Circuits by Tomi

PoE Powered Christmas Lights

Found some broken LED christmas lights (operated originally from 24V transformer) and a suitable spare switch mode power supply (36-72V to 24V). Then I got an idea to combine them to an experimental PoE Christmas light project. Circuit diagram: The circuit operation: Initially circuit presents around 23 kohms impedance when low voltage is on line

My DIY lab power supply

An adjustable regulated power supply is a necessary tool for an electronics laboratory. Here is a laboratory power supply 2.7-30V up to 4A I built has worked for 30 years ago and still going strong. Its function is to supply a stable voltage set by the voltage control potentiometer up to the current set by

VGA to SCART adapters

Some time ago I saw  The ultimate VGA to SCART adapter project at Hackaday with description: Accurate recreation of vintage arcades is becoming increasingly difficult. CRT monitors are rare nowadays and, even if you find one, it will probably not support the 15.7Khz horizontal frequency used by many old arcades. A good alternative is a

Enttec Open DMX DIY

DMX512 (Digital Multiplex) is a standard for digital communication networks that are commonly used to control stage lighting and effects. It was originally intended as a standardized method for controlling light dimmers up to 512 dimming channels. The first standard version was created in 1986, with subsequent revisions in 1990 leading to USITT DMX512/1990, ANSI

More measurement on Potato TDR circuit

This is a continuation to my recent potato chip to TDR circuit posting at Here are some measurement results made with high speed oscilloscope (at shortest pulse setting and 50 ohms impedance). Blue measurement with circuit directly connected to scope and yellow wirh 10x scope probe.

Potato chip to TDR circuit

A time-domain reflectometer (TDR) is an electronic instrument that uses time-domain reflectometry to characterize and locate faults in metallic cables. I designed a TDR circuit many years ago for easy cable testing with oscilloscope: That circuit was also turned to an electronics kit that is sold by Far Circuits. When getting the original 74AC14 seemed

Probing Ethernet cable with an oscilloscope

This article talks about measuring 10 Mbit/s (10Base-T) and 100 Mbit/s (100Base-TX) twisted pair Ethernet signals. Those standards use two wire pairs for the communications and use differential signaling. Differential signaling is a method for electrically transmitting information using two complementary signals. The technique sends the same electrical signal as a differential pair of signals,