I'm trying to develop an LED tach display that will progressively light LED's as the RPM's increase and was wondering what type of signal is carried on the tach signal line. Or if anyone has schematics of a circuit built for this type of application that would be great as well. Thanks for all the help!
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Tach signal information 1
- Thread starter relic7
- Start date
Tach signals vary depending upon where the signal originates from. On an ECU engine, or engine with a more modern ignition module, the signal is frequently a TTL or open collector pulse - one pulse for each spark-plug firing.
Many marine engines, and early ECU or Pre-ECU engines, or engines where the ignition module is an earlier solid-state or point ignition, the 'tach' signal is from the switched side of the coil, and an input protection circuit/basic filter may be needed for your circuit (the ignition coil will spike and ring some). Again, the tach signal is one pulse for each spark-plug firing.
On Diesel engines, a tach pickup is used - usually a gear-tooth sensor on the flywheel or a "tach generator" driven from the injection pump shaft. A tach for these will need to divide-down the number of counts to get to RPM. Tach-gens and geartooth sensors are a sinusoidal output-which are usually less than a volt peak-peak at idle to several tens of volts peak-peak at high RPM. Some newer diesels may have a ECU tach output similar to a regular gasoline ECU engine.
Alternately, on some outboard motors, and some diesel engines, the tach signal is derived from the pre-rectified AC signal of the alternator. In these applications, the poles of the alternator and the belt ratio needs to be taken into account to get RPM. The AC signal may be several tens of volts peak-peak, and may have some spike noise. Belt wear and slippage makes this means less accurate than others.
Many marine engines, and early ECU or Pre-ECU engines, or engines where the ignition module is an earlier solid-state or point ignition, the 'tach' signal is from the switched side of the coil, and an input protection circuit/basic filter may be needed for your circuit (the ignition coil will spike and ring some). Again, the tach signal is one pulse for each spark-plug firing.
On Diesel engines, a tach pickup is used - usually a gear-tooth sensor on the flywheel or a "tach generator" driven from the injection pump shaft. A tach for these will need to divide-down the number of counts to get to RPM. Tach-gens and geartooth sensors are a sinusoidal output-which are usually less than a volt peak-peak at idle to several tens of volts peak-peak at high RPM. Some newer diesels may have a ECU tach output similar to a regular gasoline ECU engine.
Alternately, on some outboard motors, and some diesel engines, the tach signal is derived from the pre-rectified AC signal of the alternator. In these applications, the poles of the alternator and the belt ratio needs to be taken into account to get RPM. The AC signal may be several tens of volts peak-peak, and may have some spike noise. Belt wear and slippage makes this means less accurate than others.
secretplayer
Mechanical
-
1
- #4
I think relic7 wanted to build one himself, not spend $99 on one...
Try this:
let us know how you get on!
Stu
Try this:
let us know how you get on!
Stu
The circuit in the link above is like one I made 10 years ago for a motorcycle engine tach. A LM2907 frequency to voltage converter in conjunction with 3 LM3914 bar graph displays. I used multiple bar graph drivers with their internal 1.25V references wired in series to get 30 LEDs, and thats all I needed for an LED tach. This is probably the easiest way to do it.
Brad
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