This mini DigiThermo is a device specially designed for measuring and time and temperature in chemistry laboratory.

The following picture demonstrates the circuit diagram of DigiThermo. Read more »

This temperature may look like several dozens thermostats that measure temperature and performs some action (switches relay) when temperature threshold is reached. Actually this is what this one does - it activates a relay with fan connected when temperature reaches 40ºC.

There is another thing what makes this device little bit different from others - it accepts TV remote control commands. By pressing 1, 2, 3 and 4 buttons each of four relays can be turned ON/OFF manually. Design is based on AT89C51 microcontroller which reads LM35 temperature sensor data via ADC0804 ADC. Compares temperature value to given threshold and in case of alarm it sends relay activation signal via ULN2003 Darlington transistor array chip. Grab project files, build and keep things cool.

Nokia 3310 graphical display seems to be very popular among embedded hobbyists. Probably because of it’s availability, lots of examples over the internet and simplicity of interfacing. Wichit Sirichote has developed simple scope application by using his project 8051SBC board.

Interfacing of display is very simple as it uses serial interface. The only thing you should take care when using 5V logic is to reduce LCD voltage to 3V level. This can be simply done by using two general purpose diodes connected in series. This provides approximately 1.4V drop. Source code is available for your experiments. Also you can see live action of this simple scope in this video. Of course this scope can’t assure you proper characteristics but this example gives you great info about interfacing 3310 LCD.

This is really low budget frequency counter as it uses only microcontroller and standard LCD indicator.

It can be used for calibrating of other devices like frequency generators or simply measuring unknown frequencies. Assembly routine can be downloaded here.

There may be some situations when it is hard to use a tachometer only because it is impossible to read revolutions per minute mechanically. The only way is to read RPM without touching rotating shaft.

This great design was constructed by Ibrahim Kamal who used an IR signal to transmit and receive it reflected from reflective stripe fixed to rotating shaft. Device is controlled by AT89S52 microcontroller which counts reflected pulses and displays value on LCD. RPM counting algorithm uses last three times between pulses and this way constantly gives instant RPM value. RPM meter consists of two parts: microcontroller board and IR proximity sensor connected to microcontroller board via simple 4 wire cable. Project files are available for download in a single zip.