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--></style></head><body lang=EN-US link=blue vlink=purple style='word-wrap:break-word'><div class=WordSection1><p class=MsoNormal><b><span style='font-size:11.0pt;font-family:"Calibri",sans-serif'>9 attendees<o:p></o:p></span></b></p><p class=MsoNormal><b><span style='font-size:11.0pt;font-family:"Calibri",sans-serif'><o:p> </o:p></span></b></p><p class=MsoNormal><b><span style='font-size:11.0pt;font-family:"Calibri",sans-serif'>Announcements:<o:p></o:p></span></b></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri",sans-serif'>All Things Open happening now (until 10/14)<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri",sans-serif'>PCB Carolina \u2013 11/12<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri",sans-serif'>Design-2-Part Show \u2013 10/29 & 10/30<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri",sans-serif'><o:p> </o:p></span></p><p class=MsoNormal><b><span style='font-size:11.0pt;font-family:"Calibri",sans-serif'>P.O.T.M.<o:p></o:p></span></b></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri",sans-serif'>From last month\u2019s problem, Shane explained why the P MOSFET in the C3 pico schematic is backwards.<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri",sans-serif'><a href="https://www.wemos.cc/en/latest/_static/files/sch_c3_pico_v1.0.0.pdf">https://www.wemos.cc/en/latest/_static/files/sch_c3_pico_v1.0.0.pdf</a><o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri",sans-serif'>Q1 in the lower left has the body diode in what looks like an always conducting orientation.<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri",sans-serif'>Here is a Falstad simulation of the battery isolation and reverse polarity protection.<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri",sans-serif'><a href="https://www.falstad.com/circuit/circuitjs.html?ctz=CQAgjCAMB0l3BWcAmWDLMgZgBxmcgCxg4CcSCAbCBZDQKYC0YYAUAGYinXIDsyXavhwgsWcNCQwMrAE4hKhEHwGLRlEXTDw4rACaDl-cKQErl4AHIJeLVgHcTZ42FMpNDp+-D5vkT8xCyCKMhCLCUJ5q5txGAv4A5gpKWBrJojhKdP4ASiCMschU+YVEUOUQUuUwCKx5BUK+DSA42eWEdITQEG01rADO+WFx4DzGbewAhgA2-fSsAA6imN5YK1gIAuJt2jq6jq5baWqpHvJFQm4Xyjia4PCeh97XEf6OL8HKxU9vXzy3f3UHnexVOXjB-kwvCG4U+oREsSUADUAEIAQQAKqwoaMRmAeB0QMiUQBVADK2Mg0MCokgShpa06IAAkgA7OayAAuAB1+uSUawyTDvM1XuUprN6OVkHUSkJCPTYmBeNQ2oTQt1qlBJI8xqolOZftcwYygZFHKaTetNubllpPh8PDiwAraUoXSkVkoyQBjAAWAHtOZyANYAT15ABEAJYBvTzIXwkbNQ3imZzaWylMA5qmtV0RhVbI6nFK3xKz5KHL0ABu9Fkcz0vIACowAGIAUSxgxpEWGYroErmnn7n1afkp0Pxoy0QhVRJAzYD9nrvLJ9mjnP9rCAA">https://www.falstad.com/circuit/circuitjs.html?ctz=CQAgjCAMB0l3BWcAmWDLMgZgBxmcgCxg4CcSCAbCBZDQKYC0YYAUAGYinXIDsyXavhwgsWcNCQwMrAE4hKhEHwGLRlEXTDw4rACaDl-cKQErl4AHIJeLVgHcTZ42FMpNDp+-D5vkT8xCyCKMhCLCUJ5q5txGAv4A5gpKWBrJojhKdP4ASiCMschU+YVEUOUQUuUwCKx5BUK+DSA42eWEdITQEG01rADO+WFx4DzGbewAhgA2-fSsAA6imN5YK1gIAuJt2jq6jq5baWqpHvJFQm4Xyjia4PCeh97XEf6OL8HKxU9vXzy3f3UHnexVOXjB-kwvCG4U+oREsSUADUAEIAQQAKqwoaMRmAeB0QMiUQBVADK2Mg0MCokgShpa06IAAkgA7OayAAuAB1+uSUawyTDvM1XuUprN6OVkHUSkJCPTYmBeNQ2oTQt1qlBJI8xqolOZftcwYygZFHKaTetNubllpPh8PDiwAraUoXSkVkoyQBjAAWAHtOZyANYAT15ABEAJYBvTzIXwkbNQ3imZzaWylMA5qmtV0RhVbI6nFK3xKz5KHL0ABu9Fkcz0vIACowAGIAUSxgxpEWGYroErmnn7n1afkp0Pxoy0QhVRJAzYD9nrvLJ9mjnP9rCAA</a><o:p></o:p></span></p><ol style='margin-top:0in' start=1 type=1><li class=MsoListParagraph style='margin-left:0in;mso-list:l0 level1 lfo2'><span style='font-size:11.0pt;font-family:"Calibri",sans-serif'>With VBAT (USB power) off and VBAT at +4.1V, the body diode conducts, but also R8 pulls down the gate which enhances the MOSFET and it conducts.<o:p></o:p></span></li><li class=MsoListParagraph style='margin-left:0in;mso-list:l0 level1 lfo2'><span style='font-size:11.0pt;font-family:"Calibri",sans-serif'>With VBAT (USB power) off and VBAT at -4.1V, the body diode does not conducts, R8 pulls down the gate but the MOSFET is not enhanced since it is higher voltage than VBAT.<o:p></o:p></span></li><li class=MsoListParagraph style='margin-left:0in;mso-list:l0 level1 lfo2'><span style='font-size:11.0pt;font-family:"Calibri",sans-serif'>With VBAT (USB power) at +5 and VBAT at +4.1V, the body diode does not conduct. R8 does not pull down the gate and the MOSFET is not conducting.<o:p></o:p></span></li><li class=MsoListParagraph style='margin-left:0in;mso-list:l0 level1 lfo2'><span style='font-size:11.0pt;font-family:"Calibri",sans-serif'>With VBAT (USB power) at -5 and VBAT at -4.1V \u2026 We did not talk about this case.<o:p></o:p></span></li></ol><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri",sans-serif'><o:p> </o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri",sans-serif'>With the MOSFET installed in the forward direction:<o:p></o:p></span></p><ol style='margin-top:0in' start=1 type=1><li class=MsoListParagraph style='margin-left:0in;mso-list:l2 level1 lfo3'><span style='font-size:11.0pt;font-family:"Calibri",sans-serif'>With VBAT (USB power) off and VBAT at +4.1V, the body diode does not conduct, R8 pulls down the gate which enhances the MOSFET and it conducts.<o:p></o:p></span></li><li class=MsoListParagraph style='margin-left:0in;mso-list:l2 level1 lfo3'><span style='font-size:11.0pt;font-family:"Calibri",sans-serif'>With VBAT (USB power) off and VBAT at -4.1V, the body diode conducts and bad things happen as current flows the wrong way<o:p></o:p></span></li><li class=MsoListParagraph style='margin-left:0in;mso-list:l2 level1 lfo3'><span style='font-size:11.0pt;font-family:"Calibri",sans-serif'>With VBAT (USB power) at +5 and VBAT at +4.1V, the body diode conducts and current flows into the battery.<o:p></o:p></span></li></ol><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri",sans-serif'><o:p> </o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri",sans-serif'>Shane says he has to think through P-FETs over and over and often still gets it wrong on the first try.<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri",sans-serif'><o:p> </o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri",sans-serif'><o:p> </o:p></span></p><p class=MsoNormal><b><span style='font-size:11.0pt;font-family:"Calibri",sans-serif'>Golf Cart caddy robots<o:p></o:p></span></b></p><ul style='margin-top:0in' type=disc><li class=MsoNormal style='mso-list:l1 level1 lfo1'><span style='font-size:11.0pt;font-family:"Calibri",sans-serif'><a href="https://www.amazon.com/vdp/0505b34b64a74ead982bedb9ca697bb2?product=B0CTLQFN7C&ref=cm_sw_cp_r_ib_dt_GqX7TFBSYx1rr">https://www.amazon.com/vdp/0505b34b64a74ead982bedb9ca697bb2?product=B0CTLQFN7C&ref=cm_sw_cp_r_ib_dt_GqX7TFBSYx1rr</a><o:p></o:p></span></li><li class=MsoNormal style='mso-list:l1 level1 lfo1'><span style='font-size:11.0pt;font-family:"Calibri",sans-serif'><a href="https://www.youtube.com/watch?v=bbbB6Q-9d00">https://www.youtube.com/watch?v=bbbB6Q-9d00</a><o:p></o:p></span></li><li class=MsoNormal style='mso-list:l1 level1 lfo1'><span style='font-size:11.0pt;font-family:"Calibri",sans-serif'>6:18 - remote controls<o:p></o:p></span></li><li class=MsoNormal style='mso-list:l1 level1 lfo1'><span style='font-size:11.0pt;font-family:"Calibri",sans-serif'><a href="https://www.youtube.com/watch?v=5md-nI0PLMg">https://www.youtube.com/watch?v=5md-nI0PLMg</a><o:p></o:p></span></li><li class=MsoNormal style='mso-list:l1 level1 lfo1'><span style='font-size:11.0pt;font-family:"Calibri",sans-serif'><a href="https://www.caddytrek.com/wp-content/uploads/2024/09/CaddyTrek-R3X-User-Manual.pdf">https://www.caddytrek.com/wp-content/uploads/2024/09/CaddyTrek-R3X-User-Manual.pdf</a><o:p></o:p></span></li><li class=MsoNormal style='mso-list:l1 level1 lfo1'><span style='font-size:11.0pt;font-family:"Calibri",sans-serif'>Follow Mode<o:p></o:p></span></li><li class=MsoNormal style='mso-list:l1 level1 lfo1'><span style='font-size:11.0pt;font-family:"Calibri",sans-serif'><a href="https://www.youtube.com/watch?v=tWhwjzcx-5E">https://www.youtube.com/watch?v=tWhwjzcx-5E</a><o:p></o:p></span></li><li class=MsoNormal style='mso-list:l1 level1 lfo1'><span style='font-size:11.0pt;font-family:"Calibri",sans-serif'>Marching Mode<o:p></o:p></span></li><li class=MsoNormal style='mso-list:l1 level1 lfo1'><span style='font-size:11.0pt;font-family:"Calibri",sans-serif'><a href="https://www.youtube.com/watch?v=ea1G-qfPW7Y">https://www.youtube.com/watch?v=ea1G-qfPW7Y</a><o:p></o:p></span></li><li class=MsoNormal style='mso-list:l1 level1 lfo1'><span style='font-size:11.0pt;font-family:"Calibri",sans-serif'><a href="https://www.youtube.com/shorts/MUNPBY-ayTA">https://www.youtube.com/shorts/MUNPBY-ayTA</a><o:p></o:p></span></li></ul><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri",sans-serif'><o:p> </o:p></span></p><p class=MsoNormal><b><span style='font-size:11.0pt;font-family:"Calibri",sans-serif'>Nick\u2019s presentation on using RP2040 and ESP32s3<o:p></o:p></span></b></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri",sans-serif'><o:p> </o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri",sans-serif'>2.8\u201d round display with touch screen powered by ESP32S3<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri",sans-serif'><a href="https://www.amazon.com/Waveshare-Capacitive-Development-Dual-core-Processor/dp/B0DMJZPH2R/ref=sr_1_3?crid=305CVAL77KDZK&dib=eyJ2IjoiMSJ9.ZVKSkz9QUp4yDK6bhcSnvHZJQcvEHL62dzudh8NCG8rE-7v8yB-ByEFEVFkDKWV4UT3zd4olONkX225u9U4Zm0Iu1rQbqcMY-KFDw9ZgigkTTabjjze80J9vZrSqwERMOJP_8GwmczaT4rIIUPRg8i6WaNgLizf0hErUPVFZfn2zITWXE2iOXY0jiDAMnuHbFhmAAUx8KhN5v4TEyBAg4fCYkZs8Is_hKjiiscyLf3c.8zceK6_QrPDx1cK6o8u_n4gasPSd7pefuEdBJkyfmJ8&dib_tag=se&keywords=waveshare+esp32-s3+2.8inch+capacitive+touch&qid=1760449294&sprefix=waveshare+esp32-s3+2.8%2Caps%2C100&sr=8-3">https://www.amazon.com/Waveshare-Capacitive-Development-Dual-core-Processor/dp/B0DMJZPH2R/ref=sr_1_3?crid=305CVAL77KDZK&dib=eyJ2IjoiMSJ9.ZVKSkz9QUp4yDK6bhcSnvHZJQcvEHL62dzudh8NCG8rE-7v8yB-ByEFEVFkDKWV4UT3zd4olONkX225u9U4Zm0Iu1rQbqcMY-KFDw9ZgigkTTabjjze80J9vZrSqwERMOJP_8GwmczaT4rIIUPRg8i6WaNgLizf0hErUPVFZfn2zITWXE2iOXY0jiDAMnuHbFhmAAUx8KhN5v4TEyBAg4fCYkZs8Is_hKjiiscyLf3c.8zceK6_QrPDx1cK6o8u_n4gasPSd7pefuEdBJkyfmJ8&dib_tag=se&keywords=waveshare+esp32-s3+2.8inch+capacitive+touch&qid=1760449294&sprefix=waveshare+esp32-s3+2.8%2Caps%2C100&sr=8-3</a><o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri",sans-serif'><o:p> </o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri",sans-serif'>LVGL graphics library is wonderful.<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri",sans-serif'>Trying to control precise timing of DMA while doing LVGL and touch was problematic.<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri",sans-serif'>Solution was to use RP2040 stamp (USB interface is via a removable ribbon cable) to control the timing sensitive stuff.<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri",sans-serif'>I2C was used to pass JSON commands between the two processors.<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri",sans-serif'>EDGER code lives once more.<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri",sans-serif'><o:p> </o:p></span></p><p class=MsoNormal><b><span style='font-size:11.0pt;font-family:"Calibri",sans-serif'>Misc<o:p></o:p></span></b></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri",sans-serif'>Talked about tariff impacts on price and shipping.<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri",sans-serif'>Glen Smith gave away a large quantity of nice watertight boxes with some electronics inside. Buck DC converter and some Bluetooth thing that would be difficult to reverse engineer.<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri",sans-serif'>Paul re-discovered that shields for Arduino boards do not need to cover all of the pins. The lower 4 pins (Gnd, 3v3, 5v, D5) of a D1 mini are all you need for a project with minimal I/O requirements.<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri",sans-serif'><o:p> </o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri",sans-serif'><o:p> </o:p></span></p></div></body></html>