This post is about a strange thing that looks like someone 3D printed the moment a microwave had a brilliant idea....
Rod at The Future Was 8 bit told me to expect to expect a mysterious package, and one duly arrived.
Within were more mysterious packages.
One bag contained some mysterious wires.
The other a small blue box with a light bulb on the top, a panel meter and switch on the front, and two DC jack sockets, one on either side.
What on earth is it?
Blue box with a light on top? No, it can't be, can it?
I nervously flicked the switch.
It didn't explode.
Phew.
OK, so, it is not the cold fusion generator he has been secretly working on.
Maybe next time.
I found the answer on the back.
"Low Voltage DC Power Tester"
Ah, that would explain it.
Neat.
I plugged in a power supply cable (12V, centre positive) and it lit up.
Oh, it's one of those panel meter things.
So that is showing the off load voltage and no current flow.
I tried turning the switch to the left.
The bulb lit up, and the ammeter portion updated to show 0.35A. That's about 4.3W.
I presume that is a standard dual filament car bulb, so that is meant to be around 5W (and would be at the 13-14V a car normally runs at)
I clicked the switch the other way and lost my eyesight for a few minutes.
That is the other filament then, specified as 21W. I am seeing the voltage of my power supply drop a little, as would be expected, now 12.1V with 1.6A flowing, so 19.5W.
That's quite handy to see how your power supply does on and off load.
The output jack also allows you to plug in a load of your own, in this case, a small monitor.
The display refresh rates seem to confuse the camera sometimes, but to the eye it is bright and clear.
A handy little device.
I did wonder about having a look inside, but it appears to be sealed, with no visible way in, and writing on all the sides.
My curiosity has now been satisfied, as TFW8b has put up a build video (link at the end)
The construction is very clever, the way it all fits together into the 3D printed enclosure.
Thank you to TFW8b for these photos (and obviously for the tester itself).
Inside, the DC jacks are soldered to the body of the lamp socket. It is a little confusing, it is wired like a positive earth car, the body of the socket is positive.
The larger black and read plug is the ammeter connection, wired between the negatives of the input and outputs.
The red and yellow lead is power and input voltage for the meter (connected together).
The black wire on the right is the centre of the switch, it is centre off, with the two on positions connected to the other end of the bulb filaments.
Once everything is assembled, the meter pushes into the opening and closes the case.
All ready for use.
Rod supplied a sort of "physical schematic", but I worked most of it out from the photos above.
Hmmmm, I thought I had the copyright on the wooden desktop shots?
I wanted to draw a proper schematic, but it took quite a few goes to find an arrangement I was happy with.
This one was almost there, and is maybe clearer about the way the loads are attached across the output.
I think this one is overall clearer, so I will stick with that.
Just remember it is centre positive, the type used on pretty much everything apart from the ZX Spectrum, Commodore 16, guitar pedals and Minstrel and Mini PET kits.
You can use those, just remember to use leads with the polarity swapped when connecting the device.
Looks like Rod also made a green one. Nice.
Build Video
See the full build video below on the TFW8b.com you tubes.
Well, I say full, it's 15 minutes, apparently the world wasn't ready for the full 3 hours directors cut.
Adverts
You can find more goodies from the Future Was 8 bit at TFW8b.com, such as the Penultimate Cartridge, SD2PET, SD2IEC, divMMC etc. although not this tester.
Tindie
My Tindie store contains all sort of kits, test gear and upgrades for the ZX80, ZX81, Jupiter ACE, and Commodore PET.
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You can support me via Patreon, and get access to advance previews of blog posts, and progress updates on new projects like the Mini PET II and Mini VIC and other behind the scenes updates. This also includes access to my Patreon only Discord server for even more regular updates.
