ben/ObsidianVault
1
0 Fork 0
Code Issues Pull Requests Actions Packages Projects Releases Wiki Activity

vault backup: 2026-07-01 18:20:08

Browse Source
This commit is contained in:
ben committed 2026-07-01 18:20:08 -07:00
1 parent fdc45e862f
commit c8b0adc856
1 file changed
+3 -3
Download Patch File Download Diff File Expand all files Collapse all files
PCB Design/Music Player/Process.md
+3 -3
View File
@@ -48,9 +48,9 @@ The display controller gives the option of using SPI or parallel RGB to control
### Backlight Resistors
To limit the current of the backlight for the display series resistors are needed for the anode (power supply) pins. To calculate the value for the resistor the equation
$$R = \frac{{V_{in} - V_{f}}}{I_{f}}$$
is used which gives the current limiting resistor needed for a LED. The display used has a LED voltage of 3.0V and will be supplied with 3.3V. It also typically draws 160 mA of current. Plugging in these values gives
$$R = \frac{{3.3 - 3.0}}{0.16} = 1.875 \Omega$$
For a standard value a $2.0 \Omega$ resistor will be used. This may make the display a little bit less bright but won't change it very much.Vs - Vf) / If using the maximum forward voltage:
is used which gives the current limiting resistor needed for a LED. The display used has a LED voltage of 3.0V and will be supplied with 3.6V (from the buck-boost). It also typically draws 160 mA of current. Plugging in these values gives
$$R = \frac{{3.6 - 3.0}}{0.16} = 3.75 \Omega$$
For a standard value a $3.7 \Omega$ resistor will be used. This may make the display a little bit brighter but won't change it very much. The 3.6V power rail is used to give more buffer for variations in the forward voltage of the backlights. Even though the typical forward voltage is 3.0V it can range from 2.7V to 3.4V and having a larger difference between $V_{in}$ and $V_{f}$ means that manufacturing variations won't affect the brightness and current draw of the display as much. It will also pull the load of the display off of the LDO and put it onto the buck-boost converter that can output much more current.
### Backlight Control
Since this device will be battery-powered and the display is not needed most of the time it needs to be able to be controlled by software by the ESP32-S3. To do this a transistor will be added to the cathode pins to control the backlight with an io pin from the microcontroller.
I chose [this mosfet](https://www.digikey.com/en/products/detail/infineon-technologies/IRLML2502TRPBF/811439) since it has very low resistance and should turn off and on with the 3.3V logic levels of the ESP32-S3.