Extending distance of TTL signal transmission

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liak
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Extending distance of TTL signal transmission

Post by liak » Tue Sep 30, 2008 10:02 am

Dear all,
I have a microcontroller sending out data to another chip over a distance of about 30cm (1ft). The signal seems corrupted after I extend the distance further another few cm. Since I only need a little bit more extension (a few cm) in the transmission distance, is there any simple and cheap method to do this?

Thanks.

Regards,
Liak

Doj
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Location: East Sussex

Post by Doj » Tue Sep 30, 2008 10:46 am

Hello liak,
Several methods can be employed.

1, make sure you have low value(say 1k for instance) pullups on the transmitter and pull downs on the receiver, this will give very sure 0 and 1 signals.

2, use as slow a speed as you can, this will be very important.

3, use screened cable for the data and do not run the cable near ither data or power supply lines.

4, like RS232 use a higher voltage to send the data and then reduce it at the receive end.

5, make sure the power supplies for both receive and transmit are very clean and are not modulated by noise.

6, make sure there is a very good ground signal for the data that starts at the transmit data point and goes to the receive data point, any power supply current flowing down the data ground will corrupt the signal.

Over such a small distance these ideas should be easy to test and get you working.

Good luck.

liak
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Post by liak » Tue Sep 30, 2008 2:45 pm

Dear Doj,
Thanks a lot for the help! :lol:
I didn't expect to get so many suggestions. I will explore the suggestions one by one.

Thanks again.

Regards,
Liak :)

richardb
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Post by richardb » Tue Sep 30, 2008 9:08 pm

I'll put a disclamer here first as i've never tried to connect to an sd card.

looking at this spec i could imagine that the drive strength to the card is a bit weak.
try changing the resistor divider values to 100 and 200 ohms the pic will easily drive that.

infact ideally put the100R at the transmit end and 200R resistors at the sd card end of the cable, this will act as almost ideal impedance matching to the cable.


another thing you can try if your using software spi is to tweak the routine to delay the clock transition more after a data transition.

do you know if its reading writing or both?
Hmmm..

liak
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Post by liak » Wed Oct 01, 2008 2:33 pm

Dear doj and richard,
Thanks for the replies. I have tested the pull-ups. They helped a lot, just did miracle! Thanks. :lol:

:?: Richard, just to clarify. I am not sure if you have misplaced your reply to my other queries on SD card in another thread here. But thanks anyway, I will look into the SD connection again.

Regards,
Liak

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