The author made the project for a friend who wanted to include it into an amplifier as an extra function. The project turned out really well and it works flawless. It’s based on the ATmega8 and it uses a 4 digit 7 segments common anodes led display to show the time. The code is pretty simple, written in C, but it lacks comments as the author did not felt the need to add them.
4 Digit ATmega8 Clock: [Link]
This schematic is ment to digitally display the output of an electronic Swissflow SF800 flow sensor. This sensor puts out an open collector square wave signal (like a fan RPM monitoring signal) between 50Hz (=0.5 liter/minute) and 2000Hz (=20 liter/minute).
By dividing the measured frequency by 10 and putting the decimal point at the right place you get directly a display in liter/minute. I don’t use the first digit output (output D) from the 74C925 to obtain a display of 10 to 9990Hz or xx.x liter/minute.
3-Digit Frequency Meter: [Link]
Mobile infrared electronic transmitter