This digital speedometer project was built to replace unreliable analog speedometer of 1971 Datsun 1200. The circuit uses digital IC like 555 timer, 4017 CMOS decade counter, 74C14 hex schmitt trigger inverter, 4553 CMOS 3-digit BCD counter and IC6 4511 seven-segment decoder/driver. This car speedometer project is equipped with two strong magnets to the tailshaft placed behind the gearbox and coil from some electro-mechanical device as sensor and 4-digit 7-segment as display.
“The circuit was calibrated by feeding a low voltage 50Hz AC signal circuit into the sensor input, and then adjusting VR1 and VR2 until the Speedo reading was correct. To determine the correct Speedo reading with an input signal of 50Hz, you’ll need to measure the circumference of one of the rear wheels, and also determine the diff ratio”, said Martin Pot, the designer.
Project Firmware, Schematic and Documentation