LC29HAAMD returning garbage data in Serial

Hello, I’m using LC29H(AA) module with UART connection (D_SEL1=0, D_SEL2=0) but every seconds I receive garbage data like this:


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"GŽ[V‡&.´6.6.Ž&›(òi™‘i.Ö0HaH(Ö.a,qaÖ..ÖÖ.â&‡GQ(.©™Áq‰Èq±,\..l6.p;0q<0L&.Ž&WJ9hA Ò,ËE劈..ˆI…ây,\IlG%.§Lˆ,0–a™aq(a(aÖ..(.ˆGÍ.&‡GQ,.©™Éq.…‘°¹,\..L&.p;00x8.l6OL[+rЃ.&–ÉE劈..ˆI…ˆ‰…ˆÉ…ÈŠš"i.aéO8.É2,a‰ÖG.=Ö..ˆ.&‡GQ,.©¡q.…‘°¹,\..L6.p;00x8.l6OL[)r:ƒ…"GŽ[V‡&.´&.&.Ž&.‹&Oj#Q,aq.q20É20É20É2.(aÖa.‘“&‡GQNƒ&0p86tL.…‘arÄbÂa°qa.¹‰Áaâqq,¦-1uÃaHŠÉE劈..ˆi…ˆ‰…ˆé…ÈŠ."i&Aaq(që(....aaÖG.W.&‡GS(.©¡‘q.…‘arÄbÂa°qa.¹‰Áaâqq,¦)3vC!HŠËE劈..ˆI…ˆ‰…ˆÉ…ÈŠš"i.é0aÂaÖ.q.(.,(.a(Ö.a.Qˆq&GŽYNƒ&0p86t#.…‘arÄbÂaaÂa±‰Áaâqq,¦-˜QH.Ó4ÉE劈..ˆI…ˆ‰…ˆé…â¥.‰i.™é0(,.q,ˆY0iaÖ...&‡GQ,.©¡¡q.…2.Wl&.L&.L87pLžaÂqq,¦-˜..
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I see some repeating patterns in there. I’m using 115200 baudrate, without changing any configuration of the module (tried all other baudrates but only 115200 has some meaningful patterns). The hex view is also meaningless.
I followed the reference design approach to design the level shifter with transistors between 3.3v MCU and LC29HAAMD.

115200 is correct one but for the ttl–>usb conv. w is the driver and chip?

FT232RL. I use this for serial connection to another module using the same mcu too, and it works fine.
The transistor I used for level shifting is BC817 (100Mhz). Schema exactly like reference design v1.4

I’m very sorry we can’t
post freely…
I ask the moderators to intervene otherwise this forum becomes only a repository.
However, it would be useful to check first the module directly with a different (ch or pl) adapter connected separately or through an mcu, for example an esp or stm from which you already have a functioning, but individually, that is only the module excluding other connections and only then having completed finally the configuration.
Rely on this sch.
LC29H原理图.pdf (203.7 KB)
and
Quectel_LC29H_Series_Reference_Design_V1.2.pdf (457.7 KB)

1 Like

Thank you so much, I tried it and it works now! So basically you connected TXD1 with 1k resistor and RXD1 with a resistor voltage-divider (5.6k, 1k) to convert 3.3v to 2.8v, instead of a transistor/diode level shifter. Too bad that the official reference design level shifter is either wrong or doesn’t work for me.
Thanks

Not me but Mozihao done the sch…
But be aware that as @splee & oth. has revealed issues also…
Saluti