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.

Supplies

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.

Step 1: Main Box PSU

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.

Step 2: New Base and Lid Panels

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.

Step 3: Negative Voltage Generator

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.

Step 4: USB Hub

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.

Step 5: Lid Panels and View of Electronics

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.

Step 6: Stl Files for Mounts and Bezels

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

Comments

[tekyinblack]

Hi,
I did make another version based on this, but haven’t finished writing it up. The ina3221 had to be modified but since then I’ve found another version of the board which uses the ina3221 but in a discrete measurement format the same as my modified version. This works much better. Otherwise the basic analog inputs on the Arduino work ok with voltage divider resistors, not ultra precise but good enough for the basic usage I have for it. Don’t have a clear source for these boards but they are on black pubs rather than the purple ones I modified.

[charliecat2015]

Hey there. Much respect for your project. I am in the planning stages of building a teensy 4.1 based development board. i have a dual rail variable linear +-15vdc circuit built and want to put a touch screen or a nice screen anyway in the board so i'll have to do a layout. One part will be monitoring the voltage rails i have. i plan to have the dual linear rails and a third for adding dc offsets. i may use an active bms set up for the third to keep noise down. I'm wondering if the way you implemented the voltage monitoring with the off the shelf board was to your satisfaction? It looks like a project to be very proud of and exceeds my skills. The pursuit of knowledge is what got us into this hobby right and humility is a virtue I think. Youtube is dominated by CCP endorsements and it's lead to an overarching feeling of a "what can you do for me" attitude with the creators whom i have been channel members of for years and such. I have mental ilness but an unused engineering degree and a want to help people so im making these boards for the local makerspace that for some reason hate me for asking why no one met me when i dropped off 5k worth of stuff i saved up for and that soured them on me. It was a question made in ernest, humility with no agression but people dont like me because my ilness causes me to ramble. As you can see.

i plan to use 2 ten turn precision pots for the linear supply and a pot with similar knob for the third voltage. im going to add ziff connectors and pomona mini barrell jacks for the whole board. Mine will have an audio path similar to your's but im getting ahead of myself.

I'm wondering if you'd do anything differently with regards to voltage monitoring if you knew what you know now. I have not plans to monitor current except to have short circuit protections. this is my winter project. I spent a fortune on another one only to find out that all the motors and such I bought are not suitable in salt water. A fact not mentioned in the ali express ad and when asked at pos the quick buck attitude of the chinese culture led me to be lied to without recompense when i politely brought it up. I dont have it in me to file disputes so they pretty much walk all over me being they are on the other side of the planet. Sorry if this seems racially charged, it's not, i assure you. I'm a student of knowledge which has caused me to read alot about why I was getting ripped off all the time and warranties not honored properly and such. My friend sells on ali and amazon and amazon takes fifteen percent no matter the sale's outcome so I used Ali alot for jelly bean stuff. They sell so many fake op amps it's bananas, i've had the kit ones explode with less than a watt.


Whether you reply or not, much respect for your project and all the hardwork posting it. You're one in a million. If you are in canada or the us and want a free box of leds and other random components and some random gear just email me and reference this message. i'll ship ya some cool stuff for all your trouble. take care.