Custom Ignition For A Citroën Mehari

The 20th century saw a great many cheap, utilitarian vehicles enter the marketplace. Cars like the Mini and the original Jeep offered low-cost, no-frills motoring. However, they were also decidedly low-tech, and not as reliable as modern cars by a long shot. The Citroën Mehari fits into this category neatly, and when [FVFILIPPETTI] grew tired of the unreliable points ignition system, he decided to build a more modern replacement.

The system is based around at ATmega328, the venerable chip many are familiar with from its starring role in the Arduino Uno. The chip tracks engine position with a magnet mounted on the flywheel combined with a hall-effect sensor, passed through an optocoupler to avoid nasty high-voltage spikes from the spark system interfering with the microcontroller. The chip then charges the ignition coil and fires it at the necessary time to ignite the air fuel mixture.

Old-school mechanical ignition systems were, if we’re honest, terrible compared to more modern solutions. This build has rewarded [FVFILIPPETTI] with a far more reliable ride, which we’re sure is very satisfying. If all this hacking has you thirsty for an automotive project of your own, dive into our primer on how to get into cars!

42 thoughts on “Custom Ignition For A Citroën Mehari

  1. “Old-school mechanical ignition systems were, if we’re honest, terrible compared to more modern solutions.”

    True, but in a third-world country where is one going to pick up an ATmega328?

    1. I imagine they would get an ATmega328 from a Developing Country….

      You should visit Argentina sometime. You may find things there can be far more advanced than your “third-world” comment portrays.

      1. Well you’ll note just what I quoted, my point can be summed up as, you work with what you have. That’s why you’ll see old-school still around even if it’s “terrible”. Third-world does have a strong make do culture. Nothing to be ashamed of.

        1. Sorry I should have been more direct, my real point was to steer folks from using the term “third-world”, a post-WW2 term to describe non-“Western” and non-communist countries, with rather negative (and sometimes racist) connotations, to instead consider using the less offensive term “Developing World” or “Developing Country/Nation” .

      2. Plus it’s Buenos Aires. Plenty of parts of Argentina are very rural, but not BA. If you need something, it’s usually just a question of how long it takes to get from Buenos Aires.

    2. There are a variety of 2CV electronic ignition replacements. I know this isn’t a hackaday answer but given the noted concern about the durability of the system, sourcing an off the shelf replacement might have been a better option.

    3. All you had to do was google for “Is Argentina a third world country” and you would’ve gotten many links explaining that it isnt.

      Fun fact, if you search the same question for America you get many links saying that the US pretty much is a third world country (lots of overfull prisons, many many family’s living below poverty line, lacking healthcare, lacking education, terrible infrastructure, etc etc)

      Think about that for a bit, and try remember that next time you want to call some place a third world country.

      1. No, Irox was the one that jumped to the Argentina third-world connection. If one pays attention to what I quoted I said in a third-world country where is one getting an ATmega328. Nothing about Argentina was even mentioned. So don’t be lecturing me about googling when most can’t even be bothered to read properly.

        1. Uhhhhh? Irox made that connection because of your post implying it, dont try to blame somebody else for your rude reaction?

          The quote doesn’t somehow make your comment about other countries? how does that logic even work? its pretty much the opposite? the quote talks about the situation for the people in the article, that live in Argentina, you then go “yea but third world country” so how is anybody supposed to interpret that as you NOT meaning to say that Argentina is a third world country?

          Honestly stop trying to talk yourself out of it, just accept this as a learning moment, calling Argentina third world country is not cool, and factually wrong, trying to talk your way out of it with some backwards logic (“pay attention & read properly” uhh what? how about you write properly if that’s apparently not what you meant?) is just sad, own up to the things you post.

          1. You must be a Democrat or other variety of leftist because they are always “reading” things into what people write or say *that they did not actually write or say*. They think they have the power to divine “hidden meanings” and “implied” nastiness that just isn’t there.

      1. (another Argie here)

        Trying to do that here and you’ll end up paying more than twice the displayed amount on Ali (or any other similar marketplace). Also forget about normal mail, you really need to use a courier service. I have packages that arrived on January 2020 still locked in customs at walking distance from home (nothing fancy, just stickers and other promo stuff from work under 100u$s).

        Back on topic, in our family we had a 2CV and 3CV. The points on one never failed on five years of very intensive use and the other had a reluctance sensor with a simple circuit to excite the coil.

        Awesome cars to delve intro wrenching.

    4. Perhaps you were thinking Mars or Saturn, here on Earth we order these by mail, there are very few places in the planet where you cannot get a tiny package delivered. As a matter of fact, it could be way easier to find an ATmega328 than an ignition system for a car made in the late 60s.

  2. Missed the now fully featured open source ecu “Speeduino”, featured here a few years ago when it was just a controller for a single cylinder go kart, now new units more powerful than others a magnitude higher price.

    1. Another pretty cheap but durable way to do this is to get a ford EDIS coil/missing tooth sensor, and then you can use any arduino, without needing external circuitrly, to read the sensor, calculate your timing table, and send that as logic-level signaling to the EDIS, which handles the high voltage high current spark production. The EDIS unit is very reliable. Automotive electronics are quite challenging for long-term reliability, so I’m pretty fond of using stuff that’s been running for 20 years and only adding as little new-possibly-not-robust tech as possible.

      1. But wasn’t EDIS product life short due to reliability problems?
        EDIS-4 lasted five or six years as a product?
        (found this

        Instead of a coil per pair of cylinders, wasn’t going to a coil per cylinder supposed to fix the reliability issue? And cut the wasted spark, and have shorter high tension cable or sit the coil right on the plug?

        What replaced EDIS and what do you think of it?

        1. EDIS lasted as long as the EEC-IV ECUs did until replaced by OBD-II compliant ECU required by new emissions regs. That’s the short lifespan really, went from carbs to injected 8051 control then OBD-II.

          The only problem I had with EDIS as installed in Fords, was that ignition wire manufacturers didn’t step up their game for the higher energy vs distributor and standard coil, so 75% of the wires on the market were crap and would flashover after a month or so. Needed NGK or Motorcraft wires to work, Bosch, Champion etc were trash. And I know they’ll cope with 7500+ RPM.. due to being “reliably” informed that X, Y, and Z would limit RPM to a max of 6,500 and therefore a rev limiter was not required… so on my lightly modded motor, I floored it in low gear one time, up a steep hill so it was actually loaded, and was alarmed to see my rev counter blow past 7500 while it was still pulling, I lifted off sharply… Then another couple of times I managed to kick it down to second (Auto) on the highway while passing and it sounded like an F1 motor for a couple of seconds before it shifted up… man that gave me palpitations too LOL. I didn’t see what revs it hit those times, due to concentrating on maneuvers, but pretty darn high up there to make F1-ish sounds. (Probably way off the fuel map and a bit lean too, I wanted to give it a bit more injector to help eventually)

          1. “Wasted spark” firing on a cylinder that’s exhausting at the same time as the companion cylinder is at the firing point of the compression stroke could help improve emissions by burning some leftover fuel.

  3. You can literally pick up a Pertronix or other brand electronic pickup to perfectly bolt in place of a points setup and
    forget having to program it. I’ve been a passenger in a Citroen mehari and it’s absolutely terrifying haha. The shifter is a bizarre slide mechanism.

  4. The mechanical ignition system of the 2CV and its derivates is extremely reliable as it was out of the factory. Nowadays issues are mostly from horrible replacement capacitors (one lasted less than 100km). Using industrial film capacitors instead brings back the reliability these vehicles are known for.
    But always good to know how to build an electronic version from scratch.

    1. This! These cars were of outstanding reliability 40 years ago. If they are no longer, something was done wrong.

      A simple measure to further increase reliability and reduce maintenance requirements is to support the timing breaker with a simple transistor/MOSFET amplifier. Once this breaker no longer switches 2 amps, but just a milliamp, its wear is reduced to like nothing. A measure which was available in the 1990s already.

      1. I found such a bypassing device (Sirius I or II) on a scrapyard, but haven’t implemented it in one of my 2CVs, yet. Will do some investigations how it works. No big board, just a Thyristor and a hand full of resistors and capacitors, reverse engineering won’t be a big deal.

  5. From where they are produced: from China.

    If globalization has one upside, then it’s this: the so-called “third world” soon isn’t going to need the “first world. “Our” smugness is pretty much unwarranted.

    Yes, first world has invented “intellectual property” to cling to the last colonial advantage it thinks it has.

    Pretty soon China is going to beat it at its own game and going to flood it with patents. Look at the numbers if you don’t believe me.

    And no, I’m not a friend of unchecked, global capitalism. I’m much less a friend of China’s authoritarian system, which (among other known cruelties) jails ten percent of the 11 million population in Xinjiang.

    But I’d like to warn that the “West”‘s “sense of superiority” is pure, decadent idiocy. We’ll wake up, eventually.

    Remember when Japan’s auto industry beat ours? Remember it was at the quality game? At that time we were cracking jokes about low quality Japanese copies of Western industry products.

    Did we learn anything back then?

    1. “When it gets down to it — talking trade balances here — once we’ve brain-drained all our technology into other countries, once things have evened out, they’re making cars in Bolivia and microwave ovens in Tadzhikistan and selling them here — once our edge in natural resources has been made irrelevant by giant Hong Kong ships and dirigibles that can ship North Dakota all the way to New Zealand for a nickel — once the Invisible Hand has taken away all those historical inequities and smeared them out into a broad global layer of what a Pakistani brickmaker would consider to be prosperity — y’know what? There’s only four things we do better than anyone else:
      microcode (software)
      high-speed pizza delivery” Snow Crash

  6. Considering that CITROËN MEHARI is so trendy in France since several years spotted by the bourgeoisie and posh circles (it’s not uncommon to see prices for used MEHARI up to 20.000€), may be you can sell them an ATmega328 ignition hack for 500 or 1.000€… ;)

    Typical scenario of MEHARI usage : take the Porsche Cayenne from Bordeaux or Paris to go to the second home by the Sea at the Cap Ferret for the week-end, and then use the MEHARI locally.

  7. Single word: maintenance. In approximately 1million miles operating an aircooled 72 superbug, I cant recall a point set failing without a performance warning. Had pertronix, hated it because couldn’t set the dwell which was pivotal in reducing the engine bog between 2 & 3rd gear.

    So: if you check the points periodically, clean and adjust the gap, apply a bit of clean lube to the cam lobes I don’t see how mechanical systems are unreliable

    1. Because you had to push them so often. maybe it was a combination of bad carbs, bad points and bad compression but older cars weren’t easy to start at all, according to my dad at least. he spent many days pushing them downhill to get up to speed. then when they didn’t fire off you had to push them uphill again.
      motorbikes could be even worse as they rarely used a battery and had a weak spark.

    2. You had to screw with them monthly to maintain gas mileage and performance, unless you didn’t care and let them spew as bad as a diesel “rolling coal” between 6 monthly dealer tuneups and just thought 7mpg was normal… and that would only be possible somewhere with a dry climate. So mess with “simple” mechanical ignition 60+ times, vs replace the plugs every 5 years/100,000 miles. Where part of the messing would have been 5 plug replacements and a dozen clean and regaps.

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