I wanted to make an industrial control panel to control all the inputs/outputs of the system, with a bit of room inside to expand the functionality in the future. My idea is to use an HMI (industrial touch screen) to create the user interface, and from there use a PLC to control a bank of relays to switch on and off outlets for appliances. Since most of the devices use mains power, it seems like a good idea to create a sort of “power distribution unit” to control everything.
Since none of the devices are necessarily power hungry, I can run them off of one 15 amp outlet with a ‘kill-a-watt’ plug to check my average current draw and calculate how much power it takes me to produce fruit (yay stats!)
Power Distribution (PDU)
While I prepare the backplane for the control panel itself, I can start working on the power distribution. I have to consider how many outputs my PLC has, and how many I can afford to dedicate to controlling outlets.
Presently, the PLC has 8 outputs, one of which is analog. I made a list of what I would want these to control.
– Lights (120v Digital)
– Light Brightness (0-10v Analog)
– Fan (120v Digital)
– Fan Speed (24v High Speed PWM)
– Pump (120v Digital)
– Misters (24v Digital)
– Aux #1 (120v Digital)
– Aux #2 (120v Digital)
I determined I would need 6 relays, 5 of which would be controlling mains outlets and the other could be a faster solid state relay for turning on and off a solenoid for misting. The other 2 outputs — The PWM and analog signals — would not need relays and feed directly into their own circuits.
I daisy-chained the live wires on all the outlets, and wired the neutral wires individually to each relay. Functionally, I would be using the PLC to act as a low-side switch for each outlet.
DIN Backplane
I cut a stainless steel backplane to mount the DIN rails along with all the components, and began to wire all the relays to the PLC. It would have to be large enough to fit the PLC, the relays, a 24v power supply, a breaker, and several terminal blocks to ease wiring all the different components.
I added a couple of holes to add some wire channels in the future, but placing any in the spaces above or below the DIN rails would be way too tight. I’ll have to explore other methods of hiding the cables or making my wiring more tidy. That said, everything here is functional. Placing the AC wiring next to the 24v outputs of the PLC is certainly not best practice, but the noise generated by it seems to be so small it doesn’t have any significant effect on my signals. Sometime in the future I may probe out the PWM signal (which is probably the most sensitive one) to determine if there is actually any noticeable effect at all.
The Enclosure
I ordered a polycarbonate case to fit everything inside, and started to make the necessary customizations to fit all the connections necessary.
I would primarily need a large rectangular hole in the front for the HMI, as well as a hole in the bottom for conduit to supply the PDU. I would also need several holes on the side, for the main power cable and for each I/O that isn’t going through the PDU.
Assembly and Mounting
I put together all the components and mounted the Enclosure as well as the PDU onto the wall. Since this particular wall is a shear wall, I had a lot more flexibility on choosing exactly where both these two boxes would go. I mounted the backplane inside of the enclosure, made sure all the mains lines were in conduit, and connected each field device to their respective I/O or relay. I also mounted the HMI onto the hinged portion, and braided the power lines going to it.
I also screwed the LED driver to the wall, and put the kill-a-watt monitor on the outlet I’ll be drawing from. This way, I can track exactly how much electricity this system uses and correlate it to the yields I get once everything grows.
I designed a very rudimentary HMI program to control all the variables (though it isn’t very pretty), and tested all the devices to make sure everything works. There are a couple of exposed 24v lines on the side, due to an uninsulated perfboard circuit (from the previous post) as well as the screws on the thermometer transmitter.
I still have many things on my to-do list before I can call this control panel truly complete, and I’ll list them here so that I don’t get too lazy and leave things half done.
- Cable management (Strain reliefs/glands, cutting things to size etc)
- Enclosures for all 24v circuits and transmitters
- Fancier HMI vector graphics
- Better connectors
I’ll leave these finishing touches for a part 2 post, as I might take a while to complete them. I don’t want to start my seeds later than I already am, so I intend on using this system as soon as possible. The aesthetics of it may still be unfinished, but it is performing its functions well enough. After all, I’ll have plenty of time to work on graphics as the seedlings begin sprouting.