EXT Cartridge Module

  1. Linear motor: the kind of vibrator installed in iPhone and some Android. Rich frequency response.

Do you mean “Linear Resonant Actuators” ? the “haptic enging like” thing? :thinking:

Ha, yes, me noob. Not the threaded rod linear motor kind.


The rtc chip is DS1307+, which can operate with minimum peripheral components. You’ll need to do a small board to host the chip and its peripherals, so that it becomes something like an adafruit module, and then interface with the core.

Note that ds1307 only works with 5v logic, so I additionally use a TXS0102 to do the conversion, which again requires its own peripherals.

So I’d recommend an off-shelf adafruit module (make sure to get 3.3v version, don’t risk your core board)

A someone who doesn’t have the skill to design it the one cartridge I would really need is one with USB inside, that’s big enough to contain a USB stick shaped device. This way I can easily make cartridges with specific jobs by shucking usb devices and putting them in there.

Yes people will likely make purpose built boards that do the job better, but this would be a good jumping off point.

That and a printer cartridge, just because it gives the Devterm it’s personality.


That’s a good point you’re making.

I already started on a breakout adapter, and a USB adapter is the next logical step before pursuing lofty goals. Hardware identification is still not set in stone for instance, and this doesn’t need it. Nothing fancy, just three USB ports internally, nothing more. Could be half a day’s worth of modeling and routing, extremely cheap to make.

A functional printer would be nice to have as well, but I need ideas on how to get the shape right.
I only arrive at the conclusion I did several posts ago, but I feel like it can be done better.
It could be tuned it so that the stock paper holder doesn’t flop around, overall beefier design.
I’m all ears about that one if anyone got an idea.

Yeah that looks good to me. If this gets to the stage where it’s ready for release I’ll happily take some of those, even if it comes as a kit. I can’t design but I can SMT solder.

I don’t know how to solve the paper cassette problem without designing a different paper cassette, aside from modelling it off the protective cap that came with the original, as that seems to fit fairly tightly.


The mechanical model fits 3 of these standard flash drives, but can be tweaked for whatever else.

I’m ordering PCBs after I’m done redoing the printer cartridge reviewing the latest revision of the EXT, so I can offset the shipping costs a bit.
After that I’ll be happy to compile some kits for anyone who wants them.

Regarding the printer again, I’ll try to redesign it from the ground up.
Maybe I’ll get inspired by looking at calculators.

Edit: How about this, a printer sidecar?

Instead of being awkwardly long, how about being awkwardly wide? :grin:
It’s got all the stability is should, there’s all the space needed and some extra (numpad, anyone?) plus that knob thing comes in handy to affix that unit.

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make this printer module usb-driven with a micro controller, and the printer cart can be composed with the usb cart… plus you can always detach it and use it on another computer


make this printer module usb-driven with a micro controller

Good idea! Tough I’m a teensy fanboy, I’ll look into a suitable STM32 for cost reasons.

and the printer cart can be composed with the usb cart…

Wouldn’t it be more powerful tough to be able to have a custom cart that’s not USB and in addition a printer?
Like a sensor one, then you can plot the data right out.

The USB can come from one of the covered ports on the side.
Then I can reuse my tried hub layout to replace the covered two USB ports.

From the technical side, a ttyUSB should be provided that works with the stock DevTerm system.

yeah, a lot of possibilities here. could be even a custom cart chasis + a plain usb cart pcb, but the form factor of the custom cart can allow mounting the printer in place.

Put me down for a kit, I can also help assemble them for others in the UK as well if there aren’t too many, I also can 3d print.

I will go with whatever you guys want to do for the printer option. I’m not so keen on the sidecar but could maybe do something standalone on a cable if we can’t do a cartridge

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Pencil cad, hard to fault a classic! Aren’t there off the self thermal usb printers in compact cases? A quick search shows a few but the form factor is not very nice.

@yatli had a genius idea regarding cheap hardware identification.
Please correct me if I got it wrong of course.

It involves a simple shift register, the two pins X1 and X2, and a pull down resistor.


ROUTE_EN as an input is pulled low by a 10k resistor on inserting the cart, this latches the 74HC165, then
ROUTE_EN switches to output and is driven high. In this period the shift register is read.
After reading, ROUTE_EN reverts back as an input and the resistor once again pulls low until the cart is removed.

Read out is 7 bits of identification and one “more” bit.
If the M bit is high, that means that more data for more information about the cartridge:

  • more identification bits following
  • flag if an I2C EEPROM with data is present
  • etc

Meanwhile regarding the printer, I’m picking up the cartridge idea up again. I’s a perfect test for the system.
I’m sure now after playing around a bit that the paper carriage can be stable.Still doesn’t change that’s gonna be a long one, dimensionally.

So these 4 cartridges it will be for the first batch:

  • USB: finished
  • thermal printer: schematic done, routing 50%
  • camera: schematic done, routing to do
  • breakout adapter: finished

If I remember correctly, 74HC165 has a SER input pin that shifts into the data bit, so that multiple can be chained together:

-----------------------  -----------------------
D1 D1 D1 D1 D1 D1 D1 D1  D2 D2 D2 D2 D2 D2 D2 D2
-----------------------  -----------------------
                                              ^--read one bit from 2nd 74HC165
| shift one
-----------------------  -----------------------
   D1 D1 D1 D1 D1 D1 D1  D1 D2 D2 D2 D2 D2 D2 D2
-----------------------  -----------------------
                                              ^--read one bit from 2nd 74HC165
| ... shift 7 more times

-----------------------  -----------------------
                         D1 D1 D1 D1 D1 D1 D1 D1
-----------------------  -----------------------
                                              ^--2nd 74HC165 starts outputting content of 1st

Hold on, what about this:

(Not sure if the PCB factory is happy about it!)
(PCB factory says it’s fine for a small batch)

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Would it be possible to create a cartridge with ethernet and rs232? I haven’t purchased a DevTerm yet, but adding that functionality would be awesome. I would use it on my job as a network engineer. I realize i can use usb to add these things, but then you have to carry multiple adapters.


Already onto that. Single 10/100/1000 Ethernet and RS232.
Shame that dual Ethernet does not fit, but would be possible if the D-Sub is dropped.
Maybe I can base an intercepter cartridge off this one.

Expect a release when I’m done with the initial batch of cartridges.
Regarding the first batch, the following are currently produced:

  • Camera
  • Breakout
  • USB
  • Printer

So so so cool!
A Solar cell on top would be cool!

It would take ages to charge (if at all) but it definitely fits the vibe.

Yeah, that’s part of why I bought my devterm, small device to configure switches with serial or ssh. For now I bought a knockoff usb to Cisco rj45 serial device, then made an rj45 to db9 for other switches. And add a simple 10/100 usb adapter for ethernet (usb2 so no need for a gigabit adapter).

Using minicom for my serial terminal.

Regarding the ethernet serial module, could you fit 3 rj45? You could configure one of them to serial, many newer switches are coming with rj45 for the serial port. That said most also have a usb port for serial so maybe the db9 doesn’t matter too much.