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2GCDFIS w/ TT (Transistor Trick) Write-Up (Simplified Design)

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2GCDFIS w/ TT (Transistor Trick) Write-Up (Simplified Design)

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Old 12-02-05, 11:34 AM
  #26  
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Correct...
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Old 12-16-05, 02:48 PM
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Anyone

I've been trying to get this simplified curcuit to run on the "electronics work bench" simulation program. It looks good for a while, pretty nice square wave output with a 12V sine wave input. But the curcuit crashes with the inputs and loads I've set it up with. The values I used are just a WAG ;-)

What are the inputs? Do the J109's sink on fire?

What reasonable load should the Out of this simplified curcuit see?

I've just been putting the O-scope on the output which is tied to gnd through a 1k resister. Maybe I should be putting a 10 -100 K resister on the output.

Anyway. Great fun. Can anyone steer me straight?

TIA

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Old 12-16-05, 03:19 PM
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The J-109 sinks during firing. It is basically an open collector. Take a look at the big TT thread. I have a couple SPICE layouts shown. I simulated the J-109 with a NPN transistor. I then fed the base of the transistor with either a sine or square wave.

For the output, the 2nd gen coil has about a 1k input resistance (something like 1.1 k or something). That is why I had to add the second transistor in the circuit (one before the output). The low input resistance cased the 5v high to get pulled down to about 2.5v or so without the follower (1k pull-up resistor and the input resistance of the 2nd gen coil acting as a voltage divider). The second transistor is setup as a voltage follower. The output equals the input, but about 0.6 to 0.7 volts lower. The output pulse this way is limited to ~4.3 v or so.

If you have any other questions, let me know.

Kent
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Old 12-16-05, 03:42 PM
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Thanks Kent.

I'll give the model another try with the values you suggest.

The TT thread is so big! I should sort on your contributions for the layout.

Can you see any real frequency limit with this simplified layout? I model at 100 and 350 hz. Seems "real world" enough.

Fun and stuff

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Old 12-16-05, 03:47 PM
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Oopps I should have included this ??

Kent

When you say "For the output, the 2nd gen coil has about a 1k input resistance (something like 1.1 k or something)". Are you saying the 2nd gen "ignitor pack"?

Coil resistance is usually very low. (But I don't have an example of the 2nd gen double ended leading coil to measure)

Thanks

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Old 12-16-05, 03:55 PM
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Yeah, it's pretty huge. What you want is within the first few pages, though. Shouldn't be too hard to track down. I am not sure if I have one posted with the voltage follower or not. That was added afterword as I didn't know that the 2nd gen coil had such a low input resistance at the time. If you can't find what you need, let me know. I should be able to come up with something.

Those frequencies are fine. I looked at like ~23Hz to 333Hz. The 20 something Hz is idle, the 333Hz is like 10,000rpm. I don't think you will see any frequency related problems. I bet this could run into the MHz range without problem.

The auto-switching and fixed pulsewidth versions have a limit of ~14,000rpm or so. This is because the pulse is set to 2.1 or 2.2 ms. Once the pulses happen faster than that, the circuit will not retrigger.

What kind of stuff are you trying to model? Just for fun? A class? Anyway, looks like you are headed in the right direction wiih the modeling.

Kent

Edit: Yes. I mean the pack (input to the ignitor to be exact).

Last edited by gsl-se addict; 12-16-05 at 03:57 PM.
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Old 12-16-05, 07:42 PM
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i have done that to my car as soon as i got it but i didnt know some of yall wanted to do that too i have the same set up in mine DF i like it
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Old 12-17-05, 02:34 AM
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EWB enjoys crashing with cryptic timestep errors, especially when assignements are closing on their due dates. what version EWB are you using, and will you post the .ewb file when you're finished?
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Old 12-17-05, 02:58 AM
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I don't have much experience with EWB. Do you have to use it for your project or can you use SPICE or something else? Maybe try some different transistor models. Doesn't matter much what you use, just needs to be NPN. I can help you guys out where I can. You can send me screen shots of the layout and/or the error and maybe I can figure out something to try.

Good luck.

Kent
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Old 12-17-05, 09:36 AM
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Kent - I have one of the TTs that you built and shipped just before moving to France - were those autoswitching (type 4)?
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Old 12-17-05, 09:44 AM
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Yes. That is correct.
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Old 12-21-05, 04:40 PM
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Kent and all

Sorry to drop out of a conversation.

Regarding the use of the EWB, it's just for fun. My son snagged a copy somewhere. (2nd year eng student at Northeastern Univ.) Me, I'm just trying to get my mind around some electronics for the fun of it. optical engineer by profession, thin films. Electronics is just a fact of life.

If I knew what the h---- these circuts were supposed to do, I guess I could calculate the results. But since I know neither the source nor the load..... The software makes it kind of fun, and is a pleasant enough diversion with morning coffee.

I have this little project with the -7 ( I need to get the double ended" leading coil. I have obtained the 2nd gen trailing coils and ignitor pack, but they are bulky and probably shouldn't be fired together though I'm not sure on that)

The other project is similar. Ignition modules for a Moto Morini Motorcycle. Replacement parts are hard to get, and it seems that home made units are part of that culture.

It's all just for fun

I need to refine the model. Perhaps I'll try the later revision of EWB.

I don't really know that application either.

More as I get to it

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Old 12-31-05, 01:22 PM
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Am I correct in deducing that this write-up is only good to 10K rpms? Reason I ask is because this is going on a 13B j-bridge, and I'll likely see 12.5K frequently...
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Old 12-31-05, 02:03 PM
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No, it will actually do much higher than that. The circuit can handle well beyond any rpm the engine can do. I know that this circuit with the 2nd gen coil can handle 15k RPM without problem based on bench testing I did. One thing that could be an issue is that this design uses the 1st gen dizzy/ignitor to set the pulsewidth. According to Jeff20B's measurements, the 1st gen dizzy/ignitor drops off the pulsewidth above 4000 rpm. I think the auto-switching version would be better, especially for high RPM use. It forces the pulsewidth to stay above a preset limit. This means that even if the 1st gen dizzy/ignitor drops off at high RPM, the spark from the TT and 2nd gen coil will stay strong.

I hope to start the group buy for a kit to build the auto-switching unit. There will likely be assembled versions available as well. Just waiting approval from Ryan to start the GB.

The only thing is that since the auto-switching version has a fixed pulsewidth in the upper RPM range, the RPM is limited by this PW. With the value that I used (2.2 ms), the RPM is limited to around 13.6k RPM. This is because above this value, the engine will be triggering the circuit in a shorter time than the pulse is. This is probably fine as is for you, but you could give yourself a little more cushion by reducing this pulsewidth. It just means switching 1 resistor. You could set it to say 2ms to give a limit of 15k.
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Old 12-31-05, 05:09 PM
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I just bought everything today.... $14.39 As soon as I can get a carburetor for my car, I'll let you know how this works!
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Old 01-25-06, 08:16 AM
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So I could substitute this resistor to affectively use the TT circuit to rev limit my engine.

I think I saw this posted by you somewhere, but isn't there someway to compute this resistance basded on an rpm target ? Also, which resistor is it in the circuit posted here ?

I've got my parts and I'm building it this week and thinking of rev limiting my stockport 12a to 8k or so. Besides its a fun project. I may modify it so I can use a small pot for the resistor to adjust it.
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Old 01-25-06, 08:36 AM
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This version of the circuit has no way of controlling RPM. All it does is convert the 12v signal from the J-109 to a signal the 2nd gen ignitor can use. One thing is the couple ignitor failures reported. This design and the auto-switcher from the last GB has the same problem. The J-109 uses too long of a pulse at lower RPM. I do recommend that if this design is used, an additonal ballast resistor should probably be used. I don't know the ideal value, but probably 1 Ohm with a power rating of 10W or better should do. This would be placed on the 12v power wire to the 2nd gen coil. This will limit the current and should help the 2nd gen ignitor last. The only problem that I see is that performance may be decreased, especially in the upper RPM because of the resistor.

It would be possible to add a rev limiter. One way would be to use a low-pass filter to cut the signal above a certain point. However, this wouldn't give a sharp cut-off.

Another possibility is to use something like the MC14538B listed in the other circuit. If you set the cap/resistance for a pulse equal to the max RPM you want, the circuit will not output anything above that. It is because the output pulse is longer than the input one. The circuit won't retrigger during the output pulse. You could also wire something with a 555 timer chip. I would have to think of how you could wire this in to get a rev limiter.

As you know, I am doing kits for the new auto-switching unit. It may be the easier way to go. However, you could just build this simple version, then add the additional stuff later to improve.

Good luck. Let me know if you have any questions.

Kent
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Old 01-25-06, 08:39 AM
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I found this post that seems to answer my question:

https://www.rx7club.com/showthread.p...24#post5196524

Looks like I can substitute the 22K resister for a 40K to get a 4ms pulse width but I'm still fuzzy on computing the rpm target.
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Old 01-25-06, 09:02 AM
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That version has the min and max pulsewidths. The min set how low the pulse can be. If we use the 22k, the min pulse is 2.2ms. With it this way, if the J-109 puts in say a 1.5ms pulse, the pulse to the 2nd gen ignitor will still be 2.2ms. The 40k in that circuit just does the other end of the spectrum. If the J-109 puts out say a 6.5ms pulse, the output pulse to the 2nd gen ignitor will be limited to 4ms.

Now, the 2.2ms pulse does have an upper limit RPM associated with it (About 13,000 RPM). If you increase the value of the pulse, you could drop to say 8000 RPM limit giving a rev limiter in effect. The problem is that you will be pushing the ignitor hard near redline (the duty cycle will approach 100% as you approach 8000 rpm).

I'll take a look at it to see if there is a better way of doing it.
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Old 01-25-06, 09:57 AM
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Kent, no big deal it was just an idea. Thanks for pointing out the extra ballast resister tho, I will definitely put that in when I build this. I could build the other circuit but I'm not that worried about getting the max performance across the entire rev range and this is a KISS design which makes it more attractive to me.
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Old 04-14-10, 07:42 AM
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Guys, would there be a way of doing this on one of the early S1 contact breaker points dizzy's, converting the output into your square wave form 5v pulses for a 2nd gen leading coil / igniter. Any advice would be appreciated, if it's a possibility I'll research it more.. Thanks

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Old 04-14-10, 04:22 PM
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Originally Posted by gsl-se addict View Post
This write-up is for number 3 on that list. The group buy will be for number 4. The trailing doesn't matter much. You won't need the trailing fixed before doing this mod.

For the coil, you will need a 2nd gen leading coil w/ ignitor (The one shown as P on Mazdatrix). Usually they come this way (ignitor w/ coil). It can be off of any year 2nd gen ('86-'91) and can be off of either a TII car or an NA. It doesn't matter. E-bay or the 2nd gen for sale section on here are probably the best place to pick one up. You can also check with your local wrecking yards.

Kent,

I have a TT box that I bought from a forum member about 2 years ago that I never hooked up. How can I tell if it is the version 4 autoswitch TT? Kentetsu, did I buy this from you? I can't remember.
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Old 11-15-10, 11:07 PM
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where can i buy one of these TT boxes?
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Old 11-16-10, 12:39 PM
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Originally Posted by mjm4jc View Post
Kent,

I have a TT box that I bought from a forum member about 2 years ago that I never hooked up. How can I tell if it is the version 4 autoswitch TT? Kentetsu, did I buy this from you? I can't remember.
Sorry, I missed this post last spring.

Yes, I believe you did purchase that from me. It is the one with the switch, so maybe version 3?

I regret having sold that now, though. That was the best working one that I've tried, other than the burning up the coils issue. lol. But it sure did make some monstrous power!

I've actually been running stock ignition for the last year, simply because I haven't had the time to throw anything else together (and I need to buy another coil pack too). I'll have to address this in the spring though, because I really do miss that power...
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Old 11-16-10, 01:53 PM
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Originally Posted by Kentetsu View Post
Sorry, I missed this post last spring.

Yes, I believe you did purchase that from me. It is the one with the switch, so maybe version 3?

I regret having sold that now, though. That was the best working one that I've tried, other than the burning up the coils issue. lol. But it sure did make some monstrous power!

I've actually been running stock ignition for the last year, simply because I haven't had the time to throw anything else together (and I need to buy another coil pack too). I'll have to address this in the spring though, because I really do miss that power...
You should give TFIDFIS a try and see if the power is comparable to the TT trick. If nothing else the TFIDFIS setup wouldn't burn out on you, but would be an improvement over stock ignition.

https://www.rx7club.com/1st-generation-specific-1979-1985-18/tfidfis-894669/

I've been reading thru all the ignition threads and I think I'm going to do TFIDFIS on Gus.

Jamie
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