SyncCarb

Description

Trying to build a relative cheap digital instrument able to measure vacuum allowing to synchronize up to 4 throttle bodies (carburators).

At the heart there's a TTGO T-DISPLAY microcontroller flashed with the attached program.
A custom made PCB, an ADS1115 analog to digital converter (4 channels) and 4 vacuum sensors with a range of -100 - 0 kPa powered at 3.3V are all the components needed.

Details

I wanted to build something useful and have the chance to improve my IT/HW/mech abilities.

The results are quite satisfying and could be improved playing with the SW.

Started coding in Python because has immediate feedback (no compilation needed), and once I solved some problems, I rewritten everything in C++ in order to speed up the program and to simplify the implementation for other people.

Important note: the sensors HAVE TO BE -100 kPA to 0 kPA at 3.3V, look in component sections for a link.

Files

Case.stl

3D printed case STL

Standard Tesselated Geometry - 173.52 kB - 04/20/2023 at 11:43

Download

SyncCarb.ino

Arduino C++ version

ino - 4.53 kB - 04/17/2023 at 14:24

Download

Gerber_PCB_Vacuum_2023-01-26.zip

Gerber archive for the PCB

Zip Archive - 59.80 kB - 03/06/2023 at 17:30

Download

video_2023-03-04_12-32-47.mp4

The vacuum meter at work

MPEG-4 Video - 3.88 MB - 03/04/2023 at 12:13

Download

Components

1 × TTGO T-DISPLAY microcontroller esp32 based with display (https://it.aliexpress.com/item/33050639690.html)

1 × ADS1115 4 single channels / 2 differential channles AD converter (https://de.aliexpress.com/item/1005001703504835.html)

4 × XGZP6847A100KPGN33 Vacuum sensors, 3,3V, -100kPa - 0kPa (https://it.aliexpress.com/item/1005003775086286.html)

1 × Custom PCB

4 × Silicon tubes ~ 50cm Outer diameter 6mm, inner 3mm

Project Logs

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C++ vs Python
Mikiquo • 04/05/2023 at 15:40 • 0 comments

Rewritten the SW with Arduino C++
Stable readings
Mikiquo • 03/04/2023 at 12:11 • 2 comments

I almost solved the problem with "jumpy" values.
A SW low pass filter is applied on the min readings of 100 samples (which should catch 2 full cycles i.e. 2 intakes).

Now the values shown are a lot more stable and the throttle bodies can be synchronized by slowly turning the dedicated screws.
Looking at the sensors
Mikiquo • 02/27/2023 at 19:34 • 0 comments

The last picture represents the "analog" output of one sensor attached to a throttle body.
I say "analog" because it's fairly clear the discrete output
First test
Mikiquo • 02/26/2023 at 17:36 • 1 comment

I finally managed to "open" my motorbike and test the device.

I could only connect 2 out of 3 throttle bodies, because the 3rd is in a bad position.

The main problem is that the values read are unstable, they change continuosly.

I thought that reading a value in a random moment, could measure anywhere during the four-stroke cycle.

In order to try to solve this, I read 250 vacuum values per sensor (which takes around 300ms each) and take the lowest vacuum value in order to catch the intake cycle.

It's better this way, but still to jumpy to make a precise measure.

At the moment I don't have any better idea in order to stabilize the readings.

View all 4 project logs

Build Instructions

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Mounting the components on the PCB

Be aware that the TTGO and the ADC are mounted on sockets, therefore the 3D printed case is high enough to accomodate them.

In the first picture, the sensors are also mounted on sockets, but not on the final design because they would be too tall (and could also jump out from the sockets)

Hardware customisation

In order to compile and flash the software, a couple of things have to be done:

In Arduino IDE

add the following URL to the supported hardware: https://dl.espressif.com/dl/package_esp32_index.json
install the following libraries: TFT_eSPI ADS1115-Driver
in the library file ./libraries/TFT_eSPI/User_Setup_Select.h uncomment this only line #include <User_Setups/Setup25_TTGO_T_Display.h>
in the library file ./libraries/TFT_eSPI/User_Setup.h uncomment this only line #define ST7789_DRIVER
choose the right hardware microcontroller (I used TTGO LoRa32-OLED V1 but I think a generic ESP32 would work)

Compile and flash!, you're done!

Take measures

Before turning the engine on, you have to connect the tubes to the throttle bodies and power the device.

This way the device can calibrate to the atmosferic pression.

There's some delay on the value displayed because of the low pass filter applied on the measures.

Discussions

josh.hulbert wrote 02/26/2023 at 20:34

This is neat, but I can see where you'd have issues. All of the carb sync tools I've used have a sort of heavy damping factor built in; early on I used one with mercury tubes, later colored oil. I've never used the newer Motion Pro one with dial gauges but they probably flutter a bit unless they're damped internally. Run a strong low-pass filter on the results and try again. I believe this can be done though!

Are you sure? yes | no

Mikiquo wrote 02/27/2023 at 14:27

Many thanks for your suggestion. I'll try to implement a filter either in SW or pneumatic.

Are you sure? yes | no

SyncCarb

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Description

Details

Files

Case.stl

SyncCarb.ino

Gerber_PCB_Vacuum_2023-01-26.zip

video_2023-03-04_12-32-47.mp4

Components

Project Logs Collapse

C++ vs Python

Stable readings

Looking at the sensors

First test

Build Instructions Collapse

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