RS-232 to TTL serial converter using ST232C - Page 1
Forum section: electronics / projects

author: m4rtin
author_rank: Regular Contributor
timestamp: August 09, 2013, 11:15:22 am
content: I boughtST232Cdriver in order to build a RS-232 to TTL serial converter. Scheme, based on the "Typical example"(page 7) inST232C manualandthis example, is following:According toST232C manual, one can use either 0.1uF or 1uF electrolytic capacitors.Is this scheme correct? In addition, how can I identify pin 1 on ST232C? There seems to be no mark identifying this:top view,side view,side viewandbottom viewof ST232C.

author: fcb
author_rank: Super Contributor
timestamp: August 09, 2013, 11:25:37 am
content: Pin 1 is top-left on P1070491.JPG

author: David_AVD
author_rank: Super Contributor
timestamp: August 09, 2013, 11:27:08 am
content: The side with the chamfer is pins 1 to 8.

author: amyk
author_rank: Super Contributor
timestamp: August 09, 2013, 11:31:46 am
content: FYI page 12 of the datasheet shows this.

author: m4rtin
author_rank: Regular Contributor
timestamp: August 09, 2013, 11:54:50 am
content: fcb,David_AVD,amyk: Thanks! I didn't even notice that one side of the chip has the chamfer. However, what about my scheme? Is this correct for ST232C?

author: MrAureliusR
author_rank: Unknown
timestamp: August 09, 2013, 01:31:48 pm
content: It does appear to be correct. Its very similar to the MAX232. Just like the MAX232/A depending on whether its the A model or not determines if you use regular 1uF caps or, if you have the 232A, you use 0.1uF ones. Read the datasheet very closely to be sure which is right for your model or it won't work!

author: m4rtin
author_rank: Regular Contributor
timestamp: August 09, 2013, 02:14:02 pm
content: Quote from: MrAureliusR on August 09, 2013, 01:31:48 pmMy driver chip has "ST232C EZ64720" printed on it. So looks like I don't have the232Amodel? In addition, on a page 12 indatasheet, it says that"C1-4 capacitors can even be 1?F ones". The reason why I prefer 1uF capacitors is that my local electronics shop do not have 0.1uF ones.

author: Unknown
author_rank: Unknown
timestamp: August 09, 2013, 02:20:24 pm
content: An electronics shop that does not have 0.1 uF caps? Really? Note that 0.1 uF = 100 nF, and is about the most popular cap size.

author: m4rtin
author_rank: Regular Contributor
timestamp: August 09, 2013, 02:27:51 pm
content: Quote from: alm on August 09, 2013, 02:20:24 pmAt least at the moment they don't

author: free_electron
author_rank: Super Contributor
timestamp: August 09, 2013, 02:40:28 pm
content: Those capacitors do not need to ne electrolytic ! Just ask for regular 100nF capacitors. They will have those. You could put in 120,150,180,220,270,330,390,470,560,680,820 up to 1uf.The chip doesn't care. It switches slow enough to get where it needs to be.

author: m4rtin
author_rank: Regular Contributor
timestamp: August 11, 2013, 03:42:58 pm
content: 1uF capacitors worked well. I got the RS-232 to TTL serial converter workingHowever, few questions:1) why are capacitors needed for this driver chip?2) how are TTL signals(3.3V) converted to voltages suitable for computer(12V) and the other way around in ST232C?

author: jahonen
author_rank: Super Contributor
timestamp: August 11, 2013, 04:54:37 pm
content: Quote from: m4rtin on August 11, 2013, 03:42:58 pmCapacitors are needed for the internal charge pump which generates higher/negative voltages from 3.3 volt supply to power the RS-232 line drivers. Valid RS-232 voltage levels are at least ±5V at receiver input.Receivers of ST232C are tolerant for RS-232 voltage levels and transmitters perform an inversion and a level shift operation to produce RS-232 levels.Regards,Janne

author: ivan747
author_rank: Super Contributor
timestamp: August 11, 2013, 05:50:48 pm
content: The chip works under the same principle as voltage doublers. You can watch Dave's video on voltage doublers and read how the MAX232 works (they should work more or less the same).