Author Topic: Serial 7 segment LED display, long signal line denoise  (Read 1397 times)

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Offline calliTopic starter

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Serial 7 segment LED display, long signal line denoise
« on: December 16, 2017, 04:02:21 pm »
Hi,

I salvaged this cool device (contains a serial LED 7 segment display) from garbage and have NO clue what it was. But it is cool, I keep it.

However it worked well as I tested it out of its housing, but now with the long cable I suppose I need to denoise the signal lines.

 All what is in the cable is VCC/GND DIN (data), CLK and a Strobe STB directly connected to an Arduinos digital pins. What can I do to denoise the signals?

Thanks,
Carsten
Carsten Wartmann: Make Magazin DE - Autor - Dozent - 3D - Grafik - Maker
http://blenderbuch.de/
 

Offline hlavac

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Re: Serial 7 segment LED display, long signal line denoise
« Reply #1 on: December 17, 2017, 12:18:06 pm »
For long lines you will probably want to go differential signaling over a twisted pair (cat 5cable?).
Look at some RS485 transceivers.
Good enough is the enemy of the best.
 

Offline calliTopic starter

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Re: Serial 7 segment LED display, long signal line denoise
« Reply #2 on: December 17, 2017, 12:20:47 pm »
I assume the device worked for its (unknown) intended purpose with the given cable length. So as the other end of the device is not here, but I think they used some caps/resistors to make the signal more stable... I am looking for advice or even only some google keywords for my own research.

Carsten
Carsten Wartmann: Make Magazin DE - Autor - Dozent - 3D - Grafik - Maker
http://blenderbuch.de/
 

Offline jaycee

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Re: Serial 7 segment LED display, long signal line denoise
« Reply #3 on: December 17, 2017, 06:23:16 pm »
Simple RC filtering would probably do.. as the speed of the signals is likely not very fast, you dont have to worry too much about bandwidth limiting effect. Try something like 100 ohms + 470pF to ground.
 

Offline rstofer

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Re: Serial 7 segment LED display, long signal line denoise
« Reply #4 on: December 17, 2017, 10:12:59 pm »
How long is the 'long' cable?

Is there a possibility that the gadget uses 5V logic and the Arduino uses 3.3V?  What kind of devices are inside the gadget.   Chip numbers...
 

Offline calliTopic starter

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Re: Serial 7 segment LED display, long signal line denoise
« Reply #5 on: December 18, 2017, 08:56:56 am »
The cable is maybe 2 m "long". The Display is a PT6961 based serial 7seq-LED.

The Arduino I used has 5V logic, the PT Chip also.

My 20MHz scope (https://www.eevblog.com/forum/repair/hm205-2-vs-bitscope-dso-look-ma'-no-pixels/msg902679/) is a bit slow to get good readings so I am poking a bit in the dark here...

Carsten
Carsten Wartmann: Make Magazin DE - Autor - Dozent - 3D - Grafik - Maker
http://blenderbuch.de/
 


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