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Author Topic: Enhance Parallel Data Transmit with Long Distance Design  (Read 3844 times)

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Offline helpTopic starter

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Enhance Parallel Data Transmit with Long Distance Design
« on: November 03, 2007, 01:13:27 AM »
Hi,

I'm still new on this forum.

I'm trying to transmit 8-bits data from A location to B location which is 20 meters long. Do i need to do any enhancement design on both A and B location so the data can able to transmit more stable condition?

I'm using 8052 MCU. The MCU port will connected it to 74HC573 to pull out the 8-bits data at location-A then transmint the data to location-B (location-B most of that is TTL device, the location-A 8-bits data will link it to 74HC259 and some other logic device. The HC259 output will be connected to x8 LEDs). Between location A and B will be very long distance, 20 Meter. I just plan to use parallel method to transmit the data. I know serial method can solve this problem. I just want to take experience on it. Hope can use parallel method to solve it.

I already did the design but is on testing board. But haven't test it in long distance. 
1) How to solve the transmission line effects?
2) the switching rate is not so frequent. If can turn ON the output LED within 1sec will be nice. Is it possible to do that?
3) driver impedance - using normal TTL driver HC573 (data output driver), HC259(input device), 4077, HC153, HC00 and so on..
5) Normal parallel port 25-pin connector and cable.

What other issue i have to consider? For your experience this design able to achieve? Please advice...

Thank you.
« Last Edit: November 03, 2007, 01:14:04 AM by help »

Offline dunk

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Re: Enhance Parallel Data Transmit with Long Distance Design
« Reply #1 on: November 03, 2007, 07:36:05 AM »
20 meters should be possible with TTL voltages but the higher you make the signal voltage the more reliable your results will be.
if you experience problems @5V consider boosting the voltage of the signal before you send it.
using shielded cable will improve the range a little as well.

dunk.

Offline Tsukubadaisei

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Re: Enhance Parallel Data Transmit with Long Distance Design
« Reply #2 on: November 03, 2007, 09:01:27 AM »
Or use a operational amplifier circuit at the receiving end.
A.I.(yes those are my initials)

Offline dunk

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Re: Enhance Parallel Data Transmit with Long Distance Design
« Reply #3 on: November 03, 2007, 07:06:51 PM »
Quote
Or use a operational amplifier circuit at the receiving end.
the problem with amplifying the received signal is you are also amplifying any noise picked up on the line due to interference.
if you boost the signal before you transmit you get a far better SNR (Signal to Noise Ratio) at the receive end.

RS232 serial comms are typically good for several hundred meters with a voltage difference of 20 to 30V.

dunk.

Offline Tsukubadaisei

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Re: Enhance Parallel Data Transmit with Long Distance Design
« Reply #4 on: November 03, 2007, 08:13:24 PM »
But you can use a band pass filter before connecting the signal to the op-amp and thus "kill" all the noise(make the filter so it will only pass extremelly high or low frequencies). The circuit is very simple and it works.
A.I.(yes those are my initials)

Offline helpTopic starter

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Re: Enhance Parallel Data Transmit with Long Distance Design
« Reply #5 on: November 04, 2007, 01:29:10 AM »
Hi, dunk and Tsukubadaisei,

Thank for you all advice. For the transmiter side we can use 74HC07 Open Drain output for the design. For the Receiver side may be we can use Optocoupler but quite expansive for the design  :-[ May i know is there any 12V logic device in this market? Do we have other option?
There is another way to enhance the design on transmitsion line which is have parallell ground/return wire tight on each data wire to make best possible transmission line with constant impedance.
May be we can design the RC circuit before we transmit out the data? Is there got any improvement?

It seem like very not suitable for this application. But we try to learn something..

Thank You.
« Last Edit: November 04, 2007, 01:50:46 AM by help »

Offline helpTopic starter

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Re: Enhance Parallel Data Transmit with Long Distance Design
« Reply #6 on: December 07, 2007, 09:55:06 PM »
Hi,

Thank for your all advice and shared the knowledge.
 
Last week i just done the testing. It working fine.
I'm using ribbon cable to carry my data along 24 feets and i'm using low-level logic signal as my data signal.
The transmision data rate is around 1Kbps.

I'm not sure that is the long term solution but i'm be observed one week it working very well. Alot of people don't advice to use parallel data for long distance transmission. I will try to switch the design to serial 485.

Thank again...

Offline Admin

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Re: Enhance Parallel Data Transmit with Long Distance Design
« Reply #7 on: December 13, 2007, 02:46:20 PM »
Quote
For the Receiver side may be we can use Optocoupler but quite expansive for the design  Embarrassed May i know is there any 12V logic device in this market? Do we have other option?
What happens with really long cables is that the voltage drops (because of line impedance/resistance). So if you put in 12V input, the output voltage would be lower, depending on the length and resistance of the wire.

the MAX232 uses +/-12V signals for this reason

Offline brijesh

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Re: Enhance Parallel Data Transmit with Long Distance Design
« Reply #8 on: December 14, 2007, 12:02:07 PM »

For a 24 feet long parallel design differential signals like LVDS are the best. For low data throughput, single ended (what you are using now) works fine if you take care of ground lines and termination. As it was mentioned earlier having a ground line close to every signal line helps a lot. With a ribbon cable you alternate ground and signal wires.

For termination if its a point to point link, then source termination will work. In source termination you should put a series resistor at the output of the driver, usually 33 Ohms.







Offline helpTopic starter

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Re: Enhance Parallel Data Transmit with Long Distance Design
« Reply #9 on: December 14, 2007, 11:35:41 PM »
Hi Admin,
Thank for your advice... I though the MAX232 is +5V driver for RS232. I will try to use 12V for my data signal if i got time to modificed it.

Hi brijesh,
Thank for your good infomation. You let me feel more confidence with my design. I had do some study on LVDS http://www.interfacebus.com/Design_Connector_LVDS.html 
I'm not so understand what you have mean.. source termination there put a series resistor. Please give some advice, bellow is my design.

Thank You.
« Last Edit: December 14, 2007, 11:36:24 PM by help »

Offline Admin

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Re: Enhance Parallel Data Transmit with Long Distance Design
« Reply #10 on: December 15, 2007, 10:45:41 AM »
Quote
Thank for your advice... I though the MAX232 is +5V driver for RS232. I will try to use 12V for my data signal if i got time to modificed it.

A little bit more light reading on 232:
http://www.societyofrobots.com/microcontroller_uart.shtml#rs232
http://www.societyofrobots.com/microcontroller_uart.shtml#eia232f
http://www.societyofrobots.com/electronics_negative_voltages.shtml

Offline brijesh

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Re: Enhance Parallel Data Transmit with Long Distance Design
« Reply #11 on: December 16, 2007, 11:36:38 PM »
I found some app notes regarding terminating high speed digital I/O.

http://www.analogzone.com/iot_0919.pdf
http://www.edn.com/archives/1998/021698/04df_04.pdf

Figure 7 in the first document gives example of series termination resistor (Rs).

From looking at your design you have done Parallel termination. The 33 ohms resistor to ground at the receiver is the terminating resistor. The advantage of series termination is it consumes less power than Parallel termination.

Assuming that logic 1 from your driver is 3V, then each resistor is sinking about 3/33 = 0.1A. Is your driver capable of sourcing 100mA?
In all probability the driver is not able to source that much current and may have lower voltage at its output. Do measure what voltage you are getting at the receiver.

If all you are interested is in turning On/off leds once a second, it will work. If its not too much trouble replace 33 Ohm resistor with higher value between 50-100 Ohms. That should reduce the amount of current drawn from the driver.

Are you registering the data at the receiver or using it with a simple buffer?

Brijesh


Offline helpTopic starter

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Re: Enhance Parallel Data Transmit with Long Distance Design
« Reply #12 on: December 20, 2007, 06:01:47 AM »
Hi, Admin
Thank for your information.

Hi, brijesh
Thank for your app note. It is good notes.

Sorry brijesh, previously the resistor 33Ohm connection is wrong. If we connect the 33 ohms resistor to ground at the receiver, we would get very low voltage because we already divider the voltage.

You can see the diagram bellow, i had already modified the diagram. Resistor pull-up at transmiter is 33Ohm and the 10kOhm connected to ground at the receiver. In this case would done Parallel termination. In practical value, the receiver voltage is 4.6V.

If i would like to try the Serial termination how can i connect the resistor? I had study the series termination resistor (Rs). How can i make use of this application connection to my design?

From my diagram, a Master would connected to 5 Slave's. The Master would transmint 13 output data's, and receive 1 input.  Please give some advice for this design..  :)

Thank you.

Offline brijesh

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Re: Enhance Parallel Data Transmit with Long Distance Design
« Reply #13 on: January 08, 2008, 02:17:32 PM »
Sorry didn't check the forums for some days. Your schematic is no longer available to look at.

"Resistor pull-up at transmiter is 33Ohm and the 10kOhm connected to ground at the receiver."
That does not sound right. There is no need for a pull-up resistor at the transmitter. 10KOhm at receiver is way too high to act as terminating resistor.

http://www.analogzone.com/iot_0919.pdf
In the above app note look at Figure 9 and 10. Is that what you are trying to do? In your case you have 5 slave devices instead of 3. If all the slave devices are very close together at the end of cable then use Series termination of figure 9, with Rs = 33ohms. Else use figure 10, with R = 50 to 100 Ohms.

Brijesh

Offline helpTopic starter

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Re: Enhance Parallel Data Transmit with Long Distance Design
« Reply #14 on: January 15, 2008, 11:06:47 PM »
Hi,

Is ok.Very happy that you come back.

Quote
"Resistor pull-up at transmitters is 33Ohm and the 10kOhm connected to ground at the receiver."
That does not sound right. There is no need for a pull-up resistor at the transmitter. 10KOhm at receiver is way too high to act as terminating resistor.

I have already tested, without pull-up resistor on transmiter driver there is no signal when the 7407 input driver is Hi. The value that i select 33Ohm (transmiter pull-up res.) and 10kOhm(receiver res. ground) which is using voltage divider formula to calculate out the resistor value.
I'm not sure, according the transmiter driver is it not suitable for the Parallel Termination design? (Fig8: End Or Parallel Termination)

Quote
http://www.analogzone.com/iot_0919.pdf
In the above app note look at Figure 9 and 10. Is that what you are trying to do?

Ya, from the the diagram Source Termination is show similar with the app note Figure 9.
But i miss put some of the resistors on diagram Source Termination. Please look the Source Termination 2 attached diagram. Is it necessary to put the 33Ohm on each receiver connected to ground?
Quote

In your case you have 5 slave devices instead of 3. If all the slave devices are very close together at the end of cable then use Series termination of figure 9, with Rs = 33ohms. Else use figure 10, with R = 50 to 100 Ohms.

The connection slave between each other is not near. Between the slave distance it was around 6 feetís. What's your advice?

I'm still no decision on choosing Seriaes or Parallel Termination design. I already study the Advantage and Disadvantage for both. Please kindly advice.

Thank You very much..
Best Regard,
Help
« Last Edit: January 15, 2008, 11:08:29 PM by help »

Offline brijesh

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Re: Enhance Parallel Data Transmit with Long Distance Design
« Reply #15 on: January 17, 2008, 11:27:33 PM »
Hello,


Right now I am on vacation in India and net connections sucks big time where I am now.

So can't go into too much details. But here are some pointers.

1) If the slave devices are more than 6 feet apart. Then go with parallel termination.
2) I was not aware you were using open collector driver. For open collector driver you do need that 330Ohm pullup resistor at the transmitter. Have not dealt the open collector drivers before and hence have not thought about termination issues with them. All the termination discussion we have had and the appnotes assume non-open collector drivers. My initial hunch is that termination gets messy with open collector drivers. Is it possible to use normal TTL drivers?

3) If you can use non-open collector driver then a single resistor to ground at the last slave device should work. Use resistor values between 50-100Ohms. Note there should be only one resistor to ground on any given line and it should be at the end of the line(at the last slave device). This is simplest and will work for most of the cases.





 


Offline helpTopic starter

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Re: Enhance Parallel Data Transmit with Long Distance Design
« Reply #16 on: January 19, 2008, 12:23:54 PM »
Hi,

Very good, enjoying your life... :)
From my datasheet book. Most of the TTL IC internal had a pull-up resistor some is ~120Ohm (eg. 74..LS00,LS04,LS10,LS20..SN74LS63 and so on).
I'm tried using open collector is because my initial was using normal TTL (74hc573) IC. After that i changed it to open-collector bcz i plan to use high level signal (+12V) as transmition signal ask our FORUM fren advice (they say low lavel signal is quite unsafe to drive the data for long distance).

If non-open collector TTL driver the 50-100Ohm resistor to ground at the last slave can work mean..the open collector shoould do as well...am i rite?

Thank you pick your time to reply my question. Enjoy your holidays ya...

Bst Rgd..








 


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