Tach Output Problems

[Maxzillian]

I'm with a Formula SAE team running a KTM single and we're currently having some issues with our tach output wire on our Microsquirt. Yesterday it was working fine, but I was having trouble with the rpm reading in Megatune reading double (despite setting the engine as a 2 cylinder in constants since it was running wasted spark) so I updated the firmware to the current 2.88.j.c and updated Megatune as well. At that point we had solved our rpm issue, but the tach output ceased to work.

Our ignition setup is a VR trigger on a 36-1 crank driven wheel with the ignition drivers removed and the board jumpered to run a LS1 coil.

Is there a configuration for tach output that I'm missing or any cases of tach output not working with the current code?

[grippo]

Can you post your msq. Also I assume you only expect one ignition output, but is there any activity on the other output ? Is the first output completely dead ? Finally, what code version were you previously running ? I don't know if we have anyone using 2 cyl wasted, so we may have to play around with the configuration and/or code to get this to work.

[Maxzillian]

MT Version: 4.0
MS Signature: MSII Rev 2.88000

The previous firmware was 2.87, but I don't know which specific release it was.

We are expecting only one output since we are running a single coil and I can not check the second output easily since we burned up the driver and it has been removed. However, if it's really necessary, I can open the case and check it.

[grippo]

If this was working with 2.87 and doesn't work with 2.88, then either the new configuration(msq) is the problem or there is a code change issue that, while fixing the rpm issue, broke the tach output. To solve this I need you to post the msq file itself so that I can run your setup on the bench. Secondly, I need to know the exact code version that is in your microsquirt. It should be 2.883j, if not please download it and we will work with this version.

[Maxzillian]

My apologies. I should have known you wanted the file. We are running the 2.88.j.c code in the ecu right now. I uploaded it once tested, and then a second time to make sure it was a good load. It was also verified. The MSQ file is attached.

[grippo]

I tested your msq as is on the bench with a 36-1 wheel input running from 100 to 2000 rpm, up and down. The rpm was correct and the output also looked fine, providing a spark every 360 deg. So I'm not sure what the problem is with the output. I need to know if the output is dead or if there is sporadic activity.

After the first test I ran your msq in dual spark mode by selecting Dual Spark: single crank wheel under the advanced ignition option. I also changed the trigger offset to -336 deg to go with this option. The spark now fired every 720 deg on output 1 and same on output 2, but offset. So the sum of the 2 outputs gave the same frequency and phase timing as the original msq. However, this is a much more accurate mode, as it is based on tooth angle rather than time for the spark timing. To make it work for you, with a single coil input, you can set the No Skip Teeth to 18 instead of 36 and ignore the 2nd output. Or just use the 2nd ouput if it turns out the first output is broken. You could also use with 36 skip teeth, but you would have to combine the 2 ignition outputs into a logic chip with a single output. .

[Maxzillian]

Hmm, ok, I'll have to check the outputs. It just seemed odd that it'd stop working after a bootload. Granted, Murphey works in mysterious ways. ;)

Concerning the dual spark mode, why is this more accurate than running a single spark mode? By the sounds of it, the single spark mode uses a different timing logic than the dual spark setup since you mention one way is time based and the other is angle based. Or is this a required trick when using the -336 trigger offset?

[grippo]

Hmm, ok, I'll have to check the outputs. It just seemed odd that it'd stop working after a bootload. Granted, Murphey works in mysterious ways. ;)

Concerning the dual spark mode, why is this more accurate than running a single spark mode? By the sounds of it, the single spark mode uses a different timing logic than the dual spark setup since you mention one way is time based and the other is angle based. Or is this a required trick when using the -336 trigger offset?

I would try going back to 2.87 and see if the output is again correct.

As far as the non-dual vs dual spark mode, the former predicts when the next spark is going to arrive, then as each tooth comes in, it corrects for any error between predicted and actual tooth time. The angle-based algorithm calculates the spark angle in terms of teeth (like 10.76 teeth), then when it gets to 8 or 9 teeth later, it time predicts only for the 2.76 or 1.76 teeth to go. In theory both algorithms should work, but on the scope the tooth angle based is much better. I haven't done a mathematical error analysis to see why this is so.

The negative trigger offset must be used with the angle based because it sets up to fire the spark 2 tach periods ahead of the tach point at which it gets synch. (By tach point I mean whatever you choose as a cylinder event). At the next tach period, it again sets up for spark 2 periods down, but on the second output . In this alternating fashion there is a spark output for each cylinder. The reason for the 2 periods is that this gives sufficient time for charging the coil. Charge time is not so critical for 2 or 4 cylinders, but it is critical on 6 or 8 cylinders.

[Maxzillian]

I loaded the 2.87 code and the dash started working again. I also loaded the 2.881 code and it was working. I managed to dig up an oscilloscope and found that the 2.87 code and 2.881 code set the tachout to high (12V) when the engine is not running and goes low for 3-5 ms (approximately what our dwell time is) for each ignition event.

The 2.883 code sets the output to low when the engine is not running and goes high for approximately 0.15 ms for each ignition event. I'm willing to say that our tachometer can not read a pulse this short. It would likely work as long as the pulse is over 1-2 ms, whether it's going high or going low.

Thanks for the help!

[RedRocketRally]

Was this resolved? I'm using the 2.89 software on a ver2 microsquirt, with an Autometer tach.

I just hooked up my tachometer yesterday, but it doesn't move. It just sits on zero. I don't have an oscilloscope to check the output, but there is continuity from the ampseal pin 35 to the gauge. Any ideas?