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.
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