Re: New Driver: parallax

On 11.07.2012 21:59, Jeremy Blow wrote:
> On Jul 11, 2012, at 11:31 AM, Markus Dolze wrote:
>>>
>>
>> Hi,
>>
>> those 'serial' displays are available from a number of companies
>> including Parallax, Sparkfun, and others. They are not really made for
>> PC use but for use with microcontroller boards like Arduino.
>>
>> If one wants to use those with a PC, either a level converter or an
>> USB-to-serial bridge is (usually) needed. Summing up the prices for one
>> of those serial displays and an USB-to-serial bridge is close to a
>> PC-ready display like the Crystalfontz CFA-533. And the latter one has a
>> keypad!
>>
>> On the other hand, if one wants to build a display himself, the LCD2USB
>> is much cheaper to build.
>>
>> For these reasons I am not very confident in using those displays with a
>> PC and I don't own one (yet).
>>
>> Regards,
>> Markus
>>
>
> Hi Markus,
>
> Yup, precisely. I had it in my parts bin for arduino/microcontroller
> stuff. Getting from RS232 to TTL should have been trivial, but my
> circuit to invert and lower the signal just wasn't working correctly.
> I suspect the problem was with the com port, but I didn't have an
> o-scope to verify. Fun hack until I couldn't test any deeper. Been
> thinking about getting that cool little o-scope from those Aussie
> BitScope guys (bitscope.com <http://bitscope.com>), just haven't
> pulled the trigger yet. 
>
> Incidentally, I just received my CFA631 from Crystalfontz in the mail
> today! 
>
> Jeremy
>

Hi,

at first I was surprised about your easy 'level-shifter circuit', but
then I remembered that I had seen this before as the SparkFun RS232
Shifter Board Kit (http://www.sparkfun.com/products/133).

Just out of curiosity I built your circuit like this:

                                            VCC
                                             +
                                             |
                                             |
                                            .-.
                                        10K | |
                                            | |
                                            '-'
                                             |
                                             o---> TX
                                             |
                                   ___     |/
                           TX >---|___|----|  BC547
                                   1K      |>
                                             |
                                             |
                                            ===
                                            GND

Used a BC547 because I had no 2N3904 available. At 9600 baud
communication with my ATmega board was sufficiently reliable.

But after all I still prefer a 'real' level shifter.

Have a nice day!
Markus