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Tachometer circuit needed
- Thread starter jddavis
- Start date
Do you have any kind of sensor to sense the speed of the axis and you want to amplify its signal?
or Do you want to build a tachometer entirely from the beginning and you want some ideas?
An LM2907/LM2917 seems like a good starting point.
You'd need at least a couple of decades of LM3914's just to get a rough idea of the engine's RPM range. If the RPM range of the engine was 0 to 7000, two decades would give you a resolution of 350 RPM, which is pretty doggone rough. Three decades would give you a resolution of 233.3 RPM per segment.
What's your RPM range, redline, and what resolution do you need?
You'd need at least a couple of decades of LM3914's just to get a rough idea of the engine's RPM range. If the RPM range of the engine was 0 to 7000, two decades would give you a resolution of 350 RPM, which is pretty doggone rough. Three decades would give you a resolution of 233.3 RPM per segment.
What's your RPM range, redline, and what resolution do you need?
I'm looking at National Semi May 2003 LM29x7 pdf page 10 top :
Voltage Driven Meter Engine RPM .
Has anyone built similar ?
Apparently one wire from "ignition" to pin 1 of LM29x7 .
Zener in LM2917 improves 0.3% accuracy ?
First breadboard for 4 cylinder 2002 Ford Escort ; max RPM 5000 ?
Why 400 Hz ~ 6000 ERPM - 8 cyl ?
Will decide LM3914 or LM3915 , 1 or 2 decades later .
Thanks , Jim D
Voltage Driven Meter Engine RPM .
Has anyone built similar ?
Apparently one wire from "ignition" to pin 1 of LM29x7 .
Zener in LM2917 improves 0.3% accuracy ?
First breadboard for 4 cylinder 2002 Ford Escort ; max RPM 5000 ?
Why 400 Hz ~ 6000 ERPM - 8 cyl ?
Will decide LM3914 or LM3915 , 1 or 2 decades later .
Thanks , Jim D
Hi Jim,
An LM3914 will produce a linear display, which is what you want.
An LM3915 will produce a logarithmic display, which would be of limited usefulness for your application.
The "ignition" lead would be from your ignition system's tachometer lead.
Don't know offhand why a Zener diode would improve accuracy.
For your engine specifications, consult your owner's manual, a repair manual, or your local Ford dealer.
Estimated RPM: In 4-cycle Otto engines, the crankshaft makes two revolutions per ignition. So, 6000/2=3000. Now we convert from RPM to RPS. 3000/60=50. In the example, 8 cylinders are given - so we multiply by 8. 50 x 8 = 400 Hz.
In the LM3814 datasheet that National Semiconductor provides, there are a number of examples of connecting the IC for display of multiple decades of LEDs.
An LM3914 will produce a linear display, which is what you want.
An LM3915 will produce a logarithmic display, which would be of limited usefulness for your application.
The "ignition" lead would be from your ignition system's tachometer lead.
Don't know offhand why a Zener diode would improve accuracy.
For your engine specifications, consult your owner's manual, a repair manual, or your local Ford dealer.
Estimated RPM: In 4-cycle Otto engines, the crankshaft makes two revolutions per ignition. So, 6000/2=3000. Now we convert from RPM to RPS. 3000/60=50. In the example, 8 cylinders are given - so we multiply by 8. 50 x 8 = 400 Hz.
In the LM3814 datasheet that National Semiconductor provides, there are a number of examples of connecting the IC for display of multiple decades of LEDs.
