[TriEmbed] Summary of 10/13/25 Meeting

Wed Oct 15 09:36:58 CDT 2025

Paul,

This is a fabulous set of minutes from Monday's meeting.  Thank you for 
preparing and sending it out.  Was this a one-off effort or something 
you (or someone) does regularly?  I don't want to place undue onus on 
anyone, but this sure was a great chunk of info to receive since I'm 
routinely unable to attend the meeting.

Cheers,
-Brian

On 10/14/25 10:17, The MacDougals via TriEmbed wrote:
> *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 
> <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 <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&ref=cm_sw_cp_r_ib_dt_GqX7TFBSYx1rr <https://
>     www.amazon.com/vdp/0505b34b64a74ead982bedb9ca697bb2?
>     product=B0CTLQFN7C&ref=cm_sw_cp_r_ib_dt_GqX7TFBSYx1rr>
>   * https://www.youtube.com/watch?v=bbbB6Q-9d00 <https://
>     www.youtube.com/watch?v=bbbB6Q-9d00>
>   * 6:18 - remote controls
>   * https://www.youtube.com/watch?v=5md-nI0PLMg <https://
>     www.youtube.com/watch?v=5md-nI0PLMg>
>   * 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>
>   * Follow Mode
>   * https://www.youtube.com/watch?v=tWhwjzcx-5E <https://
>     www.youtube.com/watch?v=tWhwjzcx-5E>
>   * Marching Mode
>   * https://www.youtube.com/watch?v=ea1G-qfPW7Y <https://
>     www.youtube.com/watch?v=ea1G-qfPW7Y>
>   * https://www.youtube.com/shorts/MUNPBY-ayTA <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 <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.
> 
> 
> _______________________________________________
> Triangle, NC Embedded Interest Group mailing list
> 
> To post message: TriEmbed at triembed.org
> List info: http://mail.triembed.org/mailman/listinfo/triembed_triembed.org
> TriEmbed web site: https://TriEmbed.org
> To unsubscribe, click link and send a blank message: mailto:unsubscribe-TriEmbed at bitser.net?subject=unsubscribe
> Searchable email archive available at https://www.mail-archive.com/triembed@triembed.org/
> 