Hello, my name is Doug and I'm a gadgetaholic, and the gadget in the 2nd picture below really tickles my fancy.
I have not been blogging much this year, but with all the lockdowns in place, I think it is important to stay connected, stay positive, communicate, find ways to relieve the stress, distract ourselves from obsessing over problems we can't solve, find ways to have some fun, maybe even find time to indulge in a few harmless vices.
This blog is about a quest I have been on for several decades. It starts back when I was a student …. my best summer job was in an electronics lab where I had all sorts of miscellaneous tasks that taught me a lot that I didn't know, and a lot that I would never learn in my engineering courses. One of the things I did was simply sorting components, which seems pretty menial, but I actually learned a lot from doing it, and it is why I can read colour code values at a glance without thinking or calculating. That lab had a General Radio LCR meter that I found intriguing and extremely useful for several of the tasks I had.
Ever since then I have had a disproportionately high desire (relative to actual need) to own a nice RLC meter, but they always seemed too expensive for me to justify purchasing. I still don't have a dedicated one like the GenRad, although I have collected a bunch of meters that more or less cover the functionality of an RLC meter.
My latest instrument is a bit more of a novelty than a serious meter, but nonetheless it is very cool because it is deceptively smart and very versatile. I like having it more because it is cool than any high performance capability.
Here it is – the T7 Multitester. These instruments are quite fragile, both mechanically and electrically. This blog explains a few things I have done to improve the device and fix some of the issues.
- The first issue is the USB charging port is recessed behind a thick plastic panel which barely allows the USB charging connector to make contact. It can make contact, but the connector falls out if you just look at it sideways. I designed a 3D printed replacement panel with a pocket around the USB port that allows the connector overmold to go into the panel far enough to properly seat the connector.
- The second issue is that the device doesn't really turn off, it just goes into a sleep mode, so it continues to drain the battery when it is off.
- A third issue that I've seen others have, is that the internal MCU can crash and there is no way to reset it.
Both of these issues can be solved by adding a power switch that disconnects the battery when the instrument is not in use. There is lots of room to add a switch to the top panel, so I designed a 2 part panel that locks the switch in place without any fasteners.
- A fourth issue I discovered after taking the case apart is that the bosses for mounting the PCB do not extend all the way to the PCB, so if the screws are tightened, even minimally, the PCB will have to bend. I solved this by 3D printing some stand-off spacers and dowels.
In all, I used eleven 3D printed parts, a slide switch and some hookup wire to eliminate all the issues outlined above. However the parts are small so they print quickly.
It still isn't a robust, high-accuracy instrument, but like I mentioned, something about it really tickles my fancy and I like it even more now that I have made some improvements.
Here are a few more examples of the T7 in action. This isn't any kind of exhaustive road test, I am not even showing all the functions it has, but I wanted to provide a little feel for how its operation compares to regular DVMs.
I am pretty impressed that it can automagically figure out what random components and devices are plugged into it.
However, the quest continues to obtain a "real" RLC meter....
If you try these upgrades for your T7 using the enclosed 3D print files, you will need a standard slide switch with a body size (LxWxH) of 12.7 mm x 6.6 mm x 6.3 mm:
I think these would work:
E-Switch 500SSP1S2M2QEA 500SSP1S2M2QEA
Carling Tech 4M1-SSP1
The attached zip file includes .stl files for the 3D printed parts:
- Spacer.stl - spacers for the PCB
- DowelPin.stl - pins to hold the PCB to the spacers
- SwitchPanel - panel to hold the slide switch
- SwitchBezel.stl - exterior bezel for the slide switch panel
A multitester user manual can be found here:
Here is a schematic I found online here:
The code also seems to available online.
I did a segment on a similar device earlier:
Sixth Sense - Interfaces - GraffitiBot blog 4