Hi Guys,

I've just tried to connect one of these to my ATTOpilot V3.

I hooked it up like this......

ATTO                                               TTL to RS232

Telm IN -------------------------------------------TX-O

Telm Out------------------------------------------RX-I


                                                       VCC (3.3V input)

The 3.3V is scaled down from 5V like this.

I can't seem to get it to work?

Am I missing something?

Should I connect is differently?

It works great with a FTDI (USB) but I need it to work from a DB9 RS232.

(I want to try it over IP as I have a great little IP to serial converter that I use allot at work)

Thanks in advance!


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Hi Scott!

Do the Tx or Rx LEDs come on?

Can you check that your 3.3V is in fact 3.3V when it is all powered up - I am worried that using a voltage divider to power a device will not give very good results.


Hi Andrew! :)

No the LED's do not light up but I am measuring 3.34V at the Serial to TTL Converter?

The LED's do light up if I run it at 5V (well the TX LED does) but Dean told me that the Telm Pin on ATTO is 3.3V so I don't want to connect it at 5V.

What I don't get is the the Serial to TTL converter should work down to 2.8V?

I have also tried running it at 5V and putting a voltage dividers (same as before) between the TX and RX pins of the ATTO and the converter. Still no luck there either. (I measured 3.4 V on the TX pin when doing this.)

Do you think I should try a better power supply for the converter?

If so can you please point me in the direction of a circuit diagram of something I could make or buy? (5V to 3.3V)

Thanks Andrew




Hi Scott, The short answer is I don't know. I have had trouble with a similar circuit from Sparkfun as it cheated quite a lot - it did not work without both RS232 Tx and Rx lines being connected. Yours is a little different, so it may be better behaved. Were you powering the converter from a voltage divider? Or just using a voltage divider on the signal lines? Certainly I think using a voltage divider to power the converter is a no-no. This (http://www.dimensionengineering.com/products/de-sw033) is one option for converting 5V to 3.3V, but you might be able to get something from Jaycar or Dick Smith or whoever. A 3-terminal linear voltage regulator would be fine if you want to break out the soldering iron - let me know if you want a part number.

Hi Andrew,

Yeah I might rock on down to Jaycar, do you have a part number?


That looks perfect for the job!

It works! ;)

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