Basic Hacker MultiBench

To reduce the desktop footprint I have added an option for an external power brick.  It is equivalent to the internal one i.e. 24V 5A so requires a mod to the rear to take a 5.5mm x 2.5mm barrel jack panel mount socket.  This also avoids anyone messing with mains voltage.  

I did not want this to stick straight out the rear stopping it from being pushed to the back of my desk so I have angled it so that the plug is mostly enclosed and the wire drops down from the rear.  Makes it a neater job.

I have updated the OpenSCAD file to include this, added an stl file for it and added some photos to show the internal and external change.

Been busy on other projects so only posting this now.  Any questions just add to the discussion

A few comments on the voltmeters and ammeters. First on the housing.  These all come with shells that click into a hole quite easily.  This would have made the 3D model simpler but they need more space and I wanted a nice line and symmetry below the DPS3005 so the best way was to create the mounting in the 3D model. In my case the bare voltmeter/ammeter board are a friction fit but you can use a little hot glue if they are not sitting in correctly.

Second thing is accuracy.  These are cheap voltmeter/ammeters.  In most cases we are just not looking for precision, just a rough value, most of these are accurate to about 0.1V and some can be tweaked with a small potentiometer on the board so look out for that if it is important.  Generally it is fine and I don't have to pull out a proper multi-meter.

When connecting to the ammeter it seems strange to connect the thick red wire to the black binding post but since this is the current coming from the load and the thick black wire is connected to 0V it makes sense.  Just follow connections from the load.

Uploaded pictures of the PSU back case with wiring.  Using fork type crimps bent to fit the case to allow the safety cover to click in place while still sliding back into the case.

Mains live wire passes through a 3A switch before connecting to the PSU live mains terminal to allow for local isolation.  The 12V line connects via an inline fuse before being soldered onto the female XT60 connector. 

Added a little strain relief on the mains cable with a tie wrap to prevent the cable being pulled out.  I don't intend to move this much so should not get much stress.

Note: do not work with mains electricity unless you are confident working with this.  Use a 24V 5A power brick and swap to a barrel jack rated at >5A.

There are 6 dc - dc buck convertors in this project, while not as inefficient as linear regulators they can still get toasty.  If the supplies are only getting light use the there is probably no need for a fan, just make sure that you have the base raised (using stick on rubber feet) as there are some holes underneath for air flow.

If you are ramping up the amps then a bit of assisted airflow is worth considering.  I have included mounting holes for a 60mm x 60mm x 15mm fan on the inside of the main unit.  I have a few of these on order from AliExpress to try it out but not needed it yet.

If you have the full unit with the power supply then the fan will pull air though the main unit and push it through the PSU so the one fan should do the job.

The LM2596S Dual USB Power Supply Module is fairly cheap (~$1.5) and can churn out 3A (2A + 1A).  If they are being pushed above 2A adding a small heat sink would be recommended (only cost a few cents but I had a couple spare from A4988 driver boards)

Wiring diagrams are now shown in png images.  This covers meters, binding posts, 12V/24V selector switch, barrel socket and DPS3005.  Buck convector wiring for DSO150 has been added but best to follow the JTech instructions to build the oscilloscope.

Note, when you are building this oscilloscope it is very easy to get it wrong if you not follow the pictures on the JTech guide.  Particularly soldering the encoder switch to the correct side of the additional board.

Diagram for Voltmeter and Continuity Tester Wiring has been added.  Programming can be done with continuity.ino file.

The continuity tester uses an AtTiny85 Digispark board, one resistor (close to 50ohm) and one active buzzer.  Also only needs one line of actual code (excluding pin settings) and is a nice starting project for using the AtTiny with total project cost about $2 (+postage).

Files are:

• AtTiny85 Continuity Build.png
• Continuity.ino

Added 3D stl files and OpenSCAD file for customisation.  Also available on thingiverse: https://www.thingiverse.com/thing:4988627