Author Topic: coil trigger signal and electronic tach (Read 20597 times)

tsflstb · « **on:** March 28, 2008, 09:33:50 PM »

Installed a Dyna S ignition on my 400F. It's working like it should. One thing I hoped it would remedy was a poor signal to my electronic tach. The tach is more responsive now, but seems to be reading 1/2 the actual RPM. It's an automotive tach from Summit. It has a 4, 6, and 8 cylinder mode. The 4 cyl mode gives me the highest reading and what looks like 1/2 the actual. I need to hook the mechanical unit back up to compare them at some point.

http://store.summitracing.com/partdetail.asp?autofilter=1&part=SUM%2DG2870&N=700+115&autoview=sku

I have tapped into the trigger signal to one set of points, thinking that with the wasted spark ignition I would get the right number of pulses per revolution. With it reading 1/2 the correct RPM I thought about connecting it to both trigger wires (the blue and the yellow) to double the pulses going to the tach. I'm worried that if those wires become common both coils will see both the 1,4 and 2,3 pulses from the dyna. That could be a problem. Is there a way around this?

I know there are some more expensive bike-specific tachs out there. Are those wired different internally? I'd like to get this thing working correctly if I can, but it might be a lost cause. It seems so wrong to have a 400F singing and see only 4,000 RPM.

Thanks.

TwoTired · « **Reply #1 on:** March 29, 2008, 12:22:50 AM »

The sohc4 ignition uses a wasted spark setup. So, each cylinder fires on each revolution. The point's or dyna triggers provide one 12 V pulse per revolution of the crankshaft. 1000 pulses = 1000RPM.

Automotive 4 cylinder engines usually have a distributor and it provides 4 pulses to a common coil per 2 revolutions of the crankshaft. When the unit counts 2000 pulses it indicates 1000 RPM.

The sohc4 trigger gives 1000 pulses per 1000 RPM, so your unit displays 500RPM, since it is looking for twice as many pulses.

You cannot connect the blue and yellow wires together and expect he engine to run properly. I don't know the on time of the Dyna switches when it is providing a ground path to energize the coils. If it were still points, the coils would never fire since one set of points is always closed, and you would get no trigger. The dyna may have a shorter on-time duration, which may get you more pulses to count, but then both coils would fire together, and only fire at the right time, 1/2 the time. Without a running engine, your tach will only operate while you electric start or use the kick starter. Which probably isn't what you are after. $:-\$

If we make the assumption that the tach you have is counting the rising edge of the trigger pulse. There may be an opportunity to make another pulse from the falling edge. (It has to happen before the next rise!)
There is such a thing as a pulse doubler. I've made them in the past for other circuits. Such a pulse doubler would then be placed between the tach and the trigger source signal. Or, a device can be made that generates a pulse from each trigger source of the SOHC4 and combines them into one output. Again it would be a device the was wired between the trigger sources and the tach you've purchased.
I don't know if there are already commercial devices to provide the function you need in the marketplace. But, if you can find a unit that converts an 8 Cylinder tach for use on 4 cylinders, it should work to convert a 4 Cylinder tach for use with the SOHC4 trigger.

Of course, a tach made for the SOHC4 ignition would count 1000 pulses and display 1000 RPM.

Does this help your understanding? (Sorry, I don't have a ready solution.)

Cheers,

Steve F · « **Reply #2 on:** March 29, 2008, 02:37:31 AM »

Don't know if this would work, but it would be a cheap experiment to try. Go to your local Radio Shack and get a couple of diodes, the small epoxy type should work, and place them in the circuit as shown in the attached drawing. Pay attention to the polarity when instaling them. All of this is on the assumption that the tach is looking for a "low" signal, which normally the points would supply. It's worth a try. (shrug)

troppo · « **Reply #3 on:** March 29, 2008, 02:50:01 AM »

If this works steve, you could have solved a lot of hassles for a lot of blokes...
Copied and saved for the future
Cheers
Troppo

FunJimmy · « **Reply #4 on:** March 29, 2008, 07:55:00 AM »

I upgraded the ignition in my Buell with a fancy Dyna programmable unit a couple of years ago. Buell factory ignitions, fire both cylinders together, a phase called dual fire.
Dual fire ignitions are very simply and cost effective as it allows the manufacturer to use one dual post coil to fire two plugs instead of requiring two coils. Similarly Honda has used 2 coils to fire 4 plugs. The theory with Buell’s is that when the front cylinder fires at TDC on the compression stroke, the rear cylinder is simultaneously fired on or near the exhaust stroke and vise versa.

That fancy Dyna programmable ignition can be installed and wired to two separate coils and will operate in single fire mode. Single fire mode fires each cylinder on the compression stroke only. That’s half the triggers than dual fire mode and the tach required a signal converter to be installed in the trigger line to correct the inaccurate reading. The little electronic converted is available from Dyna direct and could be a solution for your reading error.

Worth a try.

dusterdude · « **Reply #5 on:** March 29, 2008, 08:25:40 AM »

he needs to have the dyna 2000 to run single fire

GammaFlat · « **Reply #6 on:** March 29, 2008, 08:39:42 AM »

Quote from: Steve F on March 29, 2008, 02:37:31 AM

Don't know if this would work, but it would be a cheap experiment to try. Go to your local Radio Shack and get a couple of diodes, the small epoxy type should work, and place them in the circuit as shown in the attached drawing. Pay attention to the polarity when instaling them. All of this is on the assumption that the tach is looking for a "low" signal, which normally the points would supply. It's worth a try. (shrug)

I'm not an electrician but that looks like a very elegant solution Steve.

FunJimmy · « **Reply #7 on:** March 29, 2008, 08:55:11 AM »

Quote from: dusterdude on March 29, 2008, 08:25:40 AM

he needs to have the dyna 2000 to run single fire

Just sighting an example where an ignition change required a signal modifier to correct the tach reading.
I don't believe converting the SOHC4 to single fire was what I suggested either.
There are already commercially available tach adapters from the same manufacturer as his ignition.
Whether they will correct the error or not, I don’t know, but it’s worth exploring.

FJ

TwoTired · « **Reply #8 on:** March 29, 2008, 11:07:25 AM »

I see that Dyna offers tach adapters. http://www.dynaonline.com/english/dyna_tach.htm
Unfortunately, they don't mention any tech info on the site. (One of my biggest beefs with Dyna is that they require Faith to have any confidence in their products.)

However, you might call them, try to get hold of a technocrat, and see if they can explain the function of the three models they offer.

I don't think the diode solution is going to work. A lot depends how how the tach actually interprets the incoming signal. An internal schematic would certainly help.
Anyway, the diodes will need to withstand the back emf from the coil's collapsing field (300-500V?). So the PIV need to be, say 1000V. (guessing)

The diodes will also need a .7V voltage differential across them and a little bit of current in order to conduct a signal. I doubt the tach (capacitively coupled?) actually consumes much, if any, current from the points/coil circuit and without some current flow, the diodes won't conduct and turn on/off. Don't know what's in the tach, so I can't say for sure.

Cheers,

tsflstb · « **Reply #9 on:** March 29, 2008, 11:14:17 AM »

Thanks for the replies. I have a couple of diodes and was thinking of trying something like Steve drew up.

This is what I have:
http://www.radioshack.com/product/index.jsp?productId=2049725&cp=&sr=1&origkw=zener+diode&kw=zener+diode&parentPage=search

I can solder these up real quick and see what happens. My biggest fear is burning up the Dyna or my coils. Is there any remote chance of that happening?

I also found this "frequency doubler" circuit online, but have to admit I have no clue where to start with it. Is this what you were referencing Two Tired? Maybe this is the like the widget that Dyna sells.

http://www.maxim-ic.com/appnotes.cfm/appnote_number/3327
edit...saw your post TT, I guess my 12V diodes aren't up to the task.

Steve F · « **Reply #10 on:** March 29, 2008, 12:03:42 PM »

Quote from: tsflstb on March 29, 2008, 11:14:17 AM

Thanks for the replies. I have a couple of diodes and was thinking of trying something like Steve drew up.

This is what I have:
http://www.radioshack.com/product/index.jsp?productId=2049725&cp=&sr=1&origkw=zener+diode&kw=zener+diode&parentPage=search

I can solder these up real quick and see what happens. My biggest fear is burning up the Dyna or my coils. Is there any remote chance of that happening?

I also found this "frequency doubler" circuit online, but have to admit I have no clue where to start with it. Is this what you were referencing Two Tired? Maybe this is the like the widget that Dyna sells.

http://www.maxim-ic.com/appnotes.cfm/appnote_number/3327
edit...saw your post TT, I guess my 12V diodes aren't up to the task.

I think that the worst things that will happen: the tach won't work or if you reverse there sholdn't be any ill effects.

DarkRider · « **Reply #11 on:** March 29, 2008, 12:27:41 PM »

I know Sunpro makes a Tach that reads 2,4,6,8 cyls...you may need to look for something like that. I remember encountering a very simular problem with my old Cavalier RS with the 4 cyl. It has the same sort of coil scheme as an SOHC Honda. Regular 4 cyl tachs would only read half the signal..I actually salvaged my tach from my car for later use on a SOHC project.

TwoTired · « **Reply #12 on:** March 29, 2008, 05:13:26 PM »

Quote from: tsflstb on March 29, 2008, 11:14:17 AM

This is what I have:
http://www.radioshack.com/product/index.jsp?productId=2049725&cp=&sr=1&origkw=zener+diode&kw=zener+diode&parentPage=search

A zener diode is a special type of diode that doesn't conduct until it's rated voltage is met. In the case you refer to, that's 12 V.
I think what Steve was suggesting was a blocking diode. It will conduct with a .7 V differential.

Quote from: tsflstb on March 29, 2008, 11:14:17 AM

I can solder these up real quick and see what happens. My biggest fear is burning up the Dyna or my coils. Is there any remote chance of that happening?

If the back emf pulses fail the diodes open, there should not be an issue, If the diodes fail shorted, it's like they weren't there at all, and just a wire was used, shorting the dyna outputs together. I don't know enough about the Dyna output circuitry to know exactly what it is protected against. My guess is that with it's two outputs shorted together, the internal switches would just take turns drawing power through both coils. If you have 5 ohm coils the parallel resistance would then be 2.5 ohms. The dyna might survive this. However, if you have 3 ohm coils, the shorted together parallel resistance would be 1.5 ohms, which is more likely to stress the Dyna switch transistors. I think there is risk, but I can't quantify it without more details.

Quote from: tsflstb on March 29, 2008, 11:14:17 AM

I also found this "frequency doubler" circuit online, but have to admit I have no clue where to start with it. Is this what you were referencing Two Tired? Maybe this is the like the widget that Dyna sells.

http://www.maxim-ic.com/appnotes.cfm/appnote_number/3327
edit...saw your post TT, I guess my 12V diodes aren't up to the task,

The frequency doubler I envision would behave as that one. But, it would have to operate at 12-15V and be able to withstand the back EMF pulse voltage from the coils (300-500V est.) without frying.

You have a Dyna and therefore are a customer. Call them up or email them and ask them for a solution. Maybe their $21 tach adapters do what you need?

Cheers,

Cheers,

tsflstb · « **Reply #13 on:** April 05, 2008, 09:49:52 PM »

I took Jimmy and TwoTired’s advice and called Dyna’s tech support. They were really helpful. I talked to a guy about the T-101 tach adapter they sell for $21. He explained it was just a couple of diodes and resistors and assured me it would fix my problem. Then, maybe feeling guilty about charging that much for the hardware involved, he sent it to me for free:

I didn’t cut the heat shrink to see what exact parts they used, but it somebody really needs to know I will. Anyway, I spliced the ends into both coils’ trigger signals and it starts and runs like it should, plus I get to watch the fun needle sweep all the way up to 10K RPM now. I’m glad I got this sorted as I had invested a lot of hacksaw and hand file time on the top clamp to mount the tach. So in short, the $33 tach works well with a $120 Dyna-S and a $21 adapter.

FunJimmy · « **Reply #14 on:** April 05, 2008, 10:18:36 PM »

Wow, that tach and triple setup looks awesome.
You did a fantastic job of fitting it all together.

Glad you fould a resolution to the tach signal problem.

FJ

TwoTired · « **Reply #15 on:** April 06, 2008, 12:47:16 AM »

Ain't it great when a plan comes together? And, a low cost solution to boot!

Nice reference to Dyna's customer support, too!

Cheers,

smccloud · « **Reply #16 on:** April 06, 2008, 07:57:46 AM »

Quote from: tsflstb on April 05, 2008, 09:49:52 PM

I took Jimmy and TwoTired’s advice and called Dyna’s tech support. They were really helpful. I talked to a guy about the T-101 tach adapter they sell for $21. He explained it was just a couple of diodes and resistors and assured me it would fix my problem. Then, maybe feeling guilty about charging that much for the hardware involved, he sent it to me for free:

I didn’t cut the heat shrink to see what exact parts they used, but it somebody really needs to know I will. Anyway, I spliced the ends into both coils’ trigger signals and it starts and runs like it should, plus I get to watch the fun needle sweep all the way up to 10K RPM now. I’m glad I got this sorted as I had invested a lot of hacksaw and hand file time on the top clamp to mount the tach. So in short, the $33 tach works well with a $120 Dyna-S and a $21 adapter.

hate to do this, but i would love to know what parts it uses. my tach has issues (i.e. starts jumping all over at around 5000) and i am thinking of dropping a cheap auto tach on it until i can figure out the issue with the factory tach. i have a hondaman conversion box right now, so i have somethign similar to a dyna ignition system.

Kafes4ever · « **Reply #17 on:** May 22, 2008, 09:13:49 AM »

Hey tsflstb:

This is the solution I've been in search of for some time! Can you do me the immense favor of cutting into the shrink wrap sheath and note the parts underneath? I, and certainly many other CB'ers, would be forever grateful.

This is exactly the purpose and value of this SOHC forum.

Thanks, JP

tsflstb · « **Reply #18 on:** May 22, 2008, 09:45:19 AM »

Sure. I'm covered up with a few projects at home and about to start travelling, so it may be several days but I'll get to it.

I'm pretty sure it's just as Steve D describes - connect both trigger wires to the tach with a couple of diodes to keep the signals from jumping to the wrong coil. I experimented with my own using zenier diodes, which didn't work. TwoTired informed me they were the wrong kind. Regular blocking diodes would be the ones to use.

If you have a Dyna ignition, their tech support guy was really helpful. He sent me this thing for free, so I never attempted my own fix. He might just give you the parts list (or send you one) before I can get to it.

Kafes4ever · « **Reply #19 on:** May 22, 2008, 02:47:35 PM »

tsflstb:

Hold up man, I've got one coming!

I called the tech line @ Dynatek (1-800-928-3962) and talked to Angel. He was extremely helpful and offered to send a Dynatek T-101 tach adapter unit out to me... free of charge too! This is service you just don't see much anymore. These guys are great. Thanks for all the help I got from this SOHC forum. I'll report the results here when I get this installed and running.

Muchas Gracias! JP

tsflstb · « **Reply #20 on:** May 23, 2008, 08:54:01 PM »

Good to hear. I'm pretty impressed with Dynatek's product and service. I may actually put their sticker somewhere on my bike instead of on the toolbox.

I didn't realize smccloud posted the same request a while back. Didn't mean to ingore you, I just lost it in the big quoted section. Maybe if you can dissect the tach adapter before you mount it up it would help him too. Good luck with the tach.

smccloud · « **Reply #21 on:** May 23, 2008, 09:52:26 PM »

Quote from: tsflstb on May 23, 2008, 08:54:01 PM

Good to hear. I'm pretty impressed with Dynatek's product and service. I may actually put their sticker somewhere on my bike instead of on the toolbox.

I didn't realize smccloud posted the same request a while back. Didn't mean to ingore you, I just lost it in the big quoted section. Maybe if you can dissect the tach adapter before you mount it up it would help him too. Good luck with the tach.

no big deal, gotta come up with the money for an electronic tach first. and for some reason, it seems to be getting better with riding this summer. it does still suck when it jumps between 7000 and 8000 when you are riding hard.

smccloud · « **Reply #22 on:** July 22, 2008, 08:22:29 AM »

Anyone know what value the resistors in the Dyna adapter are yet?

tsflstb · « **Reply #23 on:** July 22, 2008, 01:12:37 PM »

I can put an ohm meter on that adaptor when I have a chance. I'm in the process of moving and won't get to the bike for a couple of weeks.

smccloud · « **Reply #24 on:** July 22, 2008, 02:49:24 PM »

Quote from: tsflstb on July 22, 2008, 01:12:37 PM

I can put an ohm meter on that adaptor when I have a chance. I'm in the process of moving and won't get to the bike for a couple of weeks.

i have my new tach on the way now, so as soon as you can will be great

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Author Topic: coil trigger signal and electronic tach (Read 20597 times)

troppo

Kafes4ever

Kafes4ever