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Topic: Increasing arduino UART voltage level (Read 653 times) previous topic - next topic

i3dm

i didnt explain but my board id already made without room for more components. the max232 can easily be mounted on the uart cable though.

MorganS - can you describe the correct way to get the Max232 to output 0-12v (or so) uart? will it also be able to read the LIN bus and transmit TTL (inverted) uart to Ardu?

the max232 i have are the ones from ebay:
https://rover.ebay.com/rover/0/0/0?mpre=https%3A%2F%2Fwww.ebay.com%2Fulk%2Fitm%2F132475473691

theyre actually called MAX3232.

wvmarle

The MAX3232 is the 3.3V version. The MAX232 is the 5V version, and can handle overall higher voltages. Otherwise they're compatible.

The 3232 can handle 10V signals as well, according to the data sheet.
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i3dm

#17
May 23, 2019, 05:57 pm Last Edit: May 23, 2019, 05:59 pm by i3dm
yes. i agree.

so how do i modify it to read / send UART (0 to +12v) instead of RS232 (-12v to +12v)?
simply jumper V- (pin 6) to GND?
which cap needs to be removed?

i3dm

A MAX232 makes a great level shifter for both TX and RX. You could hack it to 0-10V by omitting one capacitor from the recommended circuit and connect V- to ground. But be aware that it reverses the polarity too: a HIGH input gives a low-voltage output.
I have found this scheme of max3232.
do yo umean removing C4 and connecting V- (pin 6 in max3232) to GND?

MorganS

Looks like both C2 and C4 would be unnecessary if you did not need the voltage inverter function.

SoftwareSerial can invert the data. Some of the more advanced Arduinos like the Teensy can do it in hardware but SoftwareSerial will be easier.
"The problem is in the code you didn't post."

i3dm

#20
May 24, 2019, 10:13 am Last Edit: May 24, 2019, 10:20 am by i3dm
Looks like both C2 and C4 would be unnecessary if you did not need the voltage inverter function.

SoftwareSerial can invert the data. Some of the more advanced Arduinos like the Teensy can do it in hardware but SoftwareSerial will be easier.
have you tested the removal of C2 and C4? would love to hear your results.
you also mentioned connecting V- to GND, please elaborate about that.
my main interest is to have a voltage level of 0-12V instead of +-12V from the RS232 side. seems to me like if i remove C2 and C4 i would never get a voltage output at V- at all?
thanks.

i3dm

#21
May 24, 2019, 10:42 am Last Edit: May 24, 2019, 10:43 am by i3dm
I ran a quick test.
removed C2 and C4, V+ rail does show 2*VCC which is to be expected.
than tried inputting TTL and monitoring RS232 output:

"V-" rail not connected: TTL "0" or "1" both show RS232 output 1.3V.
"V-" rail connected to GND: TTL "0" or "1" both show RS232 output 0.5V.

So far the MAX3232 hack is not successful :(

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