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lali
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Joined: 07/01/2022
Location: United States
Posts: 4

Posted: 06:13pm 07 Jan 2022

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Greetings,

Newbie here. I have successfully configured an SD card and a DHT11. Programmed a dump to linux screen using VT100 escape sequences to format. Boring. I wanted an LCD screen.

I bought a Waveshare pico-LCD-1.3 and a bus expander thinking it would reduce the spaghetti. I can not figure out how to configure OPTION SYSTEM SPI for the SD card and the LCD to work The LCD Reset pin conflicts with MISO on the pico. The LCD has headers that allow direct connection to the rpi pico, so obviously I needed the bus expander. I think I'm going to have to wire from the LCD header to a breadboard to avoid the conflict. Has anyone else seen this?

Thanks for your help,

Larry

matherp
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Joined: 11/12/2012
Location: United Kingdom
Posts: 10617

Posted: 06:22pm 07 Jan 2022

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How are you connecting the SDcard? Flying leads or does it plug to the Pico directly? If the latter post a link so we can see if there is a resolution

If the former then I've just tested it successfully

Edited 2022-01-08 04:55 by matherp

lali
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Joined: 07/01/2022
Location: United States
Posts: 4

Posted: 07:12pm 07 Jan 2022

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Hi Peter,

I'm using flying leads to the SD card.

I really don't understand your use of GP28 in the option system spi statement. That looks like ADC2 and not an spi pin. What am I missing?

I'll try it just as you've shown and report back.

Larry

andreas

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Joined: 07/12/2020
Location: Germany
Posts: 226

Posted: 08:32pm 07 Jan 2022

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Hello Larry,

this is my setup. I have an LCD-screen, DHT sensor, RealTime clock and SDCard reader using a single power supply 5V. The 3.3V are generated by and voltage regulator on the breadboard. I have connected power to the VSYS pin of the pico.

The RTC and the sensor are using 3.3V. The SDCard has it's own voltage regulator to generate 3.3V.

When I want to programm that setup I use PuTTy under Linux and connect an USB cable on the fly. PuTTy shows nice colours when programming within an Edit-session.

> option list
OPTION CPUSPEED (KHz) 133000
OPTION DISPLAY 50, 100
OPTION LCDPANEL ILI9341, LANDSCAPE,GP15,GP14,GP13
OPTION GUI CONTROLS 75
OPTION TOUCH GP12,GP11
OPTION AUTORUN ON
OPTION COLOURCODE ON
OPTION SDCARD GP5, GP2, GP3, GP4
OPTION SYSTEM SPI GP18,GP19,GP16
OPTION SYSTEM I2C GP20,GP21
OPTION RTC AUTO ENABLED

lali
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Joined: 07/01/2022
Location: United States
Posts: 4

Posted: 09:23pm 07 Jan 2022

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Andreas,

Thanks for your reply. I've solved the LCD issue with help from Peter.

Your pictures were very useful and highlighted another problem. I have several of the same SD card adapter that you show. All of mine always fail with error messages which I neglected to write down. I replaced that adapter with one from Adafruit and it works fine. Have you had any issues with your adapter?

Larry

andreas

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Joined: 07/12/2020
Location: Germany
Posts: 226

Posted: 09:59pm 07 Jan 2022

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Hallo Larry,

yes there were problems as long as I tried to use the USB cable from the PC as the single power source. I could read but nut write. Writing "unmounted" the SDCard.

When I started using an external power supply reading and writing was fine.

I think the SDCard needs more power for writing and therefore a good power source.

The advantage of connecting the 5V to VSYS and not to VBUS is, that my external power supply will not source power into the PC because there is a diode between VBUS and VSYS. The pico takes the power which is higher either VBUS from the PC or VSYS from the external source. This way I can connect the USB cable at any time. The pico will continue to run as log as there is external power supply connected.

-andreas

lali
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Joined: 07/01/2022
Location: United States
Posts: 4

Posted: 11:01pm 07 Jan 2022

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Andreas,

Time to dig out the bench supply. I've been relying on USB so long, I'm not sure where it is!

Larry

andreas

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Joined: 07/12/2020
Location: Germany
Posts: 226

Posted: 11:09pm 07 Jan 2022

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Mixtel90

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Joined: 05/10/2019
Location: United Kingdom
Posts: 8298

Posted: 07:45am 08 Jan 2022

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There is very rarely a problem with powering PicoMite stuff from USB. The Pico module is happy at down to less than 2V input on VSYS as the buck-boost SMPS will handle it.

If you happen to be using a laptop with a particularly weak USB supply output it's well worth getting a powered USB hub anyway.

SDcard power often needs filtering because of surges. Try a series resistor of 2R2 from the 3V3 supply and a 50-100uF capacitor, bypassed by 0.1uF, to ground.

Some adapters (particularly some labelled "for Arduino") have series resistors on the signal lines which can cause problems with some cards. It's usually worth avoiding those.

Mick

Zilog Inside! nascom.info for Nascom & Gemini
Preliminary MMBasic docs & my PCB designs

andreas

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Joined: 07/12/2020
Location: Germany
Posts: 226

Posted: 09:44am 08 Jan 2022

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Hello Mick,

Quote Try a series resistor of 2R2 from the 3V3 supply and a 50-100uF capacitor, bypassed by 0.1uF, to ground.

I will do that today, have time over the weekend to play a little. Would be very nice to have USB as the only power supply. Power specs should be ok using USB:

USB 2.0 5 Volt 0,5 A 2,5 W
USB 3.0/3.1/3.2 5 Volt 0,9 A 4,5 W

-andreas
Edited 2022-01-08 19:45 by andreas

JohnS
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Joined: 18/11/2011
Location: United Kingdom
Posts: 4147

Posted: 10:02am 08 Jan 2022

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Has the (pico) device asked for so much?

If not, it will get less and then surges may matter more.

John

Mixtel90

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Joined: 05/10/2019
Location: United Kingdom
Posts: 8298

Posted: 10:33am 08 Jan 2022

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Peter always includes filtering for the SDcard now and it seems to work. :) I've used SDcards without filtering successfully but not every time.

If you reduce the CPU speed on the PicoMite the supply current drops so that could be used to take some load off the USB (but it's not a big difference). I think you can go down as low as
OPTION CPUSPEED = 48000

Demand on the USB doesn't get anywhere close to 500mA unless you have a lot of add-ons.

Mick

Zilog Inside! nascom.info for Nascom & Gemini
Preliminary MMBasic docs & my PCB designs

andreas

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Joined: 07/12/2020
Location: Germany
Posts: 226

Posted: 12:14pm 08 Jan 2022

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Hello Mike,

the low pass filter did solve my SDCard-writing-problem. Many thanks for that hint!
I use two of them. One for 5.0V and one for 3.3V.

I took a different value for the capacitor because I had no 50uF or 100uF here. But seems to be that 10uF will do.

-andreas

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