The idea is simple build a tool inspired by Reekon M1 caliber tools https://www.reekon.tools/
I need a tool to measure the lengths that I cut on my saw. Simple no ?
Constraints :
- Precision : 0.5mm < x < 1mm
- I must be able to measure different subjects (steel, wood, plastic...)
- As small as possible
- Build all I can
- Cheaper
Just a little math for the precision calculation. I was inspired by for the design. So my tool will have a whell for the meseaurement. First problem, I have to find the compromise between precision and size because the precision is directly related to the wheel dimension.
The smaller the wheel, the greater the precision but, the diameter of the wheel must not however be less than the diameter of the shaft of the encoder. The resolution is the circumference of the measuring wheel divided by the resolution of the encoder.
So let's try some example
| Wheel diameter | Circumference | Encoder 256cpr | Encoder 600cpr | Encoder 1000cpr | Encoder 2000cpr |
|---|---|---|---|---|---|
| 15mm | 47.1mm | 0.184 | 0.0785 | 0.0471 | 0.0235 |
| 20mm | 62.8mm | 0.2453 | 0.1047 | 0.0628 | 0.0314 |
| 25mm | 78.5mm | 0.3066 | 0.1308 | 0.0785 | 0.0393 |
| 30mm | 94.2mm | 0.368 | 0.157 | 0.0942 | 0.0471 |
| 40mm | 125.6mm | 0.4906 | 0.2093 | 0.1256 | 0.0628 |
As you can see, the perferct combination is 2000cp encoder with 15mm wheel, but 15mm is too small, I think a good compromise is a wheel with a diameter of 30mm. So I have two chosse for the encoder 1000cpr or 2000cpr. I need to search and compare a price...
- Use STM32 maybe blue pill
- LCD to display the live measure
- Rotary optical encoder > 1000cpr
So, I made my choices for electronics and mechanic.
I've choose NUCLEO board NUCLEO-L412KB, because this board is very small and it's very simple to do test with it because the board integrates the ST-LINK debugger/programmer. The board has STM32L412KBU6U ARM Cortex-M4 core.
For the display, I've chosse an basic i2C lcd with PCF8574T, I chosse this solution because with i2c I've less wire. The wheel will beattached to a rotary optical encoder (1000cpr), bought on AliExpress. And I'll need 3 push buttons, one for function enter/raz, and 2 others for +/-, used to select the saw thickness.
Algorithm is very simple, when the system starts/reset, the user will have to indicates the saw thickness with plus or minus button, when the thickness is good user press on enter/raz button and the loop that measures (wood/stell/plastic...) is start. User has the possibility to raz the measure by pressing enter/raz button.
Stay tuned for update ! :)