Adapting Lightspeed tach output for Vans Tach

[rainsal]

Hello :-)

I have a Lightspeed iginition and a Vans Tachometer. I am not able to use either of the Vans tach drive sender units.

The Lightspeed box outputs 4 10v 3.0ms pulses per RPM and the Vans Tachometer requires 8 pulses per RPM ( requires a 5v to 15v pulse signal).

Consequently my guage runs at exacty half real RPM.

Has anybody created some sort of device that doubles the 4 pulses/RPM to 8 pulses/RPM ....so that the tach reads correctly .....


or.......

does anybody know of any way to modify the internal of the Vans Tach itself to read twice as much as it does currently ?

Any suggestions greatly appreciated :-)


many thanks

Rainer

[Walter Klatt]

Don't think I can help you with your specific problem. But I also am having trouble getting my electronic tach (not a Vans) to work with the LSE tach pulse output.

How did you even measure if the LSE is working? Right now my tach is reading 0. It seems like there is no signal at all from the LSE. I have a regular volt/ohm meter. Should it show a pulse signal over 10V if the LSE is working?

Walter

[elippse]

Until recently the LSE tach output was a +10V, 1.4 mS pulse on the PIII or a 300uS pulse with a PII. Recent units have an opto-coupler output which may be configured as a +pulse or - pulse, open collector or open emitter. In the open C configuration it relies on a voltage source at the load with a series resistor, such as 1k to 10k, or with the open emitter it relies on a resistor to ground at the load end. Opening up the circuit may not show any voltage.

[gmcjetpilot]

My bottom line:

#1 suggestion first, can the Van Tach and get a different tach that will work with the Lightspeed.

#2 get a digital volt meter and use it as a Tach (Lightspeed has output to read tach and MAP direct)

Most digital tachs (EFIS) have a setting selector for number of pulse per RPM, 1 or 2 or 4 or what ever.

Most of the Hall Effect tach senders send two pulse per turn of sender, however since the tach drive turns 1/2 crank rpm as does the cam, it ends up equaling 1 pulse per crank rotation.

Vans tach sender you say is 8 pulse per rotation of the CRANK! Or is that 8 pulse per sender rotation, which would be 4 pulse per crank rotation.

Being an electronic hobbyist there is a way to turn 1 pulse into 4 or 8 pulse. A little black box to convert. I don't think that's worth the effort. Are you sure you must have a Van tach?

The other way, take the tach apart and change or modify it somehow?

If you want a cheap small electric tachometer with analog display consider some car stuff. They make 2-1/16" gauges. They have selectable pulse settings. The down side is most will go to at least 5,000 rpm. YOU COULD get say a 6,000 RPM tach and set the pulse to read half and RE FACE the tach to match the Van gauges?

[Walter Klatt]

As I said, mine is not a Van tach. It is called a SmartTach by DPS Instruments, long out of business. It has served me well, though, for many years, and would like to continue using it.

Previously, it ran off my old Bendix mag with a 3 wire pick-up that screwed into the vent hole. This was a hall-effect sensor.

I recently installed a new engine with the LSE Plasma III, and wanted to use the pulse signal from the input connector. I have now tested and determined that I am indeed getting 2 pulses per rev, so I know the LSE signal wire is working. But my tach is not picking it up for some reason.

The DPS tach is fully programmable to configure the right number of pulses, etc. The problem is that it won't recognize the LSE signal at all. The DPS tach is supposed to recognize a pulse that is over 5V and less than 7/10 volts in a cycle.

Walter

[gmcjetpilot]

Originally Posted by Walter Klatt

Previously, it ran off my old Bendix mag with a 3 wire pick-up that screwed into the vent hole. This was a hall-effect sensor.

I recently installed a new engine with the LSE Plasma III, and wanted to use the pulse signal from the input connector. I have now tested and determined that I am indeed getting 2 pulses per rev, so I know the LSE signal wire is working. But my tach is not picking it up for some reason.

The DPS tach is fully programmable to configure the right number of pulses, etc. The problem is that it won't recognize the LSE signal at all. The DPS tach is supposed to recognize a pulse that is over 5V and less than 7/10 volts in a cycle.

Walter

Sorry Walter I was replying to the original thread starter Rainer. "elippse's" answer was more on target. So the question is "for some reason". First you have to write or call Klaus and see what design tach output your model/serial number has. I don't know if you followed elippses post, but he's talking about a transistors collector & emitter. The third terminal on a typical transistor is the base. Apparently Klaus included some more flexibility in his tach sending electrical architecture. I do know early early LS ignitions did have short duration pulses, which caused issues with some tachs. I recall he opened the duration up from early units. Really Klaus is going to be your source. I was not aware of this change but it makes sense. As elippse said you might need a resistor load.

It sounds from what elippse said the later LS models might just take a resistor or alternative wiring to make it swing. If that does not help, write me direct. I might be able to make up a circuit to filter / boost the signal for your tach (if needed). From what ellipse said the new design LS units have different tach configuration options, which should be able to drive you gauge. Right now I'm gussing because I'm familiar with older LS units.

Have you tested your tach with a pulse or signal generator to see what it (really) takes to make it swing. It is possible you have some component in the tach like a capacitor decaying from age that needs replacing.

Good luck.

[deene]

The way to double the pulse frequency is to use a PLL (Phase-locked-loop) circuit. Chip versions exist and are not expensive. Long, long ago (right out of grad school) my first design assignment at TI was to design a PLL to allow disk logic to follow the changing speed of the disk (to increase the usable capacity from the newly available 12 inch, 1 megabyte disk drive, which just goes to date my engineering career).

PLL's are now widely used on microprocessor chips to generate the high gigahertz clocks needed by the processor from lower input clock frequencies.

The 1:2 PLL uses a divide by 2 in the feedback loop and thus the output runs at exactly twice the input frequency.

I would try to do a quick design, but being retired, my EE skills have left me...except for what is needed to hook up my AFS 3500 in my RV8 (grin, grin, ...).

[Walter Klatt]

Originally Posted by gmcjetpilot

Sorry Walter. "elippse's" answer was more on target. So the question is "for some reason". First you have to write or call Klaus and see what design tach output your model/serial number has. I don't know if you followed elippses post, but he's talking about a transistors collector & emitter. The third terminal on a typical transistor is the base. Apparently Klaus included some more flexibility in his tach sending electrical architecture. I do know early early LS ignitions did have short duration pulses, which caused issues with some tachs. I recall he opened the duration up from early units. Really Klaus is going to be your source. I was not aware of this change but it makes sense. As elippse said you might need a resistor load.

It sounds from what elippse said the later LS models might just take a resistor or alternative wiring to make it swing. If that does not help, write me direct. I might be able to make up a circuit to filter / boost the signal for your tach (if needed). From what ellipse said the new design LS units have different tach configuration options, which should be able to drive you gauge. Right now I'm gussing because I'm familiar with older LS units.

Have you tested your tach with a pulse or signal generator to see what it (really) takes to make it swing. It is possible you have some component in the tach like a capacitor decaying from age that needs replacing.

Good luck.

George, I have corresponded with Klaus on email, but he has not been able to help me so far. In fariness to him, it seems that the Plasma III is working, so it is not a problem with his product.

My challenge is to figure out to correctly wire my DPS SmartTach to work with the pulse signal from the EI. Klaus was familiar with my tach, and said it should work, but didn't tell me how to hook it up.

As I have mentioned, I have used this tach for many years off a mag hall sensor pick-up (3 wires), so I know it works, too.

George, if you are willing to take a crack at it, I can send you a private email with the intructions from my DPS manual, and feel free to see if you can figure it out. Any help is welcome.

Walter

[gmcjetpilot]

Originally Posted by Walter Klatt

George, if you are willing to take a crack at it, I can send you a private email with the intructions from my DPS manual, and feel free to see if you can figure it out. Any help is welcome. Walter

Shoot it to me, email is in my profile.

[Walter Klatt]

Finally got my tach working, but not with my LSE Plasma III as I had hoped. Went back to using a hall effect pick-up for my one Slick mag. As it happens, a hangar neighbour had a spare sensor (from Westach), so I tried it, and success at last.

There is actually an advantage with the sensor running off the mag. If it was off the LSE, you would lose your RPM signal when switching the key to mag only, and you would not know the exact mag drop. With the hall effect sensor, the signal is always working, and you always get an accurate reading when testing LSE only or mag only.

Thanks to all those that offered help and advice. In the end, I learned a few things, too.

Weather is supposed to be good tomorrow, so am planning my first test flight with the new engine.

Walter