hi,
i was looking into making a shift light for a friends car (and mine while im at it probably ), and then i came across a thread on here (was only one post with no replies, and i can't seem to find it again now) where someone was using a LM3914, which lights 10 LEDS in a bar or dot graph depending on an input voltage and reference voltage. this was very exciting, so i thought i would look into making a similar style circuit.
the problem i have is, the lm3914 uses a voltage, though i want to have the LEDs light up in response to the tacho feed frequency increasing. i found that my car produces 250 beats per minute for every 100rpm. knowing this, could i use a capacitor to smooth the wave to a reasonably constant voltage, so that the voltage across the capacitor would increase as the frequency increases? the problem would then arise that the tacho may not function properly, as the input it recieves (normally a frequency) would also be affected by the capacitor, so it would now be recieving a voltage, which probably wouldn't have the same effect. to solve this i thought i could use a transistor to amplify the signal, so it should leave the original signal intact, and then smooth out the amplified signal...?
the other option, though less preffered due to cost and complexity, would be to use a LM2907 or LM2917 wich produces a varying voltage relative to a frequency input, which i could then feed to the LM3914.
any advice will be greatly appreciated, and please point out any faults in this idea
i was looking into making a shift light for a friends car (and mine while im at it probably ), and then i came across a thread on here (was only one post with no replies, and i can't seem to find it again now) where someone was using a LM3914, which lights 10 LEDS in a bar or dot graph depending on an input voltage and reference voltage. this was very exciting, so i thought i would look into making a similar style circuit.
the problem i have is, the lm3914 uses a voltage, though i want to have the LEDs light up in response to the tacho feed frequency increasing. i found that my car produces 250 beats per minute for every 100rpm. knowing this, could i use a capacitor to smooth the wave to a reasonably constant voltage, so that the voltage across the capacitor would increase as the frequency increases? the problem would then arise that the tacho may not function properly, as the input it recieves (normally a frequency) would also be affected by the capacitor, so it would now be recieving a voltage, which probably wouldn't have the same effect. to solve this i thought i could use a transistor to amplify the signal, so it should leave the original signal intact, and then smooth out the amplified signal...?
the other option, though less preffered due to cost and complexity, would be to use a LM2907 or LM2917 wich produces a varying voltage relative to a frequency input, which i could then feed to the LM3914.
any advice will be greatly appreciated, and please point out any faults in this idea