Introduction: Portable Arduino Workbench Part 2
I'd already made a couple of these boxes described in part 1, and if a box to carry things around and keep a project together is all that's required then they will work fine. I wanted to be able to keep the whole project self contained and move it around where I wanted, work on it whenever, and be able to just close it up and move on.
After I built this part I found that the space for including all the electronics I wanted to put in just didn't fit in this design so created a part2B which I recommend you read as well as this if making something similar. The first version and second version are shown above. The big difference to take into account are the PSU panels and display panels which are the same size but cut differently.
Various offcuts of 9mm plywood from the previous project, mostly 20cm wide.
1 x XLR male chassis socket, rated for 10-16A dc
1 x IEC mains socket with illuminated switch and fuse
1 x 12V switch mode power supply
1 x DPDT centre off switch
1 x SPST switch with LED
1 x Red banana socket rated to at least 10A
1 x Black banana socket rated to at least 10A
Short colour coded leads with spade connectors, see text
Step 1: Basic PSU Wiring
The basic wiring is to provide a nominal switched 12V at a pair of banana sockets in the base section of the box.
There are two inlets on the box. A standard IEC socket, fused and with an illuminated switch provides a local mains connection. I've used my own separate mains PSU for many years and not having an illuminated switch has been a frequent irritation, so I appreciate adding one now. The other inlet is an XLR 3pin male socket, rated for 16A, and which will be used with cable to connect it to a 12V battery system. This will be either in my cabin, adapted for solar power, or in my RV when away.
The mains inlet feeds a 12V switched mode power supply setup for the local mains voltage and providing up to 8.5A, and particularly sized to fit into the box. Larger PSUs were available for not much more money but they both wouldn't fit and also are not necessary in just a small workbench environment.
Both the battery and PSU are connected to a common negative rail and individually to two poles of a changeover switch with a centre off position so that power can be selected from either source or isolated completely. Rocker switches were chosen for this roll so as to not interfere with the project wiring when the box lid was closed.
The positive supply from the changeover switch is routed to the output via an illuminated isolation switch, again to provide indication that power is on. Using lit switches makes it easy for me to see what is happening.
Finally, the output from the PSU component is output via two 4mm banana sockets, nominally delivering 12V. The purpose of these is to either provide 12v directly to the projects assembled in the lid or to the additional stepdown PSUs and electronics in the lid, described in the next part.
Step 2: Fitting Inlets
The measurements for the inlet cut outs are shown in the diagram. The XLR socket is fairly standard but IEC sockets can vary so while these are a guide, do check the measurements of the actual socket you have.
The XLR inlet was cut with a 21mm hole saw, running it gently so as not to tear the wood as it came out the other side. The XLR socket I used had three location lugs which required a small amount of rasping of the wood to cut three notches, shown in the picture, but the one you use may not.
The rectangular hole for the IEC socket was marked out on the box first, then four 10mm holes drilled close to the inside corners of the shape, without crossing the lines, to give access to a jigsaw blade, used to cut the final rectangle out. From the pictures you can see I wasn't perfect at that final task but the flange on the socket covers up small mistakes like that.
Finally, both sockets were fitted in their cut outs, small pilot holes drilled for screws in the locating holes and the sockets fixed in place with screws.
Step 3: PSU Location and Boxing In
The mains PSU will be located as shown in the picture, and a box placed round it for safety and to prevent loose components interfering with its operation.
The plywood layout for the box is shown, a lid and a side piece, together with three small strips of wood to help fix the lid and side in place.
One strip of wood is glued to the side of the box so that its top edge is 82mm above the base its whole length.
One strip of wood is glued to the base so that its edge is 140mm across the base.
For both these strips its a useful idea to draw a line across the box with a sharp pencil using the box edge and box lid as guides.
Finally, glue the last strip to the long edge of the edge piece. This will be used to screw the lid to afterwards.
If you don't have clamps then the strips will have to be fitted one at a time and the box placed on its side while the glue sets.
I have considered fitting a fan to the PSU box and will do so if heat proves to be a problem.
Step 4: PSU and Panel Cutting
The lid of the PSU was cut out as per the picture, the banana sockets and switches added afterwards to test size. The other panels in the picture are for making the console part of the box in the lid so if you aren't going any further won't be needed. The two small rectangles of wood were used to brace the PSU box when it was glued in place, as per the picture of the PSU internal side wall.
The intention is to put the console into the lid, driven by an Arduino Mega. As this project will be in a state of flux for months to come, I've cut a hole in the side of the box lid to enable the Arduino to be programmed without having to de-install it. The two triangular pieces of wood support the console panel at a 45 degree angle, and one of them is cut out to accommodate the Arduino board fitting against the case.
The console front is 230mm by 127mm and is cut at the edges to 45 degrees to fit neatly to the box. I did this on my band saw but a power sander or plane could be used with frequent measurements of the angle when cutting..
Step 5: Painting and PSU Assembly
The bare cut plywood was already generating a lot of splinters and I had originally intended to varnish the box, but what I had was green paint and that's the reason it's the way it is.
All the parts were assembled in the PSU compartment and connected as per the diagram. In this first version I've used clips but more reliable connections might be made by soldering them. The 12V power supply was screwed to the inside of the box with 8mm long screws.
The mains PSU has insulated connections but ideally should have an full insulated cover fitted, which I will do when I can find a source for this size of socket.
Step 6: Console Cut Out
This is only necessary if going further with the box.
The console panel was cut out to accommodate the various controls as per the labelled picture. The photographs show the first console where the power sockets were opposite each other on base and lid. This has an issue depending on the plugs used which stops the lid closing. The new console layout drawings swap the console sockets with one of the switches so that when the lid is closed, they don't conflict.
The two banana sockets are the power in connections from the PSU in the base.
The switches are illuminated on/off for 12V, 5V and USB sockets, not fitted yet. Next to them are the power pins and sockets. Each power supply has a row of dupont sockets above a double row of pins in a header socket. This is probably far more than necessary but was easy to provide and doesn't take up much space. How they are soldered is shown in the rear view picture.
The idea behind using the PCB header sockets in the role, was to facilitate the use of an IDE plug and multiple wires to make an easy connection to the sockets with flying leads so I didn't have to be able to see the sockets well and the leads could be colour coded.
Next to the power sockets is the main display, 3.5" TFT, which will be driven by the Arduino, to display voltages, currents, resistance and digital pin status. It will also include a serial monitor and I2C connection.
Below this are the input connections, again a row of dupont sockets above a double row of pins. The first eight are digital input pins, the next four are basic voltage measurements, the next six are current/voltage measurement connections, and finally serial input and I2C connections. One of the consoles objectives is to be able to support expansion using I2C connected external circuits.
The other pictures show the box with painted console panel in place, an Arduino board in place in the lid with external connections, and a trial layout of the buck/boost PSU modules.
3.3V sockets haven't been included in the design yet but I will wait to see how much they are needed in regular usage.
Step 7: Final Mock-up and Resistance Measurements
The pictures show the final mock-up of the console part of the box before wiring, and incudes the USB sockets and resistance meter connections.
The purpose of the resistance meter in this case is to provide a quick check on the value of a resistor which I'm unable to see. The connections are made using two small springs which have been cut down and bent to allow them to be attached to the console front, using a bolt and solder tag, for easy access. To check a component, it has only to be held across the two springs and the value will be displayed.
All the circuits and assembly for the console, as well as the Arduino code, are in the third part, but this concludes the PSU and wooden construction of the project. The last picture isn't working yet, but is where this is headed.