USB to serial cable that work, sometimes. A possible fix

[Born2BeWired]

I bought a USB to serial cable converter from e-gizmo and one of their engineers engaged me in a conversation regarding some problems they encountered with this device. This may be of interest to you since a lot of us experimenters got a need for this type of cable, and you may already have one with similar problem (not necessarily from e-gizmo).

Apparently, when e-gizmo shopped for this cable, they had several choices coming from different manufacturers. They picked the one with the higher price tag for the following reasons- It employs the immensely popular prolific chipset PL2303, not some chip hidden under a black epoxy blob; better overall workmanship, and perhaps a very important criteria, it is serviceable.



The case can be opened without destroying anything, and the PCB is constructed in a familiar (SMD components) way. According to e-gizmo, the samples they had work splendidly during their tests.



But reports of troubles started to pour in as soon as a few dozens were sold; troubles that range from dropping connections, to no functions at all. E-gizmo engineers took a second look at the guts of the cable and found something they missed on the initial evaluations: the USB cables used CERAMIC RESONATOR  instead of crystal!!! 



Ceramic resonators makes cheaper alternatives for crystal, but has wide tolerance spread and mediocre tempco. That makes them unsuitable for circuits requiring tight tolerance timings, such as this USB to serial bridge.

Fortunately, the fix to this problem is simple and straightforward- replace the 12MHz ceramic resonator with 12MHz crystal. The USB to serial cable worked flawlessly after the fix was made.



Worth noting at this point: I also had a conversation with Prof. Mike Abundo of U.P. IRC lab about a week later and learned they encountered similar problem, solved with exactly the same fix.

So if you have a USB to serial cable you are about to trash, Huwag muna! If it can be opened for servicing, this fix may work for your cable.

P.S. Kung bibili kayo ng USB to serial cable sa egizmo, tanong nyo muna kung napalitan na ng crystal

[RiDdLeR???]

Just a question, arent those ceramic resonators supposed to be 3-pinned?  At least all the 4Mhz  and 20 MHz ceramic resonators I have are 3-pinned (or maybe they are not ceramic?)

Do you also know what chip is used for the ttl-rs232 conversion for the e-gizmo dongle?

[paranz]

@alyas



yung naka-mark na footprint is xtal oscillator. Baka meron na talaga dalawang loading capacitor yan, pero resonator lang ang nilagay instead na xtal oscillator.

Bubuksan ko rin itong USB2serial converter ko para macheck muna at makahanap na rin ng 12 mhz xtal. 


@sir B

thanx po for the info 

[RiDdLeR???]

Did a quick research, meron pala mga 2-pinned ceramic resonator.  Ano kaya ang equivalent circuit diagram nito?  Yung mga 3-pinned resonator kasi, the equivalent circuit diagram is equivalent to a xtal and 2 loading caps.  So for a 2-pinned siguro, the caps are not grounded anymore.

[Ikasamoko]

Ceramic resonators has 3pins...and has a built in capacitors inside..center pin is connected to gnd..

yung sa image 2 pins lang..baka low quality na xtal lang yan?

ako i preferred ceramic resonator to minimized parts count and simplified pcb layout..so far wala naman sablay yung 3pins na resonator na gamit ko..

[paranz]

^ gusto talaga makamura ng mga chinese.. kaya pati oscillator pinapalitan

[macky]

baka ang q.c. nila(chinese) "once na-detect sa pc, OKEY NA!" pasado na sa quality! hehehe

[paranz]

hehe oo nga

[maldihtah13]

Bakit kya hindi ftdi ang pinili nila?

[paranz]

i think mas mura kasi ang PL2303 chips, para affordable.. P216 lang yung isang cable so ok na ok na rin

[maldihtah13]

makabili pala sa kanila kasing mas mura keysa cdrking

[marcelino]

alam nyo, dapat magcontribute din dito ang egizmo... hehehe... dami na nilang, advertisment dito ah... hehehe

any way, naghahanap din ako ng maganda pero murang serial to USB. salamat sa information, konting tweak lang pala, ok na.

[paranz]

i think meron din PL2303 chips sa e-gizmo..

hmm makagawa rin nga ng USB module tulad nung sa FTDI 

[macky]

any way, naghahanap din ako ng maganda pero murang serial to USB. salamat sa information, konting tweak lang pala, ok na.

serial to USB? meron na po bang ganyan? or nagbaligtad lang ang post ninyo?
di ba mabagal ang serial compared sa USB? kung meron man, anong USB device ang kayang i-support ng speed nito?

[paranz]

USB-to-serial actually ang tamang term

[macky]

yup!!!

from USB converted to SERIAL port, para serial devices ang ico-connect mo.
marami kasing mobo ngayon na USB ports na lang, wala na sa design nila ang serial ports kaya kailangan natin nitong usb-serial converter.

[Winterburn]

Bakit kapag ginagamit ko yung USB-to-Serial cable ko for programming, ayaw gumana? Tinest ko rin yung pins ng USB to Serial ko, walang voltage readings whatsoever. Pero gumagana naman talaga yung cable ko na yun. Sa programming lang talo.

Serial kasi yung programmer ko eh, eh pano pag laptop gamit ko, o di patay-patay na.. Hahaha.

[rdpzycho]

madalas mababa kasi output voltage nila (+5/-5 yung sa akin whereas nasa range ng +12/-12 ang nasa specs ng RS232, IIRC), hindi pwede kung kailangan ng programming voltage nung circuit na galing sa RS232 port.

[maldihtah13]

Bakit kapag ginagamit ko yung USB-to-Serial cable ko for programming, ayaw gumana? Tinest ko rin yung pins ng USB to Serial ko, walang voltage readings whatsoever. Pero gumagana naman talaga yung cable ko na yun. Sa programming lang talo.

Serial kasi yung programmer ko eh, eh pano pag laptop gamit ko, o di patay-patay na.. Hahaha.

try to build those na may external power supply.

[100407]

meron akong ganan na usb to serial.nagloloko din minsan.pinalitan ko lng din ng oscillator ung resonator from my old card reader i bought from cd rking  and it works perfectly!.. . . .thanks bossing