Tools, Techniques and DIY Gizmos.

[HarryM1BYT]

Originally Posted by ceedy

A slightly more involved Electrikery thingy I knocked up years ago ..

Only a Dodgy rough Sketch ..



And a parts list from Maplins..and around the home .

Auto reset Fuse ............ AK12N
Resistor 300R...........2 off
Red Button push switch ......JB00A
Black Button Push switch ...JB01B
Bicolour LED .....................QY83E
LED holder to suit .............YY40T
Long case .........................FT31J
large RED croc clip............HF23A
Large Black Croc Clip.........HF23B
small black croc clip .........FK35Q
twin core household type lighting type wire about 5 metres ( to suit length of car) as long as its tough and flexible enough.
odd bits of Wire
Steel rod/long Nail for probe , stick some tape /heat shrink over most of it to stop any shorting out when probing .
The resistors are just to keep the LED from Blowing, so around the 300 ohms range will do .

If you can understand it all , piece of cake to knock up.

Just clip it on the battery and then using the long lead go around the car give any suspect electrical points a good probing ..

Basic circuit is here you can make it however you feel.

The resetable fuse is in case you short it out it will pop and reset after a few seconds

You could just use a fuse holder and blade fuse.

The probe is a bit of steel/brass rod with a point on the end.

NB .If you don't get the RED light testing on a known 12volt point the LED is wired the wrong way round.

Using the probe is quite straight forward by clipping the larger croc clips on the battery

And just using the probe on any connection yuo want to check, the 2 colour LED will show RED if the probed point is live
or show green if it is at earth.

You can also ( with care) Press either the RED button to inject 12 v into the probed point or press the black button to earth the probed point.

The small croc clip is just in case you need another earth point if you are probing some part that is isolated, eg ..mounted in plastic.

It doesn't measure Voltage or amps, use your multimeter for that .

Hope this may help someone... I've found it invaluable..

Chris

That is a design I seem to remember posting on here many years ago, but without any switches. I based mine on a design which I first came across whilst working for the GPO (BT) - which used two tiny 50v lamps in series, across the 50v DC supply and simply plugged into the racks. When plugged in, both lamps lit with a dim glow, proving the lamps. The probe was connected to the lamp series connection, so one would show a full light if the probe touched +ve and the other if it touched the -ve.

I built mine into a large hypodermic syringe, with the cannula replaced by a long sharp needle, so it could pierce cable insulation.

A simple idea, but very useful and which seems to have fallen out of use.