A microcontroller based automobile digital RPM meter

Some of the smaller cars available today does not have an RPM meter on them – this would be some trouble since you wont be able to determine the actual speed of the car’s engine, thus will have an impact on the fuel consumption since engines are efficient at a certain range of shaft speed. This project makes use of an AVR microcontroller and a signal conditioning circuit that makes use of an LM324 operational amplifier (Op-Amp). The input signal was taken from the High Voltage (HV line) of the main distributor of the engine. This specific point was chosen since all (gasoline) engines have an HV line. The signal from the HV line is fed into the signal conditioning circuit before being fed to the microcontroller’s PB1 pin. The Timer/Counter1 External Counter Input mode of the PB1 pin is used as an external clocking source for the MCU’s timer1 making it able to do frequency measurements. While another timer (timer0) is used to measure the elapsed time. If you wonder whats in the HV line that makes it a good… Continue reading

Stand alone CPU cooler fan speed tester

PC can display CPU fan speed via simple application. Another option is to go to BIOS menu and read fan speed value. But if you want to have stand alone device that measures CPU cooler fan speed so here it is. It is a PIC16F627 based fan tester with four 7 segment LED displays. CPU fan sends tachometric pulses via separate wire and can be calculated as RPM. PIC captures and calculates the time by using two timers/counters. One captures pulses and another calculates elapsed time. For instance, by capturing the amount of pulses within the period of 1 second would yield the frequency at which the fan spins, e.g. 60Hz. To convert to RPM it is a simple matter of multiplying the frequency in Hz by 60, which in this case yields to 3600 RPM. Schematic is simple – the most components are used for interfacing LED displays. They are controlled via BCD converter and transistor keys. Fan pulse wire connects directly to PIC pin via pull-up resistor as amplitude of fan pulses is same as PIC power supply… Continue reading

Contact-less tachometer counts up to 99kRPM

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. Continue reading