Firstly I’d like to say im 95% new to a lot of this, but decided I want to dip my toe in and see how I like it although I’ve always wanted to start making things like this.
Basically my plan is to set up some gauges for my car. Originally I just wanted to have boost but it would be great to have a few and be able to cycle though them with the buttons. Theres two ways I can go about it as far as I can see and basically the first one is to just have inputs from the single items I want but that’s kinda bulky or I wonder if there is a way to read off an aftermarket ECU from the CAN line?
So i bought a Gameboy advance SP shell and the simple plan is to get a screen to fit into the GB screen placement (3" or bit smaller with the provided surround) and run the brain either in the GB shell or I can just put it all in a box somewhere and just wire up to the screen/buttons if theres no way its fitting.
So quick run down on what I want to achieve:
-Find screen to fit into GBA:SP (I asked someone at core and they said maybe this one)
-Decide if Arduino or R Pi is a better option
-Figure out how to communicate between ECU or single inputs.
-If possible to use buttons on GB in some way.
Ive checked out a few videos on YT and there’s a few kinda similar here and here. Ideally I would love to have some graphics and not just an input number. Would love it to look somewhat similar to this but that picture shows a working GB with an accessory attached (So its a dedicated boost controller/tuner)
Let me know if this is something defiantly do-able and any pointing in a direction would be appreciated!
I’ll post my progress (theres no hurry so it’s gonna be slooowww)
Yes I think you can do this!
See if you can turn your steps above into questions like
E.g. Can I get that LCD screen to print “Hi Alex”
E.g. What kind of values come out of the boost sensor.
Of the two videos you linked, the Arduino route seemed simpler.
The LCD screen you linked should be able to handle the graphics, which are mostly static except for the dial. It’s all looking like it will come together.
Do you already own a boost sensor?
Did you say you have an aftermarket ECU? What brand? Maybe they have some documentation regarding their interface protocol.
A few years ago I thought it would be cool to get a boost gauge for my Subaru, and after asking in a forum and going down a rabbit hole or two, ended up just installing a (Subie-specific) thing called BTSSM on a spare phone, and plugging it into an OBD adapter. All the gauges I could ever want, and it turns out I wanted an accurate speedo (which includes a correction factor for different sized tyres from stock), way more than a boost gauge. Probably the niftiest thing about it is the logging function, which is an infinitely cheaper alternative to dyno time for tuning purposes.
Not sure if there’s an equivalent to BTSSM for Haltech ECUs or whatever
Oh yeah, interesting thing I learnt with this - even though BTSSM is presumably getting the same signal from the CAN bus as the stock speedo, it read around 5kmh slower (the error seemed a bit non-linear, but did scale slightly with speed).
The factory speedo is intentionally borked to make you drive slower. It’s not just Subaru either; I’ve checked the speedos of multiple cars against GPS, and it’s rife. So if you’re like me, and consider the true speed limit to be the fastest you can go without being booked, that’s roughly around 8-9kmh faster than indicated (of course, check that against what your phone tells you before relying on it).
Hi Kimmo
True, the car speedo is usually in error. I once took a car back to the dealer and claimed the speedo was about 7km fast at 100kmhr. This I established using the accurate 5km provided on the Hume motorway and a stopwatch.
The dealer produced the specified requirement (in NSW anyway) which the speedo shall read -0 to +10%, so mine complied with requirements
The GPS is not the holy grail either. The accuracy has a bit to do with the number of satellites in view at any one time. Also I think the system measures the distance travelled in probably the update time (1 Sec with mine) and calculates speed. Considering the slight error positioning there is a possible error here. Also I think (I could be wrong here) the system is measuring horizontal speed, not accounting for slopes. If you are going up or down a very steep hill this error could be considerable. Take an extreme instance where the slope is 45º (I know, this is extreme but a convenient example). You will actually be travelling 1.414 times the indicated speed or indicating 0.707 of your actual speed.
I agree the GPS is very convenient and is good enough for practical purposes and I would have nightmares trying to produce a car speedo that is anywhere near accurate at all speeds. Depends on too many factors. One being the effective radius of the wheel and tyre will get larger at speed when centrifugal forces take over. This in turn depends on tyre pressure at the start, tyre make and type and probably wear, even the ambient temperature probably. So all things considered while the spec seems to be very wide it is probably not too outlandish when all factors (like what happens to the car when it has been in circulation for a while) are considered.
I have a chart somewhere showing different tyres and effective wheel sizes at different speeds. I will try to dig it up and find out where I got it when I get a chance.
A bit of interesting trivia: I think those vehicles (Won’t call them cars) designed for land speed attempts have tyres that intentionally expand considerably at the very high speeds. Like a variable overdrive in your gear box.
Cheers Bob
For sure the GPS won’t be 100% accurate, but it’s probably the most accurate way to find a speedo’s error, probably to within 1kmh I’d guess.
I have to admit, whether the road is ascending or descending hadn’t occurred to me, but a typical gradient which seems more or less flat is only going to introduce the most minimal of errors… Not sure how much the number of handy satellites affects things, but the number of GPS networks a phone can access is one of the things I look at when I’m researching a new one; pretty sure my Samsung A71 is 3/3 on that score. It’s fairly easy to double check anyway; every time Google Maps is giving you directions, it shows your speed.
As for the centrifugal expansion of tyres, that’s another angle I hadn’t considered, but it occurs to me that modern cars festooned with cameras pointing in every direction could easily be made to calibrate their own speedos with a little bit of code; they’d just need to know the distance between a couple of points on the road that a camera on the front and a camera on the back can see, and be able to periodically pick a feature to watch pass by, at a range of speeds.
That’s if anyone gave that much of a stuff about it - seems like a majority of drivers these days are happy to do ten clicks under, or even twenty under in 80 zones, for some reason
…Oh hey! The centrifugal expansion explains the non-linearity of the speedo error as exposed by GPS! If it says you’re doing 55 when you’re doing 50, and you expect it to say you’re doing 110 when you’re doing 100, but it only says 107 when you’re doing 100, there you go. Perhaps the speedo in BTSSM has a fudge factor for this, because once I have it calibrated with a correction factor, it’s always within 1-2kmh of the GPS reading.
Welcome to the forum!! Sounds like a siiiick project!
Would it be possible to send through measurements for the insides of the GBA? We can check through and see if any screens are compatible.
Both are very good options, but you should consider how complex you want the graphics to look as that will decide what processor you go for, reading CAN or a simple sensor is trivial.
I dont have experience with CAN on a car so milage may vary.
If you can grab the ID’s of the sensors you want to read and the way the data is packed then you’ll be able to convert this to something you can output, Kimmo had a good experience with an OBD adapter from the ECU, you’ll also need a CAN transciver and a peripheral that can relay CAN to something else (on microcontrollers like a Teensy 4.0, which would be the micro that I go for).
Yeah for sure! You’ll probably have to do some hacking to install/access them but definitely do-able
Liam
