WIP: Heads up display for P80

yanga001 · Post by **yanga001** » 18 May 2021, 07:51

Hi Everyone,

I am making this post as a log for a little project in the works. The problem i have is that i am too lazy to look down at my speedo during normal driving and like to darken the surroundings when driving at night. After doing a bit of digging i found that the 98 V70 instrument cluster has a 12 pulse per revolution accessory output on the top that is ripe for tapping.

I did some preliminary sourcing on digikey and found some cheaper TFT and OLED displays that could be used to reflect onto the windshield. These displays are optimal over LCD as they can handle the harsher Canadian temperatures that we get to enjoy.

Bonus connections would be to tap the fuel sensor and try to calibrate to have a digital measurement of how much fuel is left. A tachometer would be cool as well but would require splicing into the sensor network.

Milestones:
i) 1st stage of board design and development. It seems the silicon shortage has somewhat cleared up in terms of 3.3V IC's and i have some leftover micro controllers to embed and design with.
ii) calibration with a pure speed measurement. (starting small with this and just want to get the speed displayed on the screen. Will see how well the screen reflects, although preliminary tests with a smartphone screen seem to indicate it will work well).
iii) expand and tap more controls for display.

The goal of the project is to add a bit of that modern luxury to an old dog. If it works well then maybe lane sensing is a next test, got to put that EE degree to use.

Post by **volvolugnut** » 18 May 2021, 08:14

I admire your can do approach. Perhaps there is a market for such upgrades.

volvolugnut

yanga001 · Post by **yanga001** » 26 May 2021, 15:37

Did some research on it. My plan is to use a few LED dot matrices to do the illumination. I trust the brightness a bit better and they are far cheaper. I was looking at LTP-757G on digikey as they seem to be fairly cheap and well in stock. The C connector on the speedometer gives pulse per revolution so ill need to take an average over 1-2 seconds to determine the actual speed. I assume this is RPM at the wheels and not of the engine.

The reasoning between this choice boils down to cost. A small OLED or TFT display seems to cost roughly 15-30 for a 1 inch diagonal.

The smaller individual modules are about $4 a pop with dimensions of 0.7 inch diameter. Might order a few and see how they look at night and during the day when lit up.

https://www.digikey.ca/en/products/deta ... Cg5iAugXyA

Second issue i came across was driving these bad bois. LED's take off the cost by adding onto complexitiy. These follow a schema called charlieplexing where we can apply a voltage across two different pins to light up a specific dot on the matrix. For my purposes, it is more then likely that i would need to source a small LED controller chip which would add cost.

https://www.digikey.ca/en/products/deta ... 2RI/252588

I am thinking of doing the digital speed on 3 7 segment displays as it can be controlled directly with a chip such as this.

https://www.digikey.ca/en/products/deta ... P/13420598

which provides 24 outputs. At most the speed could be 888 which is 7*3 which is 21 segments. This is good as i can separate the power and control for speed in this way.

This post is a bit scattered, but the direction i am taking is to order the cheaper, larger 7 segment displays for the purposes of displaying the speed. This should achieve my minimal goals for the project. In terms of prototyping i need to breadboard these displays and test their brightness in day and night use. Once done, then and only then will i consider getting the controller chip and programming it separately. I realize that the OLED displays are more integrated and less hardware heavy however they cost more and are smaller.

Before any of the above i will try to log the data line from the accessory output and see if it scales well. I am thinking that its 5V logic but will double check when i get some time.

Post by **BEJinFbk** » 26 May 2021, 19:21

Have you thought about throwing an
Arduino or maybe a Raspberry Pi at it?

You can also find a speed signal at the
back of the radio, if that helps. It gives
the HU speed for Auto Volume Control.
Black/Yellow, IIRC.

yanga001 · Post by **yanga001** » 26 May 2021, 20:58

@BEJinFbK My plan was just to use a scope with an inverter to power it to start. I am unsure of the logic level so i do not want to fry any chip. I didnt know that and will try tapping it too.

Post by **RickHaleParker** » 26 May 2021, 21:43

You might want to take a look at VTL's Driver Distraction Display for inspiration. You can get a lot of information from the CAN Bus.

Arduino Volvo Display Thread.

850oldschool · Post by **850oldschool** » 27 May 2021, 10:54

Does the car have CAN, or is it ISO 9141 like the 850's?

yanga001 · Post by **yanga001** » 27 May 2021, 15:11

I am pretty sure these are ISO9141's. No mention to a CAN bus in the 98 schematic. Looking at the 2000 schematic it adds can communications across a few pins.

Post by **RickHaleParker** » 27 May 2021, 17:29

esl_97_850_T5 and xanthefin are the two you should hope to tap for this project.

xanthefin is the author of 850 ODB-II and esl_97_850_T5 is the author of volvo850diag which 850 OBD-II is based on.

yanga001 · Post by **yanga001** » 27 May 2021, 18:19

Turn off volume, was running an inverter that was not happy with how low the car voltage dropped while running. It’s nothing to be worried about. I am going to try and avoid tapping the obd2 as it would require far more processor then I would like and cost more. I am looking at a sam07s and i now realize that I will need a logic level converter as it’s 12v logic.

IMG_1011.MOV: Video; (27.79 MiB) Downloaded 148 times

Thanks RickHaleParker & BEJinFbK as a later iteration may include OBD2 with a FT232RL and a esp32 wroom. That would allow for hosting a webgui off of the esp32.

With 12V logic i would need to step down to 5v or more likely 3.3v as required by the device.
https://www.digikey.ca/en/products/deta ... Q1/2353345
since it is a square wave it should translate nicely with negligible delay.

Did some math and attached the sheet of it. Looks like i am not looking at anything crazy in terms of polling rates to capture our period. I might see if a simple counter chip can be implemented, checked, and reset every second to determine the speed. I am thinking a 1second delay in speed should not be an issue (will likely be less than that) (roughly 400Hz max from my calculation, assumed 400 pulses per second which on 205's is roughly 225 km/h). I do not aim to get anywhere near that, but might go higher to fit the spec of a turbo

.

Since the frequency is so low i am tempted to utilize a counter as 10km/h should equate to roughly 15-16 pulses per second.

https://www.digikey.ca/en/products/deta ... PWR/377024
datasheet for the counter
https://www.ti.com/lit/ds/scls160d/scls160d.pdf

I found that this 12 bit asynchronous set and reset counter could be very viable as a means of counting the number of pulses given a fixed amount of time. I am thinking of sampling ever 0.5-1 second and then checking the counters output value. Then reset the counter and repeat the cycle. The processor i am going to use will likely support dual core operations so one core can be dedicated to the counting/sampling while the other core can be used for output. This is where a real time operating system comes into play as it can allow for threaded or parallel processing.

I will do some more math to see what my accuracy would be, however i am leaning towards a logic level unidirectional TTL to input the 12 bit counter as a means of measuring the number of pulses and then reseting in fixed intervals. I will need to include a switch to go between rim and wheel sizes for greater accuracy.
MATH HERE

DOC034.PDF: (281.35 KiB) Downloaded 193 times

I will set up a block diagram soon for all this.

EDIT:
After going through the datasheet for some atmel chips i realize that they integrate the counter. Therefore i might be able to get away with just a logic level conversion fed straight into the atmel chip.

https://ww1.microchip.com/downloads/en/ ... 02061B.pdf