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Author Topic: Sensitive Board: Protection suggestions?  (Read 3065 times)

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Offline RatfinkTopic starter

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Sensitive Board: Protection suggestions?
« on: April 30, 2007, 07:35:22 AM »
Im working with the following hardware:

www.isep.pw.edu.pl/ZakladNapedu/lab-skp/2812_ezdsp_TechRef_F.pdf

Its input/output pins are very sensitive and any variation in its input output configuration to actual inputs/outputs, voltage levels or any possible short between any pins causes the board to fail (I've managed to do this 3 out of 3 now doh!)

If anyone can suggest any buffers between the pins and its driving input/outputs it would be greatly appreciated.

Voltages the pins work on are 3.3V

Offline nanob0t

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Re: Sensitive Board: Protection suggestions?
« Reply #1 on: April 30, 2007, 11:12:38 AM »
There are little wires for the pins.  I think they are called jumper wires.  You can make these and they're very reliable.  I'll find a picture....

http://www.superdroidrobots.com/images/MCU-012-002.jpg

Take a look at that.  They are "jumper wires".  They consist of a small metal piece that latches onto pins and are soldered onto it.  Then shrink wrap is shrunk around the connection.  I se these for my development board and they are very reliable.  You can either make these or you can buy them cheap.

Offline RatfinkTopic starter

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Re: Sensitive Board: Protection suggestions?
« Reply #2 on: April 30, 2007, 11:49:44 AM »
Hi thanks for your replay we've made these recently and are going to replace them with headers.

but we still have this problem...


Scenario 1:
if the intput/output configuration of the board doesn't match up exactly with what its driving
for example: pin is setup for output and connecting pin is driving an input to this pin
then board is fried.

Scenario 2:
driving the input pin over its maximum 3.3v rating then..
board is fried.

We need someway of effecitvely making sure no matter what pin settings or what we're connecting the board to (e.g. max232 chip, IR range finder, FPGA board) there is a intermediate stage which will protect the board from being fried.

Any suggestions would be welcomed
« Last Edit: April 30, 2007, 03:23:27 PM by Ratfink »

Offline RatfinkTopic starter

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Re: Sensitive Board: Protection suggestions?
« Reply #3 on: April 30, 2007, 03:45:16 PM »
To illustrate my problem further i have included a typical example





http://i12.tinypic.com/66c359k.jpg

Note: The pins on the DSP side are General Purpose Input Output Pins and i want to protect the Expensive thingy incase i make a mistake setting the GPIO to the wrong setting as illustrated.
« Last Edit: April 30, 2007, 03:46:22 PM by Ratfink »

Offline Admin

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Re: Sensitive Board: Protection suggestions?
« Reply #4 on: April 30, 2007, 05:02:04 PM »
what about a diode or buffer IC? :P

Offline dunk

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Re: Sensitive Board: Protection suggestions?
« Reply #5 on: April 30, 2007, 05:24:35 PM »
i've never had to use anything delicate enough to need them but optoisolators are a common choice for this sort of problem.
http://en.wikipedia.org/wiki/Optoisolator

dunk.

Offline RatfinkTopic starter

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Re: Sensitive Board: Protection suggestions?
« Reply #6 on: April 30, 2007, 05:41:02 PM »
The buffer route is what i thought i was going for in the picture i've posted the chip is the following datasheet:

http://www.ortodoxism.ro/datasheets/philips/74lv245.pdf

This would protect the voltage level problem but...

It wouldn't protect it from the one illustrated would it??

Offline dunk

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Re: Sensitive Board: Protection suggestions?
« Reply #7 on: May 01, 2007, 02:43:03 AM »
so the buffer you posted a link to there is a transceiver, meaning it will pass current in either direction.
it will solve your over voltage problem but not the problem of you sending an output pin a signal.

most of us on the forum here are used to dealing with microcontrollers with fairly robust i/o pins but i believe the correct way to connect digital i/o pins is to put a resistor between them.
for example in your diagram, there should be a resistor between ping 16 of your buffer and the DSP.
to find the value of the resistor, look up the DSP datasheet and see if you can find it's I/O pins maximum output current then use I=V/R (from your high school physics class) to find the value of the resistor for that voltage.
this calculation will be presuming that the buffer pin is outputting 0Volts and the DSP pin is at logic 1.
the resistor will dissipate the power between the two pins but should still allow you to make readings when one of the pins is set as an input.

let me know if i'm not making sense.

dunk.

Offline RatfinkTopic starter

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Re: Sensitive Board: Protection suggestions?
« Reply #8 on: May 01, 2007, 04:02:58 AM »
The reason why i need something robust for someone accidentally setting the GPIO pins to the scenario 1 above is we have ALOT of pins i mean atleast 50 or more pins. Its connected to another FPGA and alot of other devices, the person i've inherited the project was kind enough to not include pin diagrams.

So someone or myself may accidentally set the pin to the wrong setting or connect it to the wrong pin leaving us with another fried expensive board (on 4th one now btw  :-[)

I understand what your saying about the maximum power current rating this would work fine for an input but i really need something to protect the board from scenario 1.

Offline dunk

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Re: Sensitive Board: Protection suggestions?
« Reply #9 on: May 01, 2007, 05:55:50 AM »
yup. i was talking about scenario 1.
you mean both connected pins are set to output.
connect the 2 output pins through a resistor.
if the pin on one side of the resistor is set high and the pin on the other side is set low, the resistor converts the power to heat.
you need to pick a resistor that will not allow more than the maximum current to flow. (the max current will be in the datasheets somewhere.)

dunk.

 


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