sensor
The next part of this project will be the solid state relay.
Dutch 
