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Forum Index : Microcontroller and PC projects : Micromite vers. from matherp 2,2 ohm Resistor
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Plasmamac Guru  Joined: 31/01/2019 Location: GermanyPosts: 596 |
After some hard months with a Rehab iam back in the Backshed  Ive got a stroke in Oktober last Year but fortunately 99 % Symptoms are gone. At the moment i will solder the micromite vga pcb version from Matherp. A quick search on ebay for the 2,2 ohm Resistor in the 3,3v line for the sd card shows bad prices. The other versions in the zip file from Geoffg don’t include the 2,2 ohn in the schematics. Is it really needed? Thx Plasma |
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Mixtel90 Guru Joined: 05/10/2019 Location: United KingdomPosts: 8304 |
You may not need it, it seems to depend on the SDcard. Try a wire link. 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: 9760 |
I tend to always include it on board designs that use the FULL-SIZE SD card. The Trans-Flash(micro-SD) cards don't seem to have that issue, and you can connect them directly. I've never had any issues with TF cards, in other words, NOT using the resistor, but with the full-size SD cards, I often found that without the RC filter, it would cause a spike on the 3v3 line when you insert or remove the card, enough to force a spontaneous and uncommanded reset of the processor. As Mick said above, not every card was an issue, but enough of them WERE an issue, that whenever I use the full-size SD cards now, I automatically include the RC filter, and the problem totally vanishes then. I have settled on 2R2, 10uF and 100n in parallel:  I by no means am suggesting this is the BEST circuit or anything, this just works for me.  Ultimately, try it WITHOUT the RC filter, and if it works for you without issue, you can probably ignore it. Up until you swap SD cards for one that does cause the problem, that is.  Oh, and BTW - welcome back, and I hope you recover well. Smoke makes things work. When the smoke gets out, it stops! |
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| Plasmamac Guru Joined: 31/01/2019 Location: GermanyPosts: 596 |
Thx , i will try a zero ohm bridge. Thx Grogster  Plasma |
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