I own a bunch of USB to serial debug board based on CH340G/T or PL2303HX, and all include a crystal on the board with the exception of Hardkernel’s USB-UART module kit based on CP2104 (QFN24 package) working without crystal, hence smaller than most, but a bit more expensive than most.
WCH has just released a new form version of their CH340 that does not require a crystal, comes in a tiny (3x3mm) MSOP10 package, and costs about 42 cents on Electrodragon (5 pieces). You’ll also find it for as low as 1 CNY ($0.15) on 1688.com.
CH340E is slightly more expensive than CH340G, but considering you don’t need a crystal, and it will take less space on your PCB, total BoM cost for this USB to TTL function should be lower. Electrodragon reports that only two external parts are required, and they tested it up to 150,000 baud to flash ESP8266. CH340E is software compatible with CH340G, so the same drivers will work, and most of the electrical characteristics are the same, as you can find out in the product page.
The board above just measures 16×16 mm, and sells for $0.99 + shipping. In my case, shipping is $1.47, but I’d except that to soon go away, as some other CH340E boards go for just $1.01 shipped. Some CH340G boards are even cheaper, but the main point is that you can now add USB to serial to your design with minimal cost and area.
Thanks to Zoobab for the tip.
Jean-Luc started CNX Software in 2010 as a part-time endeavor, before quitting his job as a software engineering manager, and starting to write daily news, and reviews full time later in 2011.
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“ElectroGarDon” got my attention. A new store I do not know? I clicked and immediately saw it was just a typo.
Nice affiliation trick 😉
One quick way to reduce cost on that board is to get rid of the polyfuse. On the other side, it’s great to see a polyfuse in such a cheap board. Safety, people!
Also CH340C which is pin-to-pin compatible with CH340G but doesn’t require crystal.
My favorite is Holtek HT42B534-1 (http://www.holtek.com/productdetail/-/vg/42B534-x) which doesn’t require crystal, doesn’t require drivers (implements standard cdc acm class) and costs the same as CH340* chips. It’s even comes with internal EEPROM which allows to set custom vid/pid/product name!
Cheap PL2303 flash my esp-07 surprisely really fine at full speed 1 500 000 baud. It make no error unlike at 115200baud.
I think there is an divider of frequency not enough occurate to working fine in the range over 56700 to 1500000.
Occurate quartz is needed for serial link without big error rate
Pinheader has another pinout than “standard” USB-Serial converters with “FTDI” chips.
@Evgeny
HT42B534-1 looks nice (though 1μF electrolytic capacitor on application schematic suggests that internal regulator may hace stability problems with ceramics 🙁 ).
Any idea where to buy it (ouside China)? Nothing on octopart/findcips/aliexpress; ebay search finds lots of brassieres, zero chips.
We buy it on lcsc.com . Although it’s still Chineese website they deal with international customers just fine.