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Forum Index : Microcontroller and PC projects : PICO PicoMite SD CARD reader
| Author | Message | ||||
| bobpitt Newbie  Joined: 18/08/2022 Location: AustraliaPosts: 2 |
I am trying to get a SPI SD CARD reader working under PicoMite. The PICO is not seeing the card reader, until I touch the cap and two resistors near the voltage level adjuster chip. If I run a "files" command, the error message is "Error : SD Card not found". I soon as I touch the cap and two resistors or the voltage level adjuster chip, MM.INFO(SDCARD) shows "READY" and it works fine until I power cycle the PICO. I have the same problem on two PICOs, three SD Card readers powered from two different computers. I am using these SD card readers, https://www.ebay.com.au/itm/304245536610?var=603337606526. I have tried pull up resistors on the four data leads, MISO, MISI, SCK and CS, pull down resistors, plus filter and decoupling caps on the 5V line but no joy. Any suggestions? Edited 2022-08-18 14:22 by bobpitt |
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andreas Senior Member  Joined: 07/12/2020 Location: GermanyPosts: 187 |
OPTION CPUSPEED 100000 does sometimes wonders. -andreas |
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Grogster Admin Group  Joined: 31/12/2012 Location: New ZealandPosts: 9043 |
Hi. Welcome to the forums.  You don't need to level-shift SD cards on the PM, just directly connect as the SD card or Micro-SD card is a 3v3 device, and so is the PM. Perhaps try something like this instead. I've hooked up a few SD cards to PM's now, and I just directly connect them with no level-conversion, or even series resistors. I have no idea what the converter chip is on that module, but you don't need to level-shift anyway, so I would just directly connect using one of the modules I linked to. If you have more then one of those boards, try another one, as it seems a bit temperamental if you can touch it and it works. Perhaps a faulty board? Smoke makes things work. When the smoke gets out, it stops! |
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Mixtel90 Guru  Joined: 05/10/2019 Location: United KingdomPosts: 5705 |
There's no guarantee that those card readers will work. They are designed for use on a 5V system, not a 3V3 system like the PicoMite. The supply voltage for them is intended to be 4V5 to 5V5 and they have an on-board regulator to feed the SD card. They also have level shifters to convert 5V control signals to 3V3 for theSDcard. Sometimes you can find regulated cards that will work, but it's a gamble. Mick Zilog Inside! nascom.info for Nascom & Gemini Preliminary MMBasic docs & my PCB designs |
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| Grogster Admin Group Joined: 31/12/2012 Location: New ZealandPosts: 9043 |
That's a good point, Mick. The boards might actually be converting the 3v3 card voltages, up to 5v. Connecting that to the PM would not be a good idea, as they are not 5v tolerant. Smoke makes things work. When the smoke gets out, it stops! |
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| Mixtel90 Guru Joined: 05/10/2019 Location: United KingdomPosts: 5705 |
If VCC is connected to 3V3 then it won't cause a problem, but due to the volt drop of the regulator there may not be enough voltage to power the SD card. The level shifters will almost certainly only be simple MOSFET circuits on the chip. Some LDO regulators have a sort of "straight through" mode when you get to their drop-out point. The output is then approximately the same as the input voltage, but it's no longer regulated. I *think* there are also some where the output simply fails at drop-out point. One of those would be completely unsuitable. Mick Zilog Inside! nascom.info for Nascom & Gemini Preliminary MMBasic docs & my PCB designs |
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| bobpitt Newbie Joined: 18/08/2022 Location: AustraliaPosts: 2 |
Thanks Andreas, it worked a treat. All I have to do after setting the cpuspeed is run a "print mm.info(sdcard)" and it works perfectly. |
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| JohnS Guru Joined: 18/11/2011 Location: United KingdomPosts: 3649 |
Please someone explain why! John |
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| matherp Guru Joined: 11/12/2012 Location: United KingdomPosts: 8566 |
Because the inappropriate SDcard module is messing the signals to the extent that slowing them down makes it work. THIS IS A REALLY BAD SOLUTION As others have said connect the SDcard socket without any intervening electronics |
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| Mixtel90 Guru Joined: 05/10/2019 Location: United KingdomPosts: 5705 |
I've not tried it, but shorting the input to output on the voltage reg and powering VCC at 3V3 *might* work. It will depend on the characteristics of the MOSFET circuits on the level shifter chip. Personally I'd look for a "straight through" connected module. Mick Zilog Inside! nascom.info for Nascom & Gemini Preliminary MMBasic docs & my PCB designs |
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| JohnS Guru Joined: 18/11/2011 Location: United KingdomPosts: 3649 |
Peter - thanks John |
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stanleyella Guru Joined: 25/06/2022 Location: United KingdomPosts: 1639 |
new user but got ili9341 lcd working and it reads the sd card fine. no card and it says sd card not found. with empty sdcard it says a: no files or sother info. Point is it seems to work with me doing nothing...as it is all new to me. Is the ili9341 sd card socket a usable sd card reader or is it just for the lcd? Sorry if this seems a silly question. I have not got to files yet. |
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| Mixtel90 Guru Joined: 05/10/2019 Location: United KingdomPosts: 5705 |
The SD card socket on the ILI9341 is just a standard socket, but there are small series resistors in series with MISO and MOSI. That prevents *some* cards working properly. I've only had problems with one particular make and model. You have to connect it just as a normal one. It shares the 3V3 supply from the display regulator and has a common ground, of course. I connected it on my Backpack pcb and it's fine. Mick Zilog Inside! nascom.info for Nascom & Gemini Preliminary MMBasic docs & my PCB designs |
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