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Join Date: Aug 2016
Posts: 13

Build RS232 To TTL Converter

10/06/2017 5:01 AM

These days I am researching about how to build RS232 To TTL Converter.I would like to share it here.

Couple of days ago I got a request to update some sort of firmware on a not so typical microprocessor, the LPC2119 type.

As I read many pages on the internet I saw there is a sort of adapter so called “USB to TTL adapter” who can communicate through with the uC. I had not the time to order one but I give a try to make one for the COM port. Actually it is an RS232 to TTL converter which I found better from my opinion than that USB to TTL adapter.

Here is why I like more this RS232 to TTL adapter than the other one:

  • can be used on a real RS232 port
  • it is a stable voltage level converter
  • can be used on USB port too (through USB to RS232 converter)
  • there is no VCC ( somebody would say it’s a disadvantage but wait…) *
  • it is a real hardware stuff, no emulation etc. (if it is used through a real com port)
  • can be built really cheap and easy.

Disadvantages of this device:

  • it’s old school
  • has to use an external power source ( which is actually not bad! )

For what to use such a device?

If you repair electronic where are cpu’s need to be updated the firmware, or you just practicing on some development board where are used some sort of cpu for communicating with the computer, or you maybe can also use it to debugging some sort of data from a desired circuit etc…

Enough talking but go to building one. Here is the schematic what I done and the whole part list to build this simple but usable device.

The schematic is as following:

Part list:

Personally I don’t trust device which use the power from the USB port.

Lot of time I run into trouble, killed eeprom content’s, killed the uC’s firmware’s etc. because a voltage drops on the USB port. The USB port can’t manage more current than 500mA (I talk about the USB 2.0), which is not a small amount but also not enough if on the same USB controller are attached a mouse, scanner etc.

You can run out of power and the USB controller will shut down until you read or write the content to or from the desired device.

Hoping you enjoy this article and will save lot of repair time.

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Guru

Join Date: Apr 2010
Posts: 5628
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#1

Re: Build RS232 To TTL Converter

10/06/2017 10:50 AM

I think this is the datasheet you meant to include:

http://www.ti.com/lit/ds/symlink/max232.pdf

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Engineering Fields - Electrical Engineering - Been there, done that, still doing it. Engineering Fields - Control Engineering - New Member

Join Date: Dec 2008
Location: Long Island NY
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#2

Re: Build RS232 To TTL Converter

10/06/2017 11:25 AM

You forgot about the VCC decoupling capacitor. While you do have short traces I prefer using a ground plane.

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Guru

Join Date: Oct 2008
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#3

Re: Build RS232 To TTL Converter

10/06/2017 4:52 PM

Jestine, I visited your web site. It is very interesting.

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Guru

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#4

Re: Build RS232 To TTL Converter

10/07/2017 3:40 AM

I have just bought a number of converters like the first picture. The benefit of those is that the output signal to the uC is at the same voltage as the power source, so the same device can be used for 5v or 3v3 uCs.

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Guru

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#5

Re: Build RS232 To TTL Converter

10/07/2017 8:33 PM

Thank you for posting the project.

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