DIY Gauge experiments

[TSD]

In case I ever get to finishing the Ibex build, I've been thinking how to get all the instrumentation I want without loads of extra instruments. To keep things fairly simple I want to stay with only the common 3 extra gauges on the dash, but I always seem to have 4 or more things I want to measure. So as an experiment, I've tried making my own, just to see how it works out.

The starting point was finding in rapid succession, some interesting sensors, and a source of reasonably priced round displays. With the current state of global electronics business (and my wallet) the design is driven more by what parts I have on hand, or can easily buy, than what I might have chosen for a 'clean sheet' design. There is a common 'core' circuit board design, with various optional components depending on the intended function.

The one I'm playing with at the moment is combined EGT and boost pressure gauge. This uses a standard EGT thermocouple, and a boost pressure sensor from a Freelander 2, as it's cheapish, and it's nice to use LR parts where possible. The display module is bonded to the front glass (no annoying misted over gauges!) and looks a fairly uniform black face when powered off. I messed up the resin when assembling this one, so there's a visible smear on the lower left quarter which I didn't spot until it had cured overnight . Also, every electronic item must have a boot screen it seems, by some unwritten law.

 

 

The first one I got working, though not yet built up into a gauge, is a combined oil pressure / oil temperature gauge. This is the one that sparked my interest originally, when I found a BMW smart sensor that provides very accurate values for pressure and temperature, from a single unit about the same size as the 300tdi oil pressure switch. This avoids all the plumbing adapters normally needed to fit both sensors, which usually make me nervous. The sensor replaces the oil pressure switch, and the gauge has an alarm output which provides the oil pressure switch function. The oil filter housing has to be redrilled and tapped, but as that's a bolt on housing, it's easy to do and nicer than using adapters.

I've tried a few different graphics designs for the gauges, but the one above seems to be the most legible.

 

The third gauge is intended to be a battery voltage/current monitor, and provide an output to operate a split charge relay. While it could (should?) be the simplest of the three, I've been waiting for parts, and have managed to bundle in a load of extra complexity, so while I've built the hardware, I haven't made a start on the software for this one yet. There are also options on the board for reading from most automotive analogue sensors, and canbus messages, though I haven't tested them and don't intend to as I don't have a use for them at present.

 

The display seems easily readable in bright sunlight, and can be dim enough to not be annoying at night. Certainly less annoying than the nasty chinese radio/satnav. The viewing angle seems more than good enough too.

The housing is 3d printed at the moment (and coloured according to whatever happened to be in the printer!), but is intended to be cnc'd aluminium in the final units. Probably something like Frigefreezers battery gauge housing

 

[elbekko]

Fancy

I wonder if a rotatable ring (like on a watch face) would be a nice way to switch between which gauges are displayed in case you have more sensors hooked up to a gauge.

[TSD]

Aargh! Now I'm stuck - I tried to make it as simple as possible, no moving parts, so it could survive a few years in a wet landy. On the other hand, I really like that idea, and straight away I start schemeing ways it could be done

As it stands now, it does have the option for a couple of external button inputs, but I haven't made any use of them so far.

There is also a single 'tap the screen here' input option, but I've not even populated the circuit board for that.

[David Sparkes]

I like the oil temperature and pressure on one gauge, I think that is usable across a wide range of cars.

EGT & Boost has a more restricted market place.

Regards.

[Anderzander]

Wow - super impressive. I wouldn’t know where to start. Well done 👏🏻 

[elbekko]

3 hours ago, TSD said:

Aargh! Now I'm stuck - I tried to make it as simple as possible, no moving parts, so it could survive a few years in a wet landy. On the other hand, I really like that idea, and straight away I start schemeing ways it could be done

As it stands now, it does have the option for a couple of external button inputs, but I haven't made any use of them so far.

There is also a single 'tap the screen here' input option, but I've not even populated the circuit board for that.

Sorry

[simonr]

I like the gauge!

The idea of a rotatable ring bezel sounds good, but at first thought, it could compromise waterproofing.  On second thought, I figured you could make a snap-on ring with a magnet built in and add a Hall Effect device to the inside of the casing.  That could even be used as an analog input - move the ring fast to change mode, slowly to change brightness for example.

I had a go at making a similar gauge using a mixture of sensors & reading OBD data https://www.youtube.com/watch?v=vjrugu0hZ-0
Waterproofing buttons was an issue so I tried using the little Piezo sensors (like the speakers you used to get in the back of digital watches) as a 'tap' sensor.  They don't need to be mounted directly behind the glass, back of the display seemed to work.  When you tap the display, you get a little voltage spike which is fairly easy to differentiate from general noise / touching.  You can also use it as a buzzer.

I tried a capacitive touch sensor - but they were too prone to accidental touches.

[TSD]

I like the piezo idea. Since they are inherently narrowband, I imagine it does most of the job of filtering rattly tdi dashboard noise before you even read the signal from it

My 'tap the screen' sensor is just an ambient light plus IR sensor behind the glass - the same kind of thing that turns off a smartphone touchscreen when you hold it up to your face. It's simple to detect transient changes in IR level with a finger on the glass, and also measure visible light level to dim the gauge at night. Equally, the same sensor could detect a pattern on the back of a rotating ring control through the glass.

If I was developing this as a commercial product, I'd put an NFC interface onboard to give configuration and datalogging via a smartphone.

I'm as vulnerable to feature creep as anyone, but at its core I think the task is to provide the user with the required information, as clearly and legibly as possible. Ideally, I should be able to glance across at the instrument cluster and straight away know if all the pointers are in roughly the right place, without thinking about it.

Freely admit I've broken this principle with multiple gauges per housing, and unnecessary digital readouts, and it will probably (certainly) get worse with the battery monitor gauge. I haven't even begun to think about how to handle all that. I will get the hardware up and running first and see where that takes me...

 

[simonr]

What I was trying to achieve with mine, was a single gauge which could replace everything apart from the speedo.  Set high or low limits and display those values preferentially if out of bounds - that's the only time you are really interested in them!  The point was to de-clutter the dash.

 

[TSD]

Agreed, in some ways I liked the Citroen approach in the 80s of replacing gauges with warning lights, and adding a 'master' warning light. (The first I was really aware of, though maybe they weren't the first).

But I do like the 'trend' data learned from viewing gauges for weeks on end. It's useful to know if the temperature has suddenly shot up, or been climbing slowly all day, or if it's been marginal on hot days for months. Or, in the case of a tdi, there's no warning light at all because the gauge dropped when all the coolant fell out

With most of our vehicles of course, it's 50/50 if the instrument is more or less reliable than the thing being monitored...

[landroversforever]

Nice project TSD! Cool to see how subtle it could end up. It’s like you’ve squashed a Lascar panel pilot screen into a 52mm gauge!

[TSD]

That's quite funny - I've never seen a panel pilot before, but Lascar head office is in the next village

[Ed Poore]

You've got far further ahead than I have. I sourced a couple of round gauges, wrote some demo code and that's about it 

[TSD]

Like many (ok, almost all) of my homer projects, this one got designed back to front. When I found the smart oil pressure sensors, I wanted to play with one, and see if it was any good. The round displays have been sat in a drawer since before xmas waiting for me to even open the box.

I really hate messing around with dev boards and loads of bodged wiring (at least for digits - it's the only proper way to do RF work!) and I already had a couple of PCB designs waiting to go out for manufacture...

So by the time the ebay fairy brought the sensors, I already had a PCB design. But it annoyed me, because there was space left on it, so feature creep set in, and I started adding things until it began to look busy. All sketched on the back of an old envelope, only a few sums done, and very little detailed reading  of a datasheet.

I didn't write a single line of code until after I'd sent the PCB out.

Not doing too badly for a prototype, only two cut/straps on the board so far, and only one glaring unfixable ****up with the pin assignments. Easily fixable in version 2, which will never happen.

I have the battery monitor version up and running now, but no graphics written yet. Hopefully will have something to show in a few days.

I've been clumsy, one of the displays has cracked so only half of it works. Hopefully the replacements arrive before I get bored and wander off to play with something else, leaving yet another unfinished project

 

 

 

[elbekko]

11 hours ago, TSD said:

leaving yet another unfinished project

Are there any others?

[Nonimouse]

TSD,

Would you be up for amking a second oil temp/pressure guage, for cash money?

[zardos]

On 5/7/2022 at 12:27 PM, TSD said:

I'd put an NFC interface onboard to give configuration and datalogging via a smartphone

I do a fair amount with NFC on smartphones and you might be able to do configuration but datalogging would be hopeless, much better to use bluetooth for both.

[TSD]

2 hours ago, Nonimouse said:

TSD,

Would you be up for amking a second oil temp/pressure guage, for cash money?

If I can scrounge up enough parts to build extras, then I will, no problem. But sourcing electronic components at the moment is madness, so no promises!

13 minutes ago, zardos said:

I do a fair amount with NFC on smartphones and you might be able to do configuration but datalogging would be hopeless, much better to use bluetooth for both.

You are right, I was only really thinking of configuration, where NFC works nicely (or did in the one project where I used it). Datalogging only in the sense of 'Max temp seen since last reset' kind of thing. Maybe some long term stats? I don't see much use for anything more than that, on a standalone box measuring only 1 or 2 things.

Bluetooth would (for me at least) be overkill and not a good fit for the task (of configuration), though it tends to give the marketing department a moist moment. If it was designed as a datalogger, with loads of simultaneous input channels, then live values datalogging would be useful. Come to think of it, I did a design like that years ago, and it was even less interesting than the giant prototype sewage pump it was attached to Thankfully, that had a 3G modem instead of Bluetooth, so no-one had to go anywhere near it

But anyway, this isn't a commercial product, it's just a bit of fun.

[Nonimouse]

15 hours ago, TSD said:

If I can scrounge up enough parts to build extras, then I will, no problem. But sourcing electronic components at the moment is madness, so no promises!

 

Cool beans - let me know what you are trying to scrounge

[TSD]

According to todays junk emails, it's World Metrology Day (how could I have forgotten?), so seems like a good time to post info on the third gauge version I've been fiddling with this week.

This is a battery monitoring gauge, using one of the smart sensors fitted to a lot of modern cars to prevent embarassing failures caused by the Stop-Start systems. There's not really anything new here, others have reverse engineered the sensors before, and Hella will even sell you a box for your motorhome for about £150.  But they don't seem to be widely known about, and I was curious to know what they can really do, and how well they perform. The intelligence of the system is all contained in a single housing, that replaces the ground lead terminal at the battery, and the additional wiring is very simple.  It can directly measure battery voltage, current, and temperature. Current measurement range +/-250A continuously, and quoted as safe out to 1200A, so it should survive even heavy winching (though it might not be an ideal device in that situation because of the voltage drop - more testing to follow). In addition, the unit is a 'coulomb counter', it keeps a running total of energy into and out of the battery. From that information it predicts state of charge of the battery, and comparing measured performance against predicted, the State of Health of the battery.

Because the real 'intelligence' is all contained in the sensor, all the gauge has to do is (other than initial configuration) poll the sensor for the info, and draw pretty pictures on the screen

So here is what I have so far :-

Couple of things to note - the 'analogue gauge' bits of the display are faked, just to reserve space of the screen, and both sets of digital readouts have the same info on them - that's because I only have one sensor connected at the moment. The main readouts are current and voltage, of course. The small value at the left is the 'State of Health' and on the right is the 'State of Charge'. I didn't bother to display battery temperature, as it's probably not very useful, and there's not much spare screen space!

First tests have been very encouraging, the voltage and current readouts are surprisingly accurate, the current reading was well within the 0.5% spec for my Fluke 189, which is the best ammeter I had to hand. Over limited bench testing this week, it seems to track battery stored capacity well, though I'm limited to about 30A for both charge and discharge on the bench. How well it tracks in the real world is another thing of course, but since they are fitted to loads of modern cars I'd hope it could be reasonably useful.

My design as it stands can support at least four sensors (so four batteries) but displaying the info would be fiddly. My use is for two batteries, so that is what I have aimed at.

Now I've proved it can work, I will buy a second sensor and try to get it installed in 1Bex over the next few weeks.

A few pics of the guts for those interested...

 

 

 

Edited May 20, 2022 by TSD
Added link

[elbekko]

Oh, that one is very interesting!