With two cheap integrated circuits and a few parts from the ‘junkbox’, this very simple and useful circuit, can be put together in just a few hours.
This cable tester, tests all the 8 wires in a network cable in one move, if one of the 8 LEDs does not lit up, it means that the wire corresponding to that LED is faulty.
- 1 x 4017 decade counter,
- 1 x 555 timer,
- 8 x LEDs,
- 2 x 8P8C modular connector (RJ45),
- 8 x 100Ω resistor,
- 1 x 10KΩ resistor,
- 1 x 15KΩ resistor,
- 1 x 4,7µF capacitor.
The yellow LED has no special significance, I only had 7 green LEDs.
For some time I felt the need of an USB charger in my car, but all the commercial ones I’ve seen haven’t convinced me they are reliable. So I proposed myself to build one which would have to be “virtually indestructible”, stable and safe for the devices I connect to it.
I remembered that I had a LM340KC-5.0 (5V positive regulator in TO-3 case), laying around somewhere, and told myself that this is perfect for the job. After I looked over the datasheet, I did a test circuit, and it performed perfectly.
I bought a telephone outlet to use it as a case, and I mounted two USB receptacles (which I dismembered from an old computer motherboard) instead of the telephone jack, and the LM340 on top of the case.
The USB pins configuration you can find on Wikipedia.
I have also added a green LED to know if is working.