Portable Arduino Workbench Part 2B

This is both a continuation and a change in direction from the previous two instructables. I built the main carcass of the box and that worked ok, I added the psu and that worked ok, but then I tried to put the circuits I'd built into the remainder of the box and they didn't fit. In fact if I made them fit, then there wasn't room to include a project. The compromise I have made is to move all the switches and power supplies into the main box out of the lid, giving more room for the wiring.

The whole closes up into a box which can be easily moved from place to place or put away for storage. Not shown here, but the front of the lid contains another separate board to which breadboards are attached and can be fixed with velcro. I'll organise pictures of this asap.

For this revised stage only

9mm plywood

14 x 20cm, 13 x 23cm, 2 x 23cm

40pin male header

4 x illuminated rocker switches

1 x DPDT centre off rocker switch (can be just DPDT)

USB Hub 4-way with switched supplies. A common model is shown in the pictures

USB type B panel mount socket

2 x buck/boost voltage down convertors, adjusted to 5V

1 x buck/boost voltage up/down convertor, adjusted to 12V

1 x buck/boost dual rail voltage up/down convertor, adjusted to 12V

Various matrix board bits, I've used offcuts and rejects instead of new perfect board

Lots of multistrand wire, rated for 3A or more.

Spade connectors

Negative voltage generator

555 timer IC

Resistors 4k8 and 33K 1/4watt

Polyester capacitors 22n, 10n

Electrolytic capacitors 33u and 220u (30V plus rating)

2 x 1N4001 diodes, but any small rectifier diodes will do.

The main power supply is built into bottom half of the box and is made up of commercial off the shelf switching units, connected together with a set of switches and supplying power to the electronics in the lid of the box via a 40pin ribbon cable and connectors. The power is provided by either a mains inlet and 12V dc switching psu, or via an XLR socket intended to receive power from a 12V battery supply, if in use in an RV but could be a battery carried in the box itself. Power from either of these is selected via a three way switch, mains, battery or centre off position.

The power is switched by an illuminated rocker switch to indicate power on. The main power on provides power to the other switches and to a 12V buck-boost supply providing power to the lid electronics. This also feeds to a simple negative voltage generator for the analogue components in the display.

A 5V buck-boost module is supplied by an illuminated rocker switch and provides 5V for use by constructed circuits in the lid and is routed via the ribbon cable.

A +/- 12V buck-boost module is supplied by an illuminated rocker switch and provide both a +12V and -12V supplies for use by analogue circuits and is routed via the ribbon cable.

A fourth buck-boost module is fed from the final switch to provide power to the USB hub. The USB 2.0 hub is a low cost item which provides four power switched sockets as well as the logic to run as a hub. More on this later.

To fit the new power supply layout, new panels needed to be cut, the layout of these is in the pdfs, as well as an extension to the side of the lid to give more space to the wires behind.

The power supply in the original was via banana plugs and sockets, but with this one having multiple power supplies, the connection between lid and base is via a 40 way ribbon cable. The socket is is soldered to a piece of matrix board which is pushed through the hole made for it and screwed in place. The sockets are keyed so when fitting them to the boards they need to be lined up to ensure the the ribbon cable used fits neatly between them and isn't reversed. I've used a 20cm ribbon cable which at the measurements used just folds up nicely as the lid is closed.

To build the PSU circuits, they were assembled on the panel and screwed in place, either with spacers or pcb clips. Both were printed on a 3D printer in this case but that isn't necessary, just that the boards are secured. I've added the .stl files in case anyone wants to make them quickly.

All wiring on the panel was soldered, except the connections to the main base PSU connections to enable the lid to be easily removed and replaced.

The resistance meter and volt meter circuits use buffer amplifiers which need both positive and negative supplies. The positive supply is obtained from an up/down buck convertor which supplies a steady +12V independently of the external source. This feeds the lid circuits and the negative voltage generator. Originally this was included on the same matrix board as the other electronics but has been cut off to be placed in the base. The circuit for this is shown and is a common 555 timer circuit for this purpose. It only supplies enough current to run the buffer amplifiers and isn't needed for anything else.

The original USB supply was a pair of sockets in the lid fed from a separate 5V supply and providing only power. Because I wanted this to be as portable as possible, I decided to put a USB hub in the build, fixed in the base, and with a modified power supply fed from a 5V buck converter. This hub can also be used with the programming computer as a USB hub simplifying connections.

The base of the USB hub was prized off and the connections shown soldered on to the board. The lead was replaced by a USB type B socket with only the signal and 0V connections soldered to the USB hub circuit board. No traces were cut in this modification, just the 5V supply is enhanced by thicker wire to the USB power switches in the hub and an extra wire taking the power directly to the pins on the sockets, bypassing the circuit board traces.

This does mean that the supply is now limited to 3A instead of the usual 500mA, but will power a Raspberry Pi.

To fit to the top of the PSU panel, the base of the hub was screwed down with a hole placed for the wires to pass through and the hub reassembled on top.

The completed PSU panel is shown in the picture.

The electronics and Arduino code is covered in the last part but for construction purposes is partly shown here to show where things will go. They could be constructed completely separately and never used in a project box like this.

The power for the display panel is connected via the 40 way header socket which has been lined up with the socket in the base to ensure the ribbon cable folds neatly.

Below it is a red reset button for the Arduino, its an easy addition and as the whole is expected to be an ongoing project may be required from time to time.

In the centre are the power supplies, from the top that is +12V, -12V, +5V and 0V

Below the display are the various inputs to the circuits, digital input, voltage input, current, serial and I2C pins

Above the display are the spring connectors for the resistance measurement.

The display has a simple bezel put around it, currently white but will be changed if I have the plastic to make one.

Also shown in the pictures are two wooden shims and a spacing piece put on the lid. The whole of the panel had to be moved forward to accommodate the wiring behind. The cutting directions for these are in the attached PDFs.

Here are the stl files for anyone who wants to make, or have made, the various stand-offs, PCB mounts and the bezel.