EEVblog #267 - Voltage Detection Stick Teardown

It's Teardown Tuesday time.
Ever wondered what's inside those mains voltage detection sticks?
Dave cracks open an IDEAL VoltAware, and giggles at a patent.

[RRak]

Your determination to find out all the details about this design is remarkable. Thanks for sharing.

[rmasso]

Your best teardown video yet. Much better to go into the schematic, show wave forms and discuss the operation. Loved it. thanks.

[PatrykDarasz]

OMG you turned it on first! YOU TRAITOR! xD

[gnagyusa]

Cool post! Who knew that you can learn so much from the humble non-contact probe.

[EEVblog]

I can confirm the 22M (with a cap in parallel) is in series with the input.

[gmanutube]

Good work, Dave. When you brought up the patent, it matched pretty well. I've had dealings with SCC in the past. They also made after-market inkjet cartridges and blanked the ICs in those. Of course the blanked parts were just std parts.

[vladnickul]

On polishied out chips sometimes you can see the numbers if you wet then...

[JosefdeJoanelli]

I think that SOP package is Texas instruments branded. U can just see the one side of the TI logo I reckon.

[AuctorisVideo]

Another great video Dave. Love the board microscopy, worked really well.

[nThanksForAllTheFish]

Excellent video Dave. I think it may be useful to consider that the whole circuit is floating with a small capacitance (2p?) to the source and a larger capacitance (100p?) to the user/Gnd. It would then be important to ensure sufficient lag between the input and gnd terminal of the schmitt input, which might explain the cap in parallel with the 22M as well as the fact that the battery negative terminal (body) is towards the front of the probe where the user's finger is likely to be.

[DasIllu]

I use sticks like that ONLY to trace wires in walls or get a quick overview. Never ever use them to check that a wire is cold. It can get you killed. Also never use a crappy multimeters for tasks like that for they often give you false positive results (as the sticks do, too).
For stuff like that i use my Benning Duspol analog tester.

[TilmanBaumann]

Love the microscope technique. That helps a lot

[BrettW]

Only you Dave could create an 18 minute video on something so relatively simple.

[joelwisman]

Long ago jumped to automotive, but when I was a supervising industrial electrician, I forbade contact voltage detectors because they become a bomb if unknowingly used on medium voltage high power circuits. If where you work does not have any high power medium or high voltage, the danger is reduced, but have still seen good quality giggers and lights blow for no apparent reason.

Just as with contact voltage detectors, you need to test on known live circuit to confirm operation.

[EEVblog]

I need to get a real microscope camera though. It's not easy holding the camera a certain distance away from the eyepiece, at a certain angle, and talking whilst adjusting the microscope and/or object!

[ChaplainDaveSparks]

Nerd? I'll give you nerd! When I was working on my BSEE degree in 1972, we had to learn to use a SLIDE RULE! I wore it proudly in its scabbard on my belt. Later on it was my trusty TI SR-10 electronic calculator (because I could afford an HP 35 with its cult-like RPN operation). :-)

[shaunclarke]

The older models did, but the newer ones don't seem to.

I don't know if there was a technical reason for the change such as battery life, or if it was done to add sort of a POST by having the unit beep and light up when first turned on - presumably so you'd know the difference between a flat battery and a dead cable (although you can of course just check it with a known live cable also).

[Milosz_Ostrow]

The resistor in series with the antenna isn't necessary, unless you're modeling the plastic insulator covering the antenna.

[johnclawed]

It has 2x 14 pin chips and 3x as many discreets as the patent. All for an LED and a buzzer?

[CampKohler]

For a patent, the values are not what is important, but theory of how the parts work to perform the function. In other words, if you had patented the original mouse with a certain size ball, you couldn't get around the patent by having bigger balls. No, wait... that didn't come out right..