I'm trying to use this to convert rs232 levels from my gsm modem to 5v TTL. I was struggling to get it working. So I devised a test to see if I even got any form of communications. My custom Arduino is based on duemilanove design hence it uses ft232rl. I've unplugged my arduino chip. Now I'm just using the ft232rl ttl pins which are connected to max232. I've connected the T1OUT to R1IN. My theory is I can create a loop back so I should get back whatever I send using the terminal within arduino IDE. I've double quaduple checked my connections using sparkfun and various other sites. But nothing happens. Why?

I get 8.5v on pin2 and -7.5 on pin 6 and according to the datasheet thats within spec. I've powered it using 5v. I've decoupled the VCC.

If you could come up with some common pitfalls with this chip, I will be extremely grateful. Btw I don't have a rs232 port on my pc.

enter image description here

  • 2
    \$\begingroup\$ Schematic of your wiring please. \$\endgroup\$
    – Passerby
    Sep 1, 2013 at 9:17
  • 1
    \$\begingroup\$ The MAX232 needs more then just Vcc decoupling caps, IIRC. Do you have the caps for the flying-capacitor voltage converter as well? (1 uF between pins 1&3, 1 uF between pins 4&5, and 1 uF to ground on both pins 2 and 6) \$\endgroup\$ Sep 1, 2013 at 9:36
  • \$\begingroup\$ I didn't have enough 1uf but all the caps I've used are at least 1uf \$\endgroup\$
    – Ageis
    Sep 1, 2013 at 9:58
  • \$\begingroup\$ When you connect the FT232 TTL pins, does the loopback work as you expect? (BTW, the C on V- is connectyed the wrong way round, but that is unlikely to be your problem.) \$\endgroup\$ Sep 1, 2013 at 12:42
  • \$\begingroup\$ Capacitor at pin 6 must be connected the other way round: positive terminal (+) at GND! \$\endgroup\$
    – Curd
    Sep 2, 2013 at 9:16

2 Answers 2


sorry there was two issues with what I was doing. the breadboard wire used on the TX pin was broken. it looked good as new. must of strained it lol. also I connected it to where.the atmega was hence the TX and rx was the wrong. way round. which is how I discovered the breadboard wire was dodgy.


I didn't read your whole question, but two very obvious problems exhibited by the schematic are that neither power nor ground are connected to the chip.

You can see a example of where I used a similar chip in a real product at http://www.embedinc.com/products/rslink2. Go down to the documentation section to see the schematic.


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