A Tidy Little OBD Display For Your Car

It’s likely that many readers will have an OBD dongle through which they can peer into the inner workings of their car, but the chances are that most of us will have restricted our curiosity to the Bluetooth or USB interface it was supplied with. Not [Frederico Souza Sant’ana] though, because he’s modified his OBD dongle to expose the serial lines between its ELM327 OBD chip and its Bluetooth chip. These go to an Arduino, which powers a small information display to supplement the car’s dashboard. This can display a range of readings as can be seen in the video below the break, he has it monitoring the battery, the various temperatures in the engine bay, and the ignition parameters.

All the software and hardware details can be found in a GitHub repository. In hardware terms it’s a surprisingly simple unit, but it serves to remind us that OBD sniffer dongles are more versatile than we might at first imagine, and good for a bit more than hooking up our smartphones via Bluetooth. If OBD is something you’d like to visit in more depth, in the past we’ve featured an open-source OBD interface, and a retrospective look at the protocol.

43 thoughts on “A Tidy Little OBD Display For Your Car

      1. Why tie up your smartphone? I might also add that in every state in USA, there are fines and penalties for distracted driving. It’s illegal to operate a mobile device the vehicle is in motion without a hands free device in operation. You completely missed the point of this project. No cellphones are operated while the vehicle is in motion, making this device completely legal and safe to operate.

          1. However if you crash whilst doing so… you’re at fault for negligent driving. So you still have to be careful of not being overly distracted…

    1. OMG, I hope no one tried to read that thing while driving….

      I do love it when people state 11 years ago was a long time for this field.

      What’s old is new again is new again is new again.

  1. I bought one of the generic bluetooth ODB II dongles a couple of years ago just to link to my Android smartphone and I ended up using it a couple of times and then left unplugged since.
    They are sort of fun and interesting but I don’t see where the real use for them comes. This article sort of highlights it, it’s a really technically interesting build but… where is the long term point?

    1. I’m thinking it depends on the features a car comes with…
      This display could be useful displaying Intake Manifold Temperature as “outside temperature” on a car that doesn’t have such a display.
      Or “engine temp” for a car that only has a red/green/blue LED.

    2. If you have check engine light on it tells you what to fix and clears codes when done. They are highly useful and effective everyday driving you really don’t need unless you want to watch vitals coolant temp,battery voltage, evap readings, etc but long term it’s what mechanic does when you take care to him put the one on it and fix problem it tells him

      1. It doesn’t tell you what to fix. Codes are a symptom, not the actual problem itself. While sometimes the code will point to the exact problem, replacing any part on just a code without proper diagnosis is just guess work.

    3. All of the gauges in your car are fake. They don’t move because “people” are dumb and don’t expect anything on the dash but the speedometer to move. They would go to the dealer and complain “this gauge moves when I push the gas, and this gauge moves when it’s hot out or I turn on the A/C. Something’s wrong with the car!”

      Car makers couldn’t figure out how to explain gauges to “people”, but knew that gauges are perceived as “premium” and had to remain, so they modified them so they don’t move. Some cars don’t even have sensors for the gauges in the dash! (For example, the Mazda RX-8 has an oil pressure gauge but no pressure sensor!. The gauge is 100% fraudulent.)

      OBDII on your phone via a bluetooth dongle is the quickest, cheapest way to get useful values for things like oil pressure (if there is a sensor) and engine coolant temperature. It’s also the quickest and cheapest way to monitor long-term and short-term fuel trims (for tuning), engine load, closed- or open-loop control, transmission temperature (in some cars), emissions test readiness, fault codes, fuel consumption, and many, many other interesting things.

      1. On all three occasions over the decades that I have seen a drastic loss of oil pressure on the gauge, and investigated, it was the oil pressure sender itself that had sprung a large leak. So I tend to regard those as not very essential. Unless the dark stripe behind you leaving from the qwik-e-lube isn’t enough clue they didn’t tighten your filter or drain plug right.

        1. Oil and temp sensors are vital to learn when your car is having low oil pressure which can be caused by several things, including leaks. Temp sensor will tell you when engine temperature is going north, if you pay attention you may save the engine….yes, sensors may leak or go bad, but believe me, it’s better to have them sitting there for years just telling you all is ok!

      2. The “gauges are fake” is highly dependent on what manufacturer you bought your car from.
        I have seen some where the gauge snaps to a “good” position as soon as the engine is running, and stays there until you turn off the key… And ridiculed the vehicle for it as well.

        There are others which still have functional indicators.
        The VW that the article is about appears to be a mk4 based on the gauge layout. Based on that assumption, and my experience with those years of cars, I have seen only one gauge that is spoofed, and that is just damping the motion of the temp gauge when it’s near 190°F. Anything from ~175 to 205 will show as a steady 190°, before it starts to swing up from there if the engine is overheating.
        Idiot light for oil pressure, driven by an actual pressure sensor.
        No indicator for the Intake temp, intake pressure (on the turbocharged diesel I have), no MAF indicator…

        Hooking up a ELM327 dongle and pairing it with the Torque app, I have nearly instant access to any of the information that the computer collects, and a few more that can be calculated from the provided information.

        That said, there are definitely parts of the OBD-II data stream that aren’t accessible with the generic code reader dongles.
        If I really want to know what is going on in my ECU, I have to plug in a VCDS cable and load the matching software. That gives me access to adjusting, calibrating, and live data stream for many functions that are not part of the OBD-II protocol.
        (Then again, who cares the exact status of all five cruise control input switches, or the behavior of the keyless entry remote in regard to power windows, when you just want to know how your engine is running?)

      3. “All of the gauges in your car are fake.”

        I had a TT whose coolant temperature would never reach 90 degrees, it would stay at around 70, as shown on the gauge. At one point the thermostat failed and was replaced. The gauge would now go up to 90 and I also noticed the heating worked a lot better.

      4. Before the OBD I days, rumor has it that Ford dealers would have customers complain that oil pressure was lower when the engine was warm, and to fix it. That’s why every Ford car and truck that have oil pressure gauges, since the OBD I days, have fake gauges, and just an oil pressure switch that turns on with as little as 5psi of oil pressure, and showing normal on the gauge (slightly higher than center)

        On my 2006 Ford F-150 5.4L, I installed an AutoMeter oil pressure sensor (and gauge) on a T with the oil pressure switch. Normal when cold is 70-75psi, and 25-30psi when warmed all the way up

        1. Both my 99 and 02 Silverado had functioning oil pressure gauges. They’d do the same – higher when cold, lower when hot. Rev the engine and it would go up. Same with battery voltage and engine temp.

      5. “Synthetic” is not the same as “fake”,
        Some of the information might be “massaged” or derived from other sources, but that doesn’t mean the information is meaningless or false.

        1. Yes, yes it is, according to the dictionary, the thesaurus, and common use.

          When your projects catch fire because the components from China aren’t what they claim to be, do you just say “Oh, those aren’t fake. They are just synthetic.” Hilarity ensues. I have a “synthetic” bridge to sell you…

          Information that is “massaged” to the point of providing meaningless or false information is meaningless and false.
          When there is no oil pressure sensor, but there is a gauge, the information is false.
          When there is a gauge, but the sensor is just a switch that puts it in the middle, the information is meaningless.
          When the gauge is so non-linear that the needle doesn’t move from center for over 110% of it’s normal operating range, the information is false. (In certain cars, we call them “new engine indicators” because if the needle moves, it’s too late, the engine is cooked.)
          When there is a gauge, but there are no numbers on the gauge the information is meaningless.

          Shall I go on?

    4. If you already have a complete set of gauges any additional OBD data might just be distracting eye candy, but if you don’t have a decent set then OBD can give you very useful fuel consumption, various temperatures, voltage, pressures and others. And it can tell you on the fly what sensor tripped the MIL and whether you can ignore it. Gauges have saved two engines for me (and let me watch a third destroy itself while I couldn’t do anything about it :-( ) OBD makes a lousy tachometer though: response is too slow.

      1. The tachometer in most cars since at least 2000 is connected only to the OBD-II/CAN bus. There is no mechanical or electrical connection directly to the engine or ignition. The OBD-II/CAN bus is more than fast enough for real-time tachometer, the problem is in your display device/software. There are multiple update speeds available. Some external OBD/CAN devices can use the higher speeds for real-time displays.

        1. Maybe the native instrumentation can use CAN, but just plugging into the OBD-II connector and requesting a useful number of PIDs (a dozen or so) yields an update rate of about one set per second, at least with my ELM-like USB interface on the three Subarus I’ve tried it on (2003, 2008, 2015). You can get clever and interleave them if you want to make one or two faster though. I have not tried sniffing the CAN lines.

          1. That may be a function of the cars or the particular ELM dongle. The ELM-327 bluetooth dongle has access to the CAN data and fast update speeds when using Torque.

  2. ODBII bluetooth devide and a smart phone or an android based car entertainment/gps system. My $60 stereo/gps has an ODBII app built in. It has a lot of features built in. Oddly enough it is missing simple car stereo features like a fader for front to back.

  3. This is another example of someone that doesn’t know better blindly connecting to the “Power Supply from Hell”, a vehicle’s “12V” battery bus, not knowing that vehicle OEMs design electrical devices assuming that the voltage on that bus will vary from less then 5V to well over 100V DC!!! There are LOTS of reasons that the nominally 12V to 13.8V voltage on the OBD-II connector does not stay within that range, including almost-dead batteries, starter load dump events, intermittent battery bus/ground connections, tow-truck drivers jump starting with “24V” during the winter, bad alternators, etc, etc. Anyone that designs devices like this “for real” always protects against over-voltage with components that can withstand well over 100V DC. Failure to do this is just asking for expensive failures, smoke and sometimes small electrical fires. Ask me how I know! :-)

      1. Exactly my thought. 100VDC would first of all blow every incandescent light bulb (and probably every single LED one as well) in your vehicle. Along with any display screens as they’re typically rated to 24VDC or so, sometimes 8-20VDC range or whatever. If you ever see 100V in your car’s system all sorts of stuff is going to fry.

        1. Well, it depends how long the 100v is present for. If it’s a short enough spike, incandescent globes will be fine but sensitive semiconductors will die.

          In older vehicles, it was common to see a big souke when the starter motor solenoid disengaged.

          Anecdote time. I used to work for a company that made electronics for mining haul trucks. They kept blowing the power supplies on our hardware, which we thought were rated for higher voltage than anythind you’d ever find in a vehicle. Turns out some of the mine sites were jumpstarting their trucks with a welder!

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