LM2907 Frequency to voltage Tac chip
metron9
Posts: 1,100
I have a question about the resistors on pins 3 and 5
Using the attached schematic, I am using a tachometer that has 0 to 8000 rpm output using 3mA per 1000 rpm.
Setting the pot on pin 5 and the frequency to 50hz I can adjust the meter to read 1000 rpm. All is well up to 4000 rpm but it will not go higher.
Puttering around as I usually do in the dark I reduced the 133k resistor to ground to 79K, re adjusted the meter to read 1000 at 50hz by adjusting the pot on pin 5 to 294 ohms. The meter is reading good all the way to 8000 rpm at 400hz (6 cylinder engine)
I would like to also make a switch that will allow 4 and 8 cylinder engines to use this as well.
Could someone explain the math I need to understand to adjust the resistor value on pin 3 and , is this the correct way to do this.
Second question:
I also have meters that only require .06ma per 1000 rpm. How can I reduce the 3ma to .06ma output for these meters?
Using the attached schematic, I am using a tachometer that has 0 to 8000 rpm output using 3mA per 1000 rpm.
Setting the pot on pin 5 and the frequency to 50hz I can adjust the meter to read 1000 rpm. All is well up to 4000 rpm but it will not go higher.
Puttering around as I usually do in the dark I reduced the 133k resistor to ground to 79K, re adjusted the meter to read 1000 at 50hz by adjusting the pot on pin 5 to 294 ohms. The meter is reading good all the way to 8000 rpm at 400hz (6 cylinder engine)
I would like to also make a switch that will allow 4 and 8 cylinder engines to use this as well.
Could someone explain the math I need to understand to adjust the resistor value on pin 3 and , is this the correct way to do this.
Second question:
I also have meters that only require .06ma per 1000 rpm. How can I reduce the 3ma to .06ma output for these meters?
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