JT's Custom Instrument Cluster Thread

[JehTehsus]

Progress continues!

Been a fair bit of work going into the firmware on the first batch of proto-boards lately, unfortunately nothing really to show as it is all groundwork type stuff and no fancy mechanical action or anything at this point. I probably won't actually show off the code running until I get the second 'form fit function' prototype boards built up and operating; at that point things are much closer to the final product (hopefully) and there will be lots of goodness to show off.

In other news, mechanical design has been moving along a lot in the last few days. I actually have a large format 3d printer I am going to be setting up very soon here (the kit is behind where I am sitting right now) that will be used to fabricate the majority of the enclosure. I expect printer setup and calibration to take around a week, after which I will start printing draft models.

Speaking of draft models... here we go:



There are obviously still some aspects missing - primarily dials and the front cover window (as well as the car chassis mounting points), but the general shape of things can certainly be seen. As well, the cosmetic tidbits (like smoothing/chamfering various edges and whatnot) are not in the model at this point, these are things best left until the very end.

I am going to be doing all the initial mechanical prototyping with the 'classic' layout. There are a number of things that will need to be fine-tuned by doing a few test prints, which include things like hole sizes and mechanical clearance between the printed assemblies. The enclosure is mostly going to be flame retardant ABS; but the light pipes and (if I can get it to work) window cover may well be something like polycarbonate. ABS isn't always the best for dimensional stability, especially larger prints, so tuning will definitely be necessary.

The enclosure itself has been broken down into a few separate parts that will all be printed individually. Taking some time to optimize this for the FDM process yields significant dividends in saved plastic (cheap) and printing time (never enough). You can see these parts in the following snapshots:



This inside view showcases the lightpipes (in green), the brackets/skirts between pipes to both hold them in place and to prevent excessive light leakage between LEDs (in dark grey) and the dial control knob (red).



The rear of the enclosure is two pieces - the large yellow main backing piece here which essentially just covers the circuit board and has connector cutouts, and a brownish piece that acts as a cover for the relatively large power supply filtering front end.

Here is a snapshot of the front cover piece in the slicer program, where it will be printed from:




Overall I hope to have the next draft of boards in relatively soon. There is still a fair bit of code to write, and definitely at least a few more days of drafting time in the enclosure (especially once the first few are built to validate clearances and everything), but things are gradually progressing towards a road*-worthy prototype.

*not public road worthy of course; this is not legal for street use (at least in Canada).

[JehTehsus]

Short update this morning, mostly just to show firmware is slowly coming along. As I mentioned previously, I have been focusing mostly on low level/backend (i.e. all the boring stuff that makes a project tick) stuff that really does not seem to do anything, except make the rest of development much, much easier. Anyway, yesterday I decided to tackle some low hanging fruit, and implemented the low level LED driver along with some testing:





Even in the second picture (which is also a different time of day) the LEDs are not at max brightness. Currently the colours don't mean anything, the first picture I was fixing some of the control protocol and had an interesting unintentional purple color, the second picture shows a random ring of RGB colors I generated after everything was working.

It can be difficult to gauge how bright they are from pictures, but for reference it starts to become uncomfortable to look at, say, blue at 50% brightness (and the brightness scale is not linear), never mind easy to see even with the sun in your eyes. I watched the dial beside me on 87% brightness doing the random color cycle, and I have been blinking afterimages from my eyes for the past 60 seconds. When all three colours are active the things really are blinding. My tiny little supply I am using at the moment actually starts to brown out around 80-85% so I can't really bring the brightness above that (this is not the production power supply, just what I am using for the test board). Point is, even with a cover that diffuses a lot of the light, they are going to be more than bright enough IMO for both casual evening cruising and an oil pressure warning on a sunny track day.

The other big item of interest with the LEDs is update speed. My driving motivation for the design (of the LEDs) is that they need to be fast enough to update that, even pumped full of adrenaline on a race track, things seem smooth. There are a few factors that play into this, but the biggest ones are the actual LED update time - i.e. if you think of the LED as a pixel, how long does it take to change from one commanded color/brightness to the next - and the processor control and communication time with the LEDs. These LEDs are quite common - built on the APA102 - and the update rate of the individual LED is 400Hz as per the datasheet. 400Hz is quite fast, I don't think this will be a limiting factor in the production design. This leaves the other half of the equation - i.e. how fast can the processor actually control and communicate with the LEDs? Now, of course, the CPU is going to be doing lots of things - measuring vehicle inputs, filtering and scaling these values, applying user configured transformations and then updating outputs, which consists of LEDs, PWMs, and stepper gauge controls. So the LEDs are only a small part of the equation. It is too early to say how long all of the LED update operations are going to take - I need to write the code that transforms the inputs for each string of LEDs to produce meaningful information, like current gear positions on the tach and oil pressure warnings. That said, another part is how long it takes the hardware to send all the data out to a string - this I have measured. In this case, on the test bench here with the prototype board, fully updating 16 LEDs takes approximately 100 microseconds. If I reduce the clock speed by a factor of ten (something I may do to reduce electrical noise) then the time climbs to ~650 microseconds. So long story short, in terms of hardware limitations, updating a full cluster worth of LEDs (~72) should take no more than 3 milliseconds, and since most of this is handled by a buffered output port, the actual processor time involved is on the order of tens of microseconds, with it going off to do something else while it waits for the message it has queued up to actually make it to the LEDs.

Overall I am fairly happy with things. I do need to add some termination resistors to the design to reduce ringing, especially at the higher clock speeds, and I may add a copper pour around the outer edge of the board to improve heat-sinking for the LEDs (heat is definitely a non issue on the bench, even running them as hard as I can they do not get more than slightly warm to the touch. But the actual operation of them in the car will be warmer - so more heatsinking is good). Once I get the next stage of prototypes built up I can also test the logic that controls LED selection, as well as proper tests across the entire brightness and power range.

[JehTehsus]

Short little update today.

The PCBs have arrived! Almost done finalizing the BOM for a prototype run; hopefully order those tomorrow and have them in on Monday. It is the ladies birthday weekend this weekend, so I can't go near any of my projects anyway.

Also, the 3d printer is coming together. I suspect this will be actually ready to print early next week as well, so once I run through all the calibration I can get started on enclosures.

The PCBs:


The printer:

[JehTehsus]

In terms of progress, things are moving along reasonably well.

I did encounter some issues with the connector pinout... naturally I spent much more time reviewing the mechanical board stackup than verifying all the electrical signals were going to the right places. Basically I flipped the signals on the main connectors, which means I will need to do at least one more version of the large backing board before the setup is vehicle ready. Definitely annoyed about this, but it just means I need to run a bunch of jumper wires for the prototype so not really a huge deal; I can still get everything working on the bench (and mounting the main control board on wires is actually good, because normally I cannot access most of it for testing with the scope).

In other bad news, I also shorted one of the MCUs after getting it all up and running. There are a grand total of 2 places on the board you can easily short the 5V power rail into the 3.3V processor I/O, I ham fistedly probed one of them and did exactly that. "R&D" everybody. Not the end of the world, but annoying since it is the worst part to change out.

In good news, the time spent verifying the mechanical stackup paid off! I have also been playing a bunch with the 3d printer and getting it dialed in for ABS. Still some warping and other minor issues, but it has only been a few days and I feel I am making steady progress in terms of quality, overall I am quite optimistic.

Here is a mechincal mockup of the PCB stackup. It won't actually run like this because I need to flip the connector signals, but it does fit together and mechanically no significant changes need to be made (note: there are no standoffs in place at the moment, so things are a touch loose, but it gives a good idea of how it will all go together):



This also shows off how the 'econometer' will be accomplished for the classic variant. The DTM variant will have the option to install a small display in this position on the large dial as well (I suppose I can do the same with the classic variant as well, if someone wanted a display instead of a gauge there for some reason):



You can see the (literally very first) proto run of the enclosure wrapped around the board here:





This is being printed in ABS, and as I noted there is some slight warping around the edges where they are curving back in, which obviously isn't what I want and will hopefully be eliminated soon.

So overall, things are moving along. Faster than usual now as well since my last contract ended rather prematurely (the one problem with startups I have found is they all too often run into money issues...) and I have a lot more time to pour into this. I am looking forward to making some really significant progress on the project before diving into more actual work.

[bmwman91]

Nice progress there. Yeah, no matter how careful you think you are being, it's almost inevitable that you'll mirror a through hole footprint at some point lol.

ABS is a bit of a pain, I have found. My printer is a lot smaller and has walls enclosing it, and that seems to help a LOT with warping. The heated build platform is not, on its own, quite enough, but being able to trap a bunch of heat in there seems to improve things. Maybe you could try a tarp or something quick & dirty like that to see if keeping the interior of the printer warm would help. Thankfully, I mostly run PLA which actually requires the printer to be "wide open", but anything that goes anywhere near the firewall or under the hood definitely needs to be ABS.

[JehTehsus]

Nice progress there. Yeah, no matter how careful you think you are being, it's almost inevitable that you'll mirror a through hole footprint at some point lol.

ABS is a bit of a pain, I have found. My printer is a lot smaller and has walls enclosing it, and that seems to help a LOT with warping. The heated build platform is not, on its own, quite enough, but being able to trap a bunch of heat in there seems to improve things. Maybe you could try a tarp or something quick & dirty like that to see if keeping the interior of the printer warm would help. Thankfully, I mostly run PLA which actually requires the printer to be "wide open", but anything that goes anywhere near the firewall or under the hood definitely needs to be ABS.

Yeah, ABS has it's challenges for sure. I actually do have an enclosure, and the bed heater is as high as it will go (PEI on aluminium @~110-115C). I think my challenges are more so related to bed leveling - the large bed definitely isn't perfect, and what is less perfect is my application of the PEI sheet. I may have to drop on a piece of bs glass, but for now for prototyping it is not a big issue.

[bmwman91]

Aah, yeah leveling can be a pain. I printed a clip-on bracket that holds a dial indicator and slides on the linear shafts, so I do it that way. If the build plate itself is not very flat, or warps badly when heated due to thermal expansion mismatch between it, whatever it mounts to and the (guessing) FR4 resistive heater board, then printing the raft can help to "absorb" the warp. Sadly, that means printing a raft, and I hate them lol. I don't need one with PLA, but ABS seems to demand it more often than not, and aside from material waste it means that the bottom face usually has crap cosmetics.

Anyway, I do my leveling after pre-heating everything and sitting at operating temperature for ~15 minutes as I have found that the nozzle gap to the build plate changes enough to make problems if I level and gap it when cold.

[JehTehsus]

Aah, yeah leveling can be a pain. I printed a clip-on bracket that holds a dial indicator and slides on the linear shafts, so I do it that way. If the build plate itself is not very flat, or warps badly when heated due to thermal expansion mismatch between it, whatever it mounts to and the (guessing) FR4 resistive heater board, then printing the raft can help to "absorb" the warp. Sadly, that means printing a raft, and I hate them lol. I don't need one with PLA, but ABS seems to demand it more often than not, and aside from material waste it means that the bottom face usually has crap cosmetics.

Anyway, I do my leveling after pre-heating everything and sitting at operating temperature for ~15 minutes as I have found that the nozzle gap to the build plate changes enough to make problems if I level and gap it when cold.

The plate isn't too bad, the modix runs a 100 point (by default, I may bump it up to 400) compensation mesh on a duet 2 which after a few passed I managed to get dialed in quite well and it made a huge difference. It can't compensate very well for a couple of air bubbles I have under the sheet though, and my best attempts at removing them have been less than perfect. Overall I have only been printing with it since last week (first go with a 3d printer too) so there is still some learning on my end, but I feel I am making steady progress. I have only ever tried dialing in the offsets and leveling with everything being heated overnight and I noticed a pretty big difference between the offset adjustment during first setup and once everything had warmed up.

[bmwman91]

Ha damn, 100+ point mesh correction, fancy stuff. I just do a 3 point manual adjustment on my Makerbot clone lol. It's a heck of a lot smaller, so I guess that much makes it easier.

Bubbles under the film sucks. No luck poking through with an x-acto knife to deflate them?

[JehTehsus]

Ha damn, 100+ point mesh correction, fancy stuff. I just do a 3 point manual adjustment on my Makerbot clone lol. It's a heck of a lot smaller, so I guess that much makes it easier.

Bubbles under the film sucks. No luck poking through with an x-acto knife to deflate them?

Definitely helped in a few spots, but I certainly wouldn't call it perfect. Some of them just do not want to deflate completely it seems.

You can see it really well in this - this is the second pass at doing the rear of the enclosure. Overall I am pretty happy with it but it is very obvious where the bubbles are.... Luckily I have plenty of print bed space so I can move this around a few inches and likely avoid them completely. The rest of the gunk on the back is just the impression left by the glue I experimented with when printing the lady some hooks, as well as some bits of the skirt I didn't remove. The big test with this piece was to see if I could avoid warping - and the answer is yes, the part did not peel from the bed at all. The final big item to address is that some of the screw mounts are simply getting overheated on the top surfaces due to their small size, so I may try a very, very low fan speed and see what kind of results it yields,





In other news, bringing up the boards is going fairly well. Only real challenge has been the stepper motor driver chip, which is precisely 4.2mm X 4.2mm with 24 'pins' that are actually just wrap around tabs. If you google "QFN24" you will get a picture, basically try to imagine soldering that when it is smaller than your pinky fingernail. And yes, there is a large pad on the bottom. 3 tries later I finally got it actually working, thankfully the one mounted on the main board will be machine built, as well as the very simple auxiliary boards, because these chips are not really hand solder-able unless you have a decent setup (hot air gun, paste, etc) and some experience. Currently my vision for the kits is having the complex control board machine assembled as well as the very simple aux. gauges, as those are cheap to do in large batches. So the kit itself would require some soldering for the large backplane board which is fairly easy (some 0603 resistors and a few ICs, but nowehere near as bad as the main control board).

Anyway, all that aside I went through 3 chips before I finally soldered one completely correctly. You can see it in action here:

https://youtu.be/Jv5iLYTqgyQ

Note that it is really noisy on the 'slow' movement; this is my lazy ass just hacking together some quick test code. It is actually much quieter during properly controlled movements, the movement at the start of the video where it sweeps all the way back to the home position is a better example. The 'buzz' sound is me firing up the big ol power supply.

This leaves a few other bits to get setup on the main board. Note that this does not mean 'fully programmed' - what I am doing at this stage is writing software that just performs some basic tests and lets me ensure the hardware is built correctly, so there is still some significant effort to go. Essentially the board bring up checklist looks like this at the moment:

Tested:
-Power supplies, including analog reference
-Processor
-UART/serial port for PC communication
-I2C multiplexer
-Digitally controlled LEDs
-On board LED chain selection logic (the pcb can drive LEDs on a separate attached gauge, there are some switches that let it essentially decide what LED string it wants to control)
-Stepper motor driver
-Voltage level shifting logic

Not tested:
-Motor selection multiplexer
-EEPROM
-SD card
-RTC and battery backup circuit (note, no actual battery is on the board - I mean the circuit that lets it run off the vehicle battery. This needs to be extremely low current consumption and verified to be so since you don't want it killing the battery. If you were running just the RTC off a fully charged battery it should be good for many, many moons)
-Analog input filtering

The SD card and EEPROM are extremely low risk, basically cookie cutter stuff I have worked with numerous times. The RTC is a chip I selected but have not used, and while not as bad as the motor driver was also a really fun one to hand solder, so that is next up on the hitlist. This leaves the following bits, which are actually on the backplane board and not the main control board:

-Various LED strings
-Main LED control multiplexers
-Digital character display
-Rotary switch/knob
-High voltage VR input for the diff speed sensor.
-Pulse input sensor for the tach. This is a little tricky because on some E30s it is a nice easy output from the ECU but on others it is much uglier (electrically speaking; physically it is as ugly as any other wiring mess) and comes from the ignition coil.
-All analog inputs, including filters and protection circuits
-All generic digital inputs and filters/protection circuits.
-Power down/power control circuitry.
-Careful verification that all factory signals are going where i expect. This is a pain in the ass and will be left to last.

Somewhat lower priority, but also fairly low risk since I have worked with them before (and therefore will be left until last):
-GPS. Chip shortage seems to be affecting this part too, there are some substitutes I could likely work in though.
-CAN transciever.
-USB adapter (FTDI)
-EEPROM

The small auxiliary gauges are actually just copies of the motor control setup on the main board, with a connector and an EEPROM identifier, so those should be very quick to validate design wise. I do need to fix some signals on the connector, which requires a board spin, but I can easily work around that with wires for my testing.

Anyway, things are moving along, bit by bit.

[bmwman91]

Damn, yeah those are some sizable bubbles! No possibility of peeling the film off and replacing it? I'm surprised they could not be popped, unless there is some crap trapped under them.

Good stuff with the electrical proto work. It's always satisfying to see stuff working for the first time! Also, QFNs in general are the devil for hand soldering, especially fine pitch ones, and doubly so for ones with big thermal pads! A future project is going to be to use a T-type thermocouple, a PID box and a toaster oven to build myself a reflow oven. A guy I work with uses an un-hacked toaster oven for reflow and it seems to work fairly well, so I bet one that can follow a closed-loop profile would be great.

[JehTehsus]

Damn, yeah those are some sizable bubbles! No possibility of peeling the film off and replacing it? I'm surprised they could not be popped, unless there is some crap trapped under them.

Good stuff with the electrical proto work. It's always satisfying to see stuff working for the first time! Also, QFNs in general are the devil for hand soldering, especially fine pitch ones, and doubly so for ones with big thermal pads! A future project is going to be to use a T-type thermocouple, a PID box and a toaster oven to build myself a reflow oven. A guy I work with uses an un-hacked toaster oven for reflow and it seems to work fairly well, so I bet one that can follow a closed-loop profile would be great.

Yeah, a small oven would be ideal. I have used little IR ovens in the past and they work great. I need to make up my mind about whether or not it is worth it to get one - given my likely very low production volumes it may well be cheaper to farm out the build, but it would be really nice for prototyping or even just doing partial kits where the end user has to assemble all the not impossible to hand solder bits.

In regards to the bubbles... yeah they are a pain. But luckily the bed is so massive that even with some bad spots, I can just move a ~350x200mm part around a bunch and avoid them. The second draft of the front just finished, zero warping this time (finally think I have that all dialed in) and the two second draft enclosure pieces fit together great.

I definitely need to slightly widen the factory connector holes, a bit too snug of a fit for my liking right now. I am also working towards a modified rev of the backplane where one LED is in a better position, I was originally thinking of an angled light pipe but I don't think it is going to work nearly as well as just adjusting the LED position.

Overall I am extremely happy with the dimensional accuracy across the part. Everything I read about 3d printed ABS seemed to indicate shrinkage made for smaller parts - mine seems bang on to where I want it, certainly within the tolerances I used when modelling the draft (at least now that it isn't peeling off the bed). The only minor nitpick is hole sizes are definitely a little small, but this is to be expected, especially in the small flat pieces where the extruder hot end spend a lot of time remelting around the holes. And realistically I just need a guide hole of roughly the right size anyway for a screw to get some decent bite into the plastic. Since this is not something that will be coming apart often I don't think it is worthwhile to integrate nuts or anything like that. Just holding the assembled front and back piece with only half the screws installed, the unit feels very solid.

Here are a couple more snapshots, I still haven't removed the glue from the bed and I did zero finishing work, but there aren't any big bubble spots :). And yes... the ABS is switched to transparent partway through. Finally burned through my first kg of plastic!









It really is too bad I buggered up the wiring on the main connector, if it wasn't for that I could actually power the board as shown here. As it is, the dual 60 pin headers are backwards and when plugged in short power and ground (oops), so i can only power the board when the 104mm gauge is disconnected and tied in with jumper wires instead. There are a few other minor things that need to be fixed, like the LED position and some series resistors here and there, so a board re-spin is needed regardless. I also still have to check the factory connectors, which I will be getting to shortly.

[Elysian]

Yeah, ABS has it's challenges for sure. I actually do have an enclosure, and the bed heater is as high as it will go (PEI on aluminium @~110-115C). I think my challenges are more so related to bed leveling - the large bed definitely isn't perfect, and what is less perfect is my application of the PEI sheet. I may have to drop on a piece of bs glass, but for now for prototyping it is not a big issue.

I've recently switched to ASA, and far prefer it to the other materials I've printed in (PLA, PETG, ABS). It doesn't shrink like ABS, is easy to sand/finish, and is strong, real strong. I use it as the bobbins for custom guitar pickups, which wind up under a lot of tension after they're wound with thousands of winds of extremely thin copper wire. Stands up to heat great as well. I was printing on my MK3S's stock PEI steel plate, but recently switched to the Prusa powdercoated satin sheet.

edit: On bubbles, I've had to deal with them a bit, pierce them with a needle and press the air out. The hole isn't large enough to cause any issues, but is large enough you can get the air bubble out.

[JehTehsus]

I've recently switched to ASA, and far prefer it to the other materials I've printed in (PLA, PETG, ABS). It doesn't shrink like ABS, is easy to sand/finish, and is strong, real strong. I use it as the bobbins for custom guitar pickups, which wind up under a lot of tension after they're wound with thousands of winds of extremely thin copper wire. Stands up to heat great as well. I was printing on my MK3S's stock PEI steel plate, but recently switched to the Prusa powdercoated satin sheet.

edit: On bubbles, I've had to deal with them a bit, pierce them with a needle and press the air out. The hole isn't large enough to cause any issues, but is large enough you can get the air bubble out.

Are you aware of any flame retardant ASA's? Overall I would definitely prefer to use it, better UV stability as well as all the other bits you mentioned. However, none of the ASA filaments I can readily find seem to be flame retardant/self extinguishing, which is something I would really prefer to have (especially for track usage).

[Elysian]

Are you aware of any flame retardant ASA's? Overall I would definitely prefer to use it, better UV stability as well as all the other bits you mentioned. However, none of the ASA filaments I can readily find seem to be flame retardant/self extinguishing, which is something I would really prefer to have (especially for track usage).

Never looked into anything like that, but I feel like just about any filament you could use wouldn't do well in a fire situation. Lots of plastics in cars are ABS as it is.