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I have an atmega32 and a FUM DCF-U atomic clock (signal receiver and decoder) of HKW-elektronik. The µ-controller works with 5V and the module on 3.3V.

I have to build a converter, because the µ-controller only has serial-bus communication and the module has RS232 communication.

I did some research and I found these IC's: MAX232, MAX3323E or MAX3232. In the datasheets and on ArduinoSoftwareRS232 reads that it needs extra voltages (one + and one -) for some pins. Is this necessary or are the capacitors enough? And which IC should I use? (First time I need to use these IC's)

And can these IC's being used without a logic voltage converter?

Thanks in advance

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  • \$\begingroup\$ I use the MAX232, and 4 0.1milifarad ceramic capacitors. It works fine for my uses. \$\endgroup\$ – Eminem May 29 '15 at 12:06
  • \$\begingroup\$ In the datasheet in figure 4. You have to put 8.5V on the 2 and 6 pins. Is this necessary? And do I need a logic level controller between the converter (attached to the µ-controller, 5V) and receiver (3.3V)? \$\endgroup\$ – Daan Mouha May 29 '15 at 12:11
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    \$\begingroup\$ (I use 1microfarad and not 0.1mili as i mentioned above) I dont connect 8.5V to those pins. Just the capacitors, which are connected to the ground as well. My Vcc is connected directly to 5V without a capacitor there. Though i do have a decoupling capacitor between vcc and the common ground. \$\endgroup\$ – Eminem May 29 '15 at 12:17
  • \$\begingroup\$ This is very helpfull. Now my module uses 3.3V for VCC. Is this a problem for the RS232 communication voltage levels? \$\endgroup\$ – Daan Mouha May 29 '15 at 12:19
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    \$\begingroup\$ MAX232 is used to convert TTL voltage levels into RS232 ones. TTL means 5v and 0v, and my RS232 are -9v and +9v. The MAX232 "flips" and amplifies voltage levels. But im not a big expert, so il suggest you will wait for others to say their opinions. \$\endgroup\$ – Eminem May 29 '15 at 12:21
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Answer has been given by Eminem, see his comments below:

Eminem

I use the MAX232, and 4 0.1milifarad ceramic capacitors. It works fine for my uses.

Me

In the datasheet in figure 4. You have to put 8.5V on the 2 and 6 pins. Is this necessary? And do I need a logic level controller between the converter (attached to the µ-controller, 5V) and receiver (3.3V)?

Eminem

(I use 1microfarad and not 0.1mili as i mentioned above) I dont connect 8.5V to those pins. Just the capacitors, which are connected to the ground as well. My Vcc is connected directly to 5V without a capacitor there. Though i do have a decoupling capacitor between vcc and the common ground.

Me

This is very helpfull. Now my module uses 3.3V for VCC. Is this a problem for the RS232 communication voltage levels?

Eminem

MAX232 is used to convert TTL voltage levels into RS232 ones. TTL means 5v and 0v, and my RS232 are -9v and +9v. The MAX232 "flips" and amplifies voltage levels. But im not a big expert, so il suggest you will wait for others to say their opinions.

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