dan412
Posts: 6
Joined: Sun Dec 20, 2015 8:12 pm
Location: Brooklyn, NY

MAX232 to TTL Converter Module

Mon Jan 14, 2019 9:55 pm

Hello:

I bought this board to use with my RPi 3 B+ (with raspbian Stretch)in a project scanning CAN BUS signals off my vehicle using OBDII to DB9 cable.

https://smile.amazon.com/dp/B01JYNHNW6/ ... UTF8&psc=1

I have hooked it up on my RPi, powering it with 5v off the GPIO pin, with TX to GPIO15 (RX) and RX to GPIO14TC. The module powers on for like 2 - 3 seconds and shuts off. Is this normal? Do I have to enable the UART in boot config? Do I need to feed signal to the DB9 connector for it to work?

Thanks in advance.

klricks
Posts: 6317
Joined: Sat Jan 12, 2013 3:01 am
Location: Grants Pass, OR, USA
Contact: Website

Re: MAX232 to TTL Converter Module

Mon Jan 14, 2019 10:36 pm

dan412 wrote:
Mon Jan 14, 2019 9:55 pm
Hello:

I bought this board to use with my RPi 3 B+ (with raspbian Stretch)in a project scanning CAN BUS signals off my vehicle using OBDII to DB9 cable.

https://smile.amazon.com/dp/B01JYNHNW6/ ... UTF8&psc=1

I have hooked it up on my RPi, powering it with 5v off the GPIO pin, with TX to GPIO15 (RX) and RX to GPIO14TC. The module powers on for like 2 - 3 seconds and shuts off. Is this normal? Do I have to enable the UART in boot config? Do I need to feed signal to the DB9 connector for it to work?

Thanks in advance.
The module needs to have a Max3232 chip and not Max232
The module needs to be powered with 3V3 not 5V
Unless specified otherwise my response is based on the latest and fully updated Raspbian Stretch w/ Desktop OS.

drgeoff
Posts: 9207
Joined: Wed Jan 25, 2012 6:39 pm

Re: MAX232 to TTL Converter Module

Mon Jan 14, 2019 10:43 pm

klricks wrote:
Mon Jan 14, 2019 10:36 pm
dan412 wrote:
Mon Jan 14, 2019 9:55 pm
Hello:

I bought this board to use with my RPi 3 B+ (with raspbian Stretch)in a project scanning CAN BUS signals off my vehicle using OBDII to DB9 cable.

https://smile.amazon.com/dp/B01JYNHNW6/ ... UTF8&psc=1

I have hooked it up on my RPi, powering it with 5v off the GPIO pin, with TX to GPIO15 (RX) and RX to GPIO14TC. The module powers on for like 2 - 3 seconds and shuts off. Is this normal? Do I have to enable the UART in boot config? Do I need to feed signal to the DB9 connector for it to work?

Thanks in advance.
The module needs to have a Max3232 chip and not Max232
The module needs to be powered with 3V3 not 5V
The module does have a 3232 chip. Yes it does need to be powered from 3.3 volts. Powering it from 5 volts and connecting its Tx output to the RPI's Rx input risks fatal damage to the RPi. RPi GPIOs are not 5 volt tolerant.

Andyroo
Posts: 2592
Joined: Sat Jun 16, 2018 12:49 am
Location: Lincs U.K.

Re: MAX232 to TTL Converter Module

Mon Jan 14, 2019 10:44 pm

I thought canbus was 4 or 5V?

RS/232 is plus or minus 12V with the MAX3232 chip able to have 13.2v as max Vin and looking at http://www.interfacebus.com/CAN-Bus-Des ... tocol.html though it shares the same connector (DB9) the connections are a long way away from RS/232
Need Pi spray - these things are breeding in my house...

dan412
Posts: 6
Joined: Sun Dec 20, 2015 8:12 pm
Location: Brooklyn, NY

Re: MAX232 to TTL Converter Module

Mon Jan 14, 2019 10:59 pm

Thanks all for the feedback. The listing does say "..Easy serial communication with built-in MAX3232". Thankfully, I haven't hooked up the DB9 port yet, so no harm thus far - RPi still working :). I will power the board with 3.3v and do some more testing.

drgeoff
Posts: 9207
Joined: Wed Jan 25, 2012 6:39 pm

Re: MAX232 to TTL Converter Module

Mon Jan 14, 2019 11:41 pm

dan412 wrote:
Mon Jan 14, 2019 10:59 pm
Thankfully, I haven't hooked up the DB9 port yet, so no harm thus far - RPi still working :).
That you had not hooked up the DB9 port is not a reason to feel safe. The spec sheet for the MAX3232 chip shows that its logic side output (which connects to the RPi) can reach at least Vcc-0.6 and Vcc-0.1 volts. When you powered off 5 volts that means a voltage not less than 4.4 could have been applied to the GPIO pin. It is not uncommon for initial damage and symptoms to be confined to the specific GPIO pins that have been electrically abused but for them to subsequently progressively propagate and eventually kill the SoC.

dan412
Posts: 6
Joined: Sun Dec 20, 2015 8:12 pm
Location: Brooklyn, NY

Re: MAX232 to TTL Converter Module

Tue Jan 15, 2019 1:35 am

Good to know; thanks.

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