Simple request about NI 9401

[MarcoMeta]

Hi,

Since I can't reach to ufficial NI support, I hope you can help me with this simple question.

I’ve broken a cRIO module, NI 9401, that we have already sent to repair. Now, I would like to make sure to not destroy it again once it come back. My set up was quite simple: DIO0 to DIO3 configured to read and connected to 4 LEDs driven with PWM signals 0-13V, 100Hz and variable duty cycle from 0 to 100%. DIO4 configured to produce a PWM 0-5V, 1000Hz, 5% duty cycle and connected to an ECU that sample that signal. PIN1 was connected to a common ground while PIN13 was connected to a breadboard with some resistors bridges and transistors used to simulate variable resistances. These components were driven by a voltage produced by other modules (NI 9264 and 9381). The produced voltage/resistance was then connected to proper ECU pins to be sampled.

The possible causes that I identified are the too high voltage of the LEDs PWM signal (12-13V) or a too high current passing through two COM pins that fried the whole module: the damage to the NI 9401 was so severe that there was no pin that could read or produce a proper PWM signal.

Since I’ve already changed the ground connection to the breadboard (bypassing any NI module), what I would like to know is if NI 9401 can withstand 4 PWM signals at 13V or I have to step them down to around 5V. From the datasheet, I read that it can withstand 30V on a single pin, so 13 shouldn't be a big deal.

Thanks in advance.

[santo_13 · Accepted solution]

Looks like you need to reconsider your whole circuit connection.

Could you please share the whole connection diagram and operating voltages to see if anything can be improved?

The pins of 9401 should NOT be exposed beyond 5.25V if you've exposed them to 13V for an extended period on more than one channel, then great! you've fried the module (maybe beyond repair). Of course, the absolute maximum is 30V on a channel, but any prolonged operation of the pins beyond typical conditions will slowly degrade and finally damage it beyond recovery.

Just because your car has an Air Bag you will not crash into a tree to stop it instead you will use the brake always, AirBag is present to be safe from any unavoidable or out-of-control instances. Similarly, these absolute maximum specifications can tolerate a random instance of voltage spike in the signal line but not always high voltage on the line.

Always, abide by the datasheet and do not operate the module in conditions not mentioned in the datasheet.

[MarcoMeta]

Thanks for your answer.

I've added 4 resistor bridges (100K + 44K) to step down the 13V to around 4, so that I can read them safely.