This is an external disk drive in what is probably an insulation tester from the 1930s.
There was little left internally but the wiring and insulation suggests a date before WW2.
The meter now indicates the amount of USB traffic.
It does look rather fine and always impresses when I carry it into an office.
I hope this Instructable inspires you to create your own drive case. It also shows how to make a USB meter.
You'll need the usual handtools and a soldering iron; plus a few electronic components to make the USB meter.
Length 177mm; Width 112mm; Height 163mm.
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Step 1: The Box
The box had once contained accumulators to power the tester and had a socket on each side, presumably for the device being tested.
The handle on top came from a violin case I found sticking out of a dustbin.
The hooks at the bottom open the compartment for the accumulator. The compartment is a useful place to store the USB cable.
Step 2: The Meter
There is a War Department arrow on the meter but that's probably just where the meter came from. The rest of the box looks like it's non-military. It's been professionally manufactured: the woodwork is clearly not hand-made.
On the right, you can just see the stripboard with the circuit for the USB meter.
The meter shows the amount of USB traffic. It's surprising how little time the USB is active even when you're copying large files.
Step 3: The Disk Drive
The disk drive is a 1Tb Buffalo Ministation. It's a nice small drive at 114mm x 77mm x 14mm and is powered via the USB cable.
You would think there would be a lot of room but the drive only just fits.
It is padded with soft foam (not shown) so it doesn't rattle around.
The disk drive has a mini USB socket but I converted that to a USB-B connector so I could use a standard USB A-to-B cable. A short cable connects a mini USB plug to a USB-B socket.
Step 4: The Electronics
The meter reacts to the rate of data transfer along a USB cable. The circuit certainly works with a disk drive plugged into a USB 1.0 or 2.0 socket. I haven't tried it with, say, a memory stick.
The first schematic (above) shows the circuit I built. The LM392 contains a comparator and an op-amp. The comparator looks for when the USB D+ line exceeds the D- line. The op-amp drives the meter. R1 is a pullup for the output of the comparator (which is open-drain).
The meter is connected to PL1,PL2. The old meter in the current design had a FSD of maybe 10mA. A resistor may be needed in-line with a different meter.
I'm not sure why R4 is needed. When the USB is inactive, both D- and D+ seem to go to 0V - maybe they're tristate - and the comparator starts to oscillate. The 100k pullup is just enough to stop the oscillation.
I used stripboard for the LM392 pcb and tripad board to hold a USB B receptacle. The connectors act as a convertor from a USB mini plug to a USB B receptacle.
(Layout show from component side. In the prototype, R4 is on the back side.)
The standard USB wire colours are:
- 5V Red
- D- White
- D+ Green
- 0V Black
Of course, you don't need both an op-amp and a comparator. I suspect a better circuit would be like the second schematic (above). But the circuit I built works fine.
The circuit works with a USB 3 connection that's operating in USB 2.0 mode (i.e. a USB 2 device plugged into a USB 3 socket). I haven't tried it with a USB 3 device.
As the data transfer rate of USB 3 is faster, it may show a very small meter deflection. It's going to depend on the meter you're using.
If you need to stretch the USB pulses to get enough meter deflection, you could use the comparator of the LM392 to detect the USB data and use the op-amp as a monostable to stretch the pulses which drive the meter.