I was trying to think of something along those lines, but my hobby level experience left me blind. It seemed possible, but outside of my experience.

Now I'm curious enough to set up some equipment tomorrow and scope things out. I have a truck with a HEI distributor I can tap into the coil connection and get a waveform to go off of. Granted it's not going to be the same as the OPs engine and probably a bit higher voltage wise, but it will give some base line idea.

One question is if the terminal used for the tachometer connection has a voltage spike great enough to flash a neon tube, like an NE-2 neon bulb.

 

Here is what I came up with...



I'm still getting the hang of using this thing so I missed the 10x setting to automatically do the math for the 10x setting on the probe. What I ended up with was at least 250V for the main spike which is pretty close to what I found online in various videos. This video claims around 300V and a little less noisy waveform. Since the HEI coil is a different construction than a standard coil I expected things to be a bit different.

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One question is if the terminal used for the tachometer connection has a voltage spike great enough to flash a neon tube, like an NE-2 neon bulb.

I didn't think about it when I made that comment, but if you connect to the tach connection on the cap itself then yes because it is connected to the (-) side of the coil. If you connect to the REF output of a five pin module then it's the waveform of the VR pickup which in this case would be useless.

 

OK, that 300 volt spike will even allow a series resistor and still flash a neon bulb. That would be perfect to trigger a phototransistor to toggle a FF to blank every other ignition pulse. At least, it will be worth the effort to see if the neon will actually flash.

 

The engine has a conventional ignition system with sparks distributor and for intents and purposes conventional old-skool points.

Would've thought the tacho would both be tolerant to signal spikes and work with a sqaure wave, but the output from CD4013 would be sqaure wave anyway?

 

Certainly the outputs of a CD4013 will be a square wave. But also, my most recent suggestion does not involve feeding that square wave to the tachometer, but rather using that square wave to "switch-off" alternate coil pulses fed to the tach. I have not worked out yet how best that could be done.

 

Would've thought the tacho would both be tolerant to signal spikes and work with a sqaure wave, but the output from CD4013 would be sqaure wave anyway?

Typically it's the spikes that trigger these old time tachometers. It may be possible a square wave if the tack is new enough, but that is just a guess.

 

Not to disprespect or criticise anyone on this forum but I thought the answers would be a lot more clear cut with more concensus of opinions. So in this case I decided not to make something myself but to buy something that claims to do the job and be purpose designed. I bought this item from Ebay https://www.ebay.co.uk/itm/284440826701 and I am confident it will work. But I do think it a bit of a shame that people with our common interest (electronics is certainly one of my interests) didn't come together to solve which seems at least on face value to be a very simple question to ask.. I cannot think of any slightly involved electronics that would be much simpler than this to be honest but still the outcome wasn't great. I was doing this to fulfil a purpose and solve an immediate problem or I might have delved a little deeper and built the circuits diagrams supplied by @crutschow which I still believe would most likely have worked.

I really like all your fancy oscilloscopes and equipment but do have to wonder what good it does you if you're not sure about a circuit diagram for the things I said I needed a (on face value) simple circuit to do. 'On face value' and 'simple circuit' in the context pulses / waveforms etc on the pulsing wire of an old-skool ignition coil, and any workarounds to divide such pulses, must surely be well known areas of electronics.

I am in no way an expert but have a lifetime interest in electronics and have solved quite a few problems in my time building circuits of my own design to solve/fix real world problems. It is a little underwhelming to ask a forum of experts and wonder if I'd be better off approaching the problem on my own. It would be great to see you pull together and reach a concensus and correct answer to relatively simple questions or at least bounce of each others posts - But I am afraid I am left thinking you compete against each other to show off to each other the best kit without really knowing the subject. I am fairly sure that the tach will pick up on 12v pulses and I thank people for their input, especially circuit diagrams that I believe will work, but enough doubt has been added that I would rather buy something than make something on this one. Do you talk to each other at all or do you compete with each other?

 

Not to disprespect or criticise anyone on this forum but I thought the answers would be a lot more clear cut with more concensus of opinions. So in this case I decided not to make something myself but to buy something that claims to do the job and be purpose designed. I bought this item from Ebay https://www.ebay.co.uk/itm/284440826701 and I am confident it will work. But I do think it a bit of a shame that people with our common interest (electronics is certainly one of my interests) didn't come together to solve which seems at least on face value to be a very simple question to ask.. I cannot think of any slightly involved electronics that would be much simpler than this to be honest but still the outcome wasn't great. I was doing this to fulfil a purpose and solve an immediate problem or I might have delved a little deeper and built the circuits diagrams supplied by @crutschow which I still believe would most likely have worked.

I really like all your fancy oscilloscopes and equipment but do have to wonder what good it does you if you're not sure about a circuit diagram for the things I said I needed a (on face value) simple circuit to do. 'On face value' and 'simple circuit' in the context pulses / waveforms etc on the pulsing wire of an old-skool ignition coil, and any workarounds to divide such pulses, must surely be well known areas of electronics.

I am in no way an expert but have a lifetime interest in electronics and have solved quite a few problems in my time building circuits of my own design to solve/fix real world problems. It is a little underwhelming to ask a forum of experts and wonder if I'd be better off approaching the problem on my own. It would be great to see you pull together and reach a concensus and correct answer to relatively simple questions or at least bounce of each others posts - But I am afraid I am left thinking you compete against each other to show off to each other the best kit without really knowing the subject. I am fairly sure that the tach will pick up on 12v pulses and I thank people for their input, especially circuit diagrams that I believe will work, but enough doubt has been added that I would rather buy something than make something on this one. Do you talk to each other at all or do you compete with each other?

There is a reason that is quite logical for the diversity of responses and concepts. It is because this is not just a gathering of folks with similar interests. What you get here is responses from a vast number of not only masters and engineers, but also folks with vast banks of experience, from all over the world. The total knowledge and experience vastly exceeds the "wici" site, in areas where it applies. So you are tapping in to hundreds of years of engineering experience, in addition to what a huge array of hobby experimenters have learned. So it is not that we are not certain about an answer, it is that at least in this question, there are a whole lot of answers that will work.

 

It also helps when people are willing to provide details requested like photos, diagrams, and the like. Putting a little of your own effort into the answer helps also. People will also pick their battles... there are many new threads created every day and if they feel they will be more helpful to another topic they will spend more time there.

This project is also dealing with mixing voltages and signals that can go horribly wrong, be dangerous to people and property, and cause more than an acceptable level of damage if things go wrong. There are times you are better off buying something that works then trying to create your own.

 

It also helps when people are willing to provide details requested like photos, diagrams, and the like. Putting a little of your own effort into the answer helps also. People will also pick their battles... there are many new threads created every day and if they feel they will be more helpful to another topic they will spend more time there.

This project is also dealing with mixing voltages and signals that can go horribly wrong, be dangerous to people and property, and cause more than an acceptable level of damage if things go wrong. There are times you are better off buying something that works then trying to create your own.

G.O.T.W is correct about the various signals, which is my suggestion last was using an optical trigger scheme to "delete " half of the pulses instead of counting them. That had not popped into my head earlier, until another mentioned the very noisy pulse as the breaker points open.

 

G.O.T.W is correct about the various signals, which is my suggestion last was using an optical trigger scheme to "delete " half of the pulses instead of counting them.

I like that idea myself and looked through my box of parts to see if I had anything with decent enough ratings with enough head room to make me comfortable for some experimentation, but came up short. Since this is a bit outside my realm, I would have to research and order parts, and would really never have a use for it other than tinkering it's not worth my time right now unfortunately. Maybe a good winter project, but by then it will be too late for this.

 

I like that idea myself and looked through my box of parts to see if I had anything with decent enough ratings with enough head room to make me comfortable for some experimentation, but came up short. Since this is a bit outside my realm, I would have to research and order parts, and would really never have a use for it other than tinkering it's not worth my time right now unfortunately. Maybe a good winter project, but by then it will be too late for this.

The main part would be the neon bulb to see if it can trigger off the noisy breaker points pulse. AND probably the photodiode to sense that flash of light.

 

Sorry for being harsh in my last post above.

This is the gizmo I bought https://www.ebay.co.uk/itm/284440826701

Even though I've bought the gizmo I'm still interested in circuit designs that could halve the pulses from my coil to the tacho. I think I was expecting people here to be able to come up with various designs 'off the top of their heads', scribble them on the back of a beer mat, take a photo and post it up lol, was expecting a few designs and a bit of discussion on the pros and cons of each design.

The gizmo hasn't arrived yet, it is supposedly capable of converting coil pulses from any engine to suit any tacho regardless of number of engine cylinders, so I don't believe it will use the CD4013... But still you and I may be interested in what is inside the gizmo and if I can easily get the back off it for a view inside I will do that and post pics, some here may be able to tell how it works or aspects such as whether it triggers from high voltage spikes etc.

 

Sorry for being harsh in my last post above.

This is the gizmo I bought https://www.ebay.co.uk/itm/284440826701

Even though I've bought the gizmo I'm still interested in circuit designs that could halve the pulses from my coil to the tacho. I think I was expecting people here to be able to come up with various designs 'off the top of their heads', scribble them on the back of a beer mat, take a photo and post it up lol, was expecting a few designs and a bit of discussion on the pros and cons of each design.

The gizmo hasn't arrived yet, it is supposedly capable of converting coil pulses from any engine to suit any tacho regardless of number of engine cylinders, so I don't believe it will use the CD4013... But still you and I may be interested in what is inside the gizmo and if I can easily get the back off it for a view inside I will do that and post pics, some here may be able to tell how it works or aspects such as whether it triggers from high voltage spikes etc.

I look at the photo and I see only three wires. So I am wagering that it is an amplitude clamping device applicable to any number of cylinders. So here is hoping that it is much better than what I anticipate.

 

I look at the photo and I see only three wires. So I am wagering that it is an amplitude clamping device applicable to any number of cylinders. So here is hoping that it is much better than what I anticipate.

There are clearly 4 wires shown in the picture and wiring diagram, 4 wires are mentioned in the description and it is supposedly capable of upscaling (multiplying) pulses...

 

OK, it was not clear on my screen. The photo did not show any controls that I could see. I look forward to seeing how it performs for you.I am guessing that the four wires are : common, input, output, and program.