I don’t know why I hadn’t seen or thought of this before 
Testing a fuse using your smartphone:
Has anyone else got any clever tricks like that?
6 Likes
Neat! But it only works if you hold the end of the fuse flat on the screen. If you hold it at an angle so you only have the edge of the fuse end cap touching the screen you don’t get sufficient capacitive coupling. Hence you can’t use a screwdriver as a smartscreen stylus - the tip is too small.
A compensation of wearing hearing aids is that if you put them on the Telecoil setting you can hold a hard disk up to your ear and very clearly hear it spin up (if it’s going to) and twitching the heads. (Sometimes when I come into London on Thameslink, if I’m sitting in a power carriage with my hearing aids on T I can hear all sorts of whirring and singing noises from the power electrics, and likewise if another train passes on an adjacent track.)
6 Likes
A lot of smartphone cameras pick up light some way into the infra red spectrum. So you can use them to see if a remote control is working, just by pointing it at the camera with a button held down, and watching in the camera app. This works best away from bright light, but you don’t need a dark room for it.
Obviously if you see nothing, though, it might be that your phone doesn’t do this. I know my phone can, I don’t know if it’s universal.
2 Likes
Haven’t tried recently but this trick used to work better with the front facing camera than the back one.
2 Likes
To determine the location of breaks in cables to a few millimetres in either power cables, or headphones, or fairy lights etc.
If you have something like a voltage detector pen, Aneng VC1017 in my case. Get an old electrically noisy usb1 wall-wort psu. Get any usb cable where the appliance side is broken. Chop off the end and separate all the wire and screen for about 4 or more inches. There is no need to bare the ends yet. Plug it all together, and with your voltage detector pen find the wire that generates the most noise the screen wire in my case). Bare the end of the wire that makes the most noise and connect a crocodile clip to it.
With the other end of the croc clip, connect it to your unpowered cable, and move your voltage pen along the surface. If there is a sudden drop of pen signal, the that is where the wire break is.
For power cables and mains lights, you no not need the usb setup, but it only measures the live wire. To measure the neutral wire, put a screwdriver in the earth pin to open the gate and put the plug in upside down.
Some multimeters do also have an EF mode, and it does sort of work, but they tend to lack sensitivity, and you have to clip the cable on both ends. The volt detector cost between £2-£4 on Ali. Dint get the one that talks, and personally I would not buy the one that measures voltage too, because you have to put your finger on a metal tab when measuring.
Dave, next time we are at an event, ask for a demo if you are interested.
2 Likes
I’ve been meaning to build one of these for years (from a 2008 Maxim Engineering Journal):
AC-Based Continuity Tester Finds Single-Ended Faults.pdf (952.7 KB)
(You could substitute the push-pull output MAX9022 with a cheap LM393 open collector output device by wiring the piezo buzzer to the positive rail instead of ground, and swapping the IN+ and IN- inputs to the outut stage.)
Well, to be honest, the device is based on the only signal injector and an amplifier principle.
The even easier way (if you have an oscilloscope) is to put one end of croc clip on the calibrate pin. the other to the cable under test. then wind an air coil of a few turns for the probe croc and probe clip.
The Aneng VC1017 is £2.50 on sale day, and after a few years the batteries seem to have become tight - either a poundland issue or the case is shrinking. Plus the ON button is in a really prominent position, so I use a sliver of plastic to separate the two poles of the batteries
Of course, that design is only a signal injector and amplifier. What did you expect? Magic?
And there are lots of things you can do with an oscilloscope, once you’ve got it out, found a spare mains socket or mains adapter, test leads or bits of wire, and fiddled with the attenuator, timebase, triggering mode and triggering level to get a nice green line.
But sometimes a self-contained gadget you can pull out of your bag, complete with test leads, which has actually been designed and in some sense tested and calibrated (unlike your bit of wire attached to your scope) is actually more convenient.