diff --git a/README.md b/README.md index d31070b975590a4d9e9a795a687c0b12ce2db6b9..e693d283d36e41c2b7d31ecfb781a3a57e69f93e 100644 --- a/README.md +++ b/README.md @@ -90,12 +90,15 @@ The microcontroller can boot in different modes, similar to how you can enter th ### 6) Crystal -The crystal will resonate at a specified frequency. Its waveform will be used as an input to the PLL (Phase Locked Loop) that will multiply the crystal’s frequency. This is the crystal that will be used: https://www.elfa.se/en/quartz-surface-mount-12mhz-iqd-lfxtal003210/p/17452154 +The crystal will resonate at a specified frequency. Its waveform will be used as an input to the PLL (Phase Locked Loop) that will multiply the crystal’s frequency. This is the crystal that will be used: https://www.elfa.se/sv/kristall-ytmontering-16mhz-iqd-lfxtal029370/p/30131284 + +The crystal and its associated capacitors are part of a "Pierce oscillator" circuit connected to two special pins on the MCU - `PH0 - OSC_IN` and `PH1 - OSC_OUT`. To calculate value of the load capacitors required for proper operation, use the following formula: +`C = 2*(Cload - Cstray)` where `Cload` is the load capacitance value specified in the crystal's [datasheet](https://www.elfa.se/Web/Downloads/_t/ds/LFXTAL029370REEL_eng_tds.pdf) (18pF) and `Cstray` is the stray capaciatance on the PCB, usually in the range of 2-10pF (pick something in-between, like 6pF). This gives us a capacitance value of `2*(18 - 6) = 24pF`. The closest standard value would be `22pF`. - Click on the Place component button. - Find the device/Crystal. -- Place it close to `PH0` and `PH1`, pin 5 and 6 (`RCC_OS_CIN` and `RCC_OSC_OUT`). -- Connect the component with wires to the mentioned pins. Value 12MHz. +- Place it close to `PH0 - OSC_IN` and `PH1 - OSC_OUT`, pin 5 and 6. +- Connect the component with wires to the mentioned pins. Value 16MHz. - Connect one 22pF capacitor to each pin on the crystal and connect the other end of the capacitors to GND. ### 7) Serial Wire Debug (SWD) connector @@ -128,7 +131,7 @@ Download the general [datasheet](https://www.pixart.com/products-detail/4/PMW338 For some components (like the PMW3389DM-T3QU) there might not exist a pre-made library, so you will now learn how to draw your own component. - Click on Tools/ Symbol Library Editor. -- Create a new library for your project and click on Create New symbol inthe new library). +- Create a new library for your project and click on Create New symbol in the new library). - Component name ”PMW3389”. OK. - Add pins and name them according to the datasheet. Remember to assign the correct pin number as well. - Make sure to set the ”Electrical type” on each pin according to usage (signal in/out, power in/out etc.) `X` marks a non connected pin. In our setting we don't use `GPO` so you can set it `X`. @@ -139,7 +142,7 @@ Hint. Never, never ever, change the grid settings when placing the pins in the s ### 11) 1.9v Power Supply -As you can see in the PWM3389DM-T3QU datasheet and reference schematics, the sensor requires a 1.9v power supply. This is much less common voltage for a fixed output LDO (try finding one from Elfa or rs-online and you will likely fail). +As you can see in the PWM3389DM-T3QU datasheet and reference schematics, the sensor requires a 1.9v power supply. This is a much less common voltage for a fixed output LDO (try finding one from Elfa or rs-online and you will likely fail). To that end, you can use an adjustable voltage regulator, such as [MIC5235YM5-TR](https://www.elfa.se/en/ldo-voltage-regulator-24-20v-sot-23-microchip-mic5235ym5-tr/p/30099685), which will let you set your desired output voltage using external resistors. @@ -196,11 +199,11 @@ It is very important that the pin numbering on your component is correct to the ### 17) Electric Rule Check (ERC) -ERC is a check that detects if you have any ”lose ends”, meaning that it will give you a warning if you have a net with only one connection. It will also give you a warning if you have drawn a net to a component but the net and the component haven’t connected. To get the ERC to work as intended, you have to mark all the unused pins with a Not-connected flag, found to the right. +ERC is a check that detects if you have any ”loose ends”, meaning that it will give you a warning if you have a net with only one connection. It will also give you a warning if you have drawn a net to a component but the net and the component haven’t connected. To get the ERC to work as intended, you have to mark all the unused pins with a Not-connected flag, found to the right. - 1. ”Perform electrical rules check” button (Ladybug button). - 2. Do a ERC. -- 3. Fix errors.4. +- 3. Fix errors. - 4. Repeat point 1 until errors == 0 && warnings == 3. The GND net is not connected to a Power output, the 5 voltage neither and the capacitor connected to VCAP1 is not connected to a power output. ## First Submission