It is based in the VCRGB Software shown here.
The circuit measures the engine RPM (or Speed) and changes the color of an Instrument illumination (or whole
Dashboard), dependent of the RPM
The senitivity / RPM Levels can be adjusted
High RPM :Red
The use of modern ultrabright LED's allowth this circuit to be operaten in many applications.
R1 470 Ohm
C3 4.7 uF
C6 100nF Keramik
R11, 12,13 150-270 Ohm, je nach LED's
D2 7.5V Siehe Text
The Operating Voltage is connected to Pad1/2 and powers a LM2907/2917 Frequency/Voltage-Converter.
The RPM Signal (connected to Breaker or Tacho Signal Generator) is connected to PAD3.
The LM2907 converts the Frequency (proportional to engine RPM) to a corresponding Voltage, which is used by the Atmel Tiny15 to control the LED's.
With R6 you can adjust Sensitivity, with R7 you can adjust for idle RPM.
The Microcontroller has a 5V Regulator for proper operation.
The LM2917 has a builtin Z-Diode. When using a LM2907, you must use a Z-Diode D2 of about 7.5V to stabilize the Supply Voltage of IC1.
The Controller has to be programmed with this Software
Additional Information,Basics,DIY Kit, Links for Schematic