PyBoard v1.1 Power On Boot Problem

[thestumbler]

I'm running a PyBoard v1.1, and have noticed an issue with power-on booting when an SD card is plugged in.

Case 1: No SD card mounted

• Power on, boots to flash

• Reset button, boots to flash

Case 2: SD card installed

• Power on, doesn't "boot", just green light and no REPL <=== PROBLEM

• Reset button, boots to SD card

I worried it might be something with my connected hardware, so I did a test just now with a plain PyBoard with no connected hardware. This doesn't seem to be an issue, I get the same results. Setup is shown below.

Any idea why the board doesn't boot with a power-on reset?

Setup Code

Boot.py is the same on internal flash and sd card:

Code: Select all

# boot.py -- run on boot-up
# can run arbitrary Python, but best to keep it minimal

import machine
import pyb
import uos

uart=pyb.UART(6,115200)
uos.dupterm(uart)

pyb.country('US') # ISO 3166-1 Alpha-2 code, eg US, GB, DE, AU
pyb.main('main.py') # main script to run after this one
#pyb.usb_mode('VCP+MSC') # act as a serial and a storage device
#pyb.usb_mode('VCP+HID') # act as a serial device and a mouse

The two main.py files are similar, but display different LEDs and Hello messages:

pyboard/flash/main.py:

Code: Select all

import pyb
pyb.LED(1).on()
pyb.LED(2).off()
pyb.LED(3).on()
pyb.LED(4).off()
print('HELLO from FLASH')

pyboard/sd/main.py:

Code: Select all

import pyb
pyb.LED(1).off()
pyb.LED(2).on()
pyb.LED(3).off()
pyb.LED(4).on()
print('HELLO from SD')

[thestumbler]

Found my problem. My +5V power supply turn-on was slower than the time constant of the reset RC circuit on the Pyboard. I've temporarily tacked on a larger capacitor (47 uF, way too big, just to test the solution). I will either add a more suitable capacitor on my carrier board, or put a MCP120.

[sim222]

Found my problem. My +5V power supply turn-on was slower than the time constant of the reset RC circuit on the Pyboard. I've temporarily tacked on a larger capacitor (47 uF, way too big, just to test the solution). I will either add a more suitable capacitor on my carrier board, or put a MCP120.

thanks for your self answer~~

[thestumbler]

One last remark on this. While still prototyping with my system, I had tacked on temporarily a MCP-120 supervisory reset chip. I had almost forgotten about it, and a couple of days ago my board started acting strange again. For some time I thought the SD card was bad, but finally I found that one wire of my temporary hack had broken off. I soldered one down more permanently this time, and covered it up with UV-curing glue.