Repairing a failed Fluke 1AC Voltage Detection Stick

This is an early NCV (Non Contact Voltage) detector that uses a ceramic PCB with printed resistors.
I wonder if they used a ceramic substrate to give high stability at the very low currents involved in sensing electric fields.

The quality of the construction was also the downfall of the early units, since they used a rugged metal body. That feature was pounced on by the department of highly improbable electrical accidents, as posing a risk to unskilled labour who might shove it in amongst random live metalwork.

The principle of these things is that a capacitively coupled field is amplified and then used to drive an LED. In this particular unit there is a six-gate schottky inverter used to filter AC (already done by the detection method) and then drive a charge pump to get a decisive LED indication of a valid detection.

I get the feeling that the person who designed this went by the book and built it out of standard logical sections, but in doing so may have overengineered the design slightly.

I also looked at a much simpler version which uses one resistor, three cheap transistors and an LED to achieve the same effect. The cheaper version is the most common these days, but it’s worth noting that some other clone units have clearly been “inspired” by the circuitry of the original design.

The classic neon test screwdriver has been around for a long time. It relies on the sensitivity of a small neon indicator bulb in series with a safety resistor to give a slight glow when touched to live electrical connections by finding a return current path through the user.

It has a few weaknesses. It’s very dim to start with, but even dimmer when the user is well insulated from ground, some have inadequate safety resistors, and it’s a very vague test that is not always reliable.

With the sensitivity of modern LEDs I thought it might be worth testing to see if they could be substituted in place of the original neon indicator to provide a brighter indication.

Note that this experiment involves direct electrical contact with mains referenced circuitry. It is imperative that the resistor is chosen with safety in mind, and that the internal wiring can’t short out the safety resistor accidentally.

WOW! AC VOLTAGE Detector Circuit?! Can It Be?!
https://www.youtube.com/watch?v=D2ekBjrHzYo

How Non-Contact Voltage Testers Work:
https://youtu.be/D2ekBjrHzYo

A very simple device. I’ve never really considered that LCDs have an accurate threshold voltage at which a segment will change state. I get the feeling this display has a higher voltage than average.

The use of printed resistors is an interesting evolution from the traditional surface mount ones. I suppose that a variation in carbon ink thickness isn’t too critical as it still results in an equally scaled voltage divider.

This NodeMCU Circuit Finder Takes the Yelling out of Finding the Right Circuit Breaker
https://www.hackster.io/news/this-nodemcu-circuit-finder-takes-the-yelling-out-of-finding-the-right-circuit-breaker-48333a506591

Designed for silent notification when you’ve flipped the right switch, this server-client setup works via Wi-Fi.

Pseudonymous maker “ThinkLearnDo” and his father have turned to a pair of NodeMCU microcontroller development boards to assist with a home improvement task: figuring out which circuit breaker goes with a given socket.

“My dad was having to deal with finding out which plug receptacle is connected to which circuit at work,” ThinkLearnDo explains. “He came up with a simple idea of using NodeMCUs to help solve that problem. This is the result.”

The idea is relatively simple: One of the two NodeMCU boards, which include Wi-Fi connectivity on-board, is configured as an access point and listens out for UDP packets sent to its address; the other NodeMCU connects to said access point and begins transmitting the packets.

So long as the stream of packets is uninterrupted, the NodeMCU’s on-board LED will remain lit. Should one of the two NodeMCUs switch off — because, say, you’ve toggled the circuit breaker controlling the power socket to which it’s connected — the LED goes out.

It’s a neat solution to the problem, though one which has long been solved by commercial socket testers with audible “everything’s fine” alarms — or the low-tech alternative of someone shouting to tell you when a lamp goes off.

ThinkLearnDo’s version, though, has a couple of advantages: It’s silent and won’t disturb others in a shared environment, though flipping circuit breakers randomly until you find the one you need might

https://github.com/thinklearndo/circuitbreaker