9 attendees
Announcements: All Things Open happening now (until 10/14) PCB Carolina – 11/12 Design-2-Part Show – 10/29 & 10/30 P.O.T.M. >From last month’s problem, Shane explained why the P MOSFET in the C3 pico >schematic is backwards. https://www.wemos.cc/en/latest/_static/files/sch_c3_pico_v1.0.0.pdf Q1 in the lower left has the body diode in what looks like an always conducting orientation. Here is a Falstad simulation of the battery isolation and reverse polarity protection. https://www.falstad.com/circuit/circuitjs.html?ctz=CQAgjCAMB0l3BWcAmWDLMgZgBxmcgCxg4CcSCAbCBZDQKYC0YYAUAGYinXIDsyXavhwgsWcNCQwMrAE4hKhEHwGLRlEXTDw4rACaDl-cKQErl4AHIJeLVgHcTZ42FMpNDp+-D5vkT8xCyCKMhCLCUJ5q5txGAv4A5gpKWBrJojhKdP4ASiCMschU+YVEUOUQUuUwCKx5BUK+DSA42eWEdITQEG01rADO+WFx4DzGbewAhgA2-fSsAA6imN5YK1gIAuJt2jq6jq5baWqpHvJFQm4Xyjia4PCeh97XEf6OL8HKxU9vXzy3f3UHnexVOXjB-kwvCG4U+oREsSUADUAEIAQQAKqwoaMRmAeB0QMiUQBVADK2Mg0MCokgShpa06IAAkgA7OayAAuAB1+uSUawyTDvM1XuUprN6OVkHUSkJCPTYmBeNQ2oTQt1qlBJI8xqolOZftcwYygZFHKaTetNubllpPh8PDiwAraUoXSkVkoyQBjAAWAHtOZyANYAT15ABEAJYBvTzIXwkbNQ3imZzaWylMA5qmtV0RhVbI6nFK3xKz5KHL0ABu9Fkcz0vIACowAGIAUSxgxpEWGYroErmnn7n1afkp0Pxoy0QhVRJAzYD9nrvLJ9mjnP9rCAA 1. 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. 2. 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. 3. 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. 4. With VBAT (USB power) at -5 and VBAT at -4.1V … We did not talk about this case. With the MOSFET installed in the forward direction: 1. 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. 2. With VBAT (USB power) off and VBAT at -4.1V, the body diode conducts and bad things happen as current flows the wrong way 3. With VBAT (USB power) at +5 and VBAT at +4.1V, the body diode conducts and current flows into the battery. Shane says he has to think through P-FETs over and over and often still gets it wrong on the first try. Golf Cart caddy robots * https://www.amazon.com/vdp/0505b34b64a74ead982bedb9ca697bb2?product=B0CTLQFN7C <https://www.amazon.com/vdp/0505b34b64a74ead982bedb9ca697bb2?product=B0CTLQFN7C&ref=cm_sw_cp_r_ib_dt_GqX7TFBSYx1rr> &ref=cm_sw_cp_r_ib_dt_GqX7TFBSYx1rr * https://www.youtube.com/watch?v=bbbB6Q-9d00 * 6:18 - remote controls * https://www.youtube.com/watch?v=5md-nI0PLMg * https://www.caddytrek.com/wp-content/uploads/2024/09/CaddyTrek-R3X-User-Manual.pdf * Follow Mode * https://www.youtube.com/watch?v=tWhwjzcx-5E * Marching Mode * https://www.youtube.com/watch?v=ea1G-qfPW7Y * https://www.youtube.com/shorts/MUNPBY-ayTA Nick’s presentation on using RP2040 and ESP32s3 2.8” round display with touch screen powered by ESP32S3 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 LVGL graphics library is wonderful. Trying to control precise timing of DMA while doing LVGL and touch was problematic. Solution was to use RP2040 stamp (USB interface is via a removable ribbon cable) to control the timing sensitive stuff. I2C was used to pass JSON commands between the two processors. EDGER code lives once more. Misc Talked about tariff impacts on price and shipping. 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. 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.
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