Circuits by Tomi

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,

Avalanche pulse generator circuit

Pulse generator is an electronic test equipment used to generate rectangular pulses. Pulses are typically injected into a device that is under test and used as a stimulus or clock signal or analyzed as they progress through the device, confirming the proper operation of the device or pinpointing a fault in the device. Typical application

IoT Temperature Meter

This is a test project to build IoT temperature meter using ESP8266 WiFi module, DS18b20 temperature sensor and nodemcu. It sends temperature data to ThingSpeak. This test is based on ESP8266 + ds18b20 + thingspeak+ nodemcu article and it’s files on GitHub plus ds18b20.lua. ESP8266 + ds18b20 + thingspeak+ nodemcu article describes how to build

AD9850 scalar network analyzer

A network analyzer is an instrument that measures the network parameters of electrical networks. Today, network analyzers commonly measure s–parameters. Full featured network analyzers are expensive instruments, and sometimes a simpler. Scalar Network Analyzer (SNA) is a simpler form of RF network analyzer that only measures the amplitude properties of the device under test.  SNA is

Diode detector for RF

Here is a simple diode detector for RF signals. I can feed RF signal from left and get DC output from right. The DC output can be fed to Arduino analog in. The diode in the circuit is germanium diode for low voltage drop. The circuit works well for fractions of volts to several volts

AD9850 based signal generator

Few days ago I tested AD9850 DDS module in home in hope to some day have a working signal generator using it. The initial tests went well, so I could plan the next step. I was already doing some information searching to make decision if I should do the controlling using web interface (with Ethernet