Hobby Projects - Insulation tester, LED Circuits, Meters.
Showing posts with label Schoodles. Show all posts
Showing posts with label Schoodles. Show all posts

Friday, March 11, 2016

Electrician Tool – Continuity Tester

I had gone to buy some long wires at a electrician shop, when a terminal box had to be tested, he used a continuity tester.

Continuity Tester
When i used to buy electrical parts in the past, they used a tester box, made of wood. This had a bulb and a tubelight starter and two long wires (230v AC). The Continuity tester would light up a 40w lamp. Now he had a LED based one, so i got one for myself.

All it had, was two small cells in a plastic box with a LED, i was just flashing the LED as it looked nice thru the transparent box, it failed. The LED had burnt, the battery used. This product was not for monkeying around.

Now i performed a tiny design upgrade, I used a extra-bright 3mm Red LED with a 47 ohm resistor. Now it is robust, at least for continuity. The battery life can be good only if you make quick checks.

Improvements -

More protection may be needed to avoid damage to LED when this tester is applied across a battery by mistake. LED can flash to save battery power, one SMD - LM339 can be used for flashing and a more efficient short-leakage detector. A small oscillator with a neon may be more efficient and bright. This can also double up as a hidden Live wire or Mains AC detector.

Continuity Tester Circuit

A single chip metal detector with a range of a few inches. This is useful for detecting nails or screws in walls and floors, or for locating buried mains cable.

Friday, August 13, 2010

Emergency Light with Fluorescent Tubes

Emergency Light for Portable Use. Note Charger and Battery not Shown. Design from Ludens
12 Volt fluorescent lamp drivers: Three schematics of 12 V drivers for 2, 8 and 20 Watt, plus a lot of explanations about fluorescent tubes. Use the drivers for camping, emergency, boating, etc.

Emergency Light with Fluorescent Tubes

Improper Design of Magnetics or Testing at low voltages can damage the switching NPN. The NPN must have fast switching time, see towers for Cob in pF and .fT in MHz. This may Oscillate for 100 kHz so it has to switch fast, then less heating and better beta at high freq. Choose such a NPN.
The Ic or max current of the NPN can be few times above the current consumption you have planned with the gadget. As a thumb rule if this is a 10W at 10V that means 1 Amp current. Hence choose a device 5 times above 1 A. Use a 5 A device or a 7 A for reliability.

The voltage selection of NPN must also take into account the transients in the switching. If its a sine oscillator like above, the transients, spikes are mild but in square wave switching, the spikes can be very sharp on resonance. These low energy zaps can weaken the NPN and deteriorate its switching and cause heating and eventual failure. So many CFL lamps and Emergency Light's fail quickly as they are not built robustly.

Even this circuit above is good only if is built very carefully.

Tuesday, July 13, 2010

Powered USB Hub Help PC Interface

I got a strange problem as i added more and more peripherals, the pc gave odd messages, "i cannot detect what you are doing" and things like that. I almost flipped trying to locate the culprit. The problem was not in any peripheral but in the USB port powering the system itself. The SMPS was not loading much. Certainly the peripherals were drawing more and the warning could have been more like "use your own power".  Computer Data Interface

Powered USB Hub Help PC Interface

I could not locate a powered USB with any vendor close by, so i built one and it works perfectly, Now it doubles up as a UPS Low Batter Indicator, by rare coincidence. If the Unregulated DC is above 7 volts, then no bugs. When i adjust the unregulated DC to the 7805 to around 6.9V, then i have a advance warning system.

Wireless USB - Wireless Extension to USB

USB Hub with Power

When power fails, i keep working and listening to music from a Flash Thumb drive. When music stops, i turn of computer, the lead acid batteries gone below 20 V DC. This avoids deep discharge of my batteries. The Powered USB gets undetected when the supply falls below 4.5 probably.

Monday, July 12, 2010

Charger for Portable Devices like iPod

This is a simple charger you can build for devices like iPod or iPhone. It works for ipod touch. It can be modified for any device. This may need no modification for devices that are charged using PC USB port.

Power Electronic Circuits

Charger for Portable Devices like iPod

This is a Schematic Doodle called Schoodle. Use it for Learning and understanding. Build and test only when you have practiced and gone beyond simple electrical and electronic circuits. Mistakes can damage your portable device or even waste your components. Hence take care, work systematically, not like me. See the mess i have created below.