4 replies to this topic

[pjnowak]

I hooked up my shift register according to this demo. But when I start up the Netduino I noticed that all of my LED's are initially on until I set them.

The project that I am working on needs them to be in they off state. Even during they initial netduino start up. Is there any way I can do this?

[Mario Vernari]

The state of the register's outputs is (almost) unpredictable. If you want to take control over the outputs behavior, you can do that by leveraging the /OE input. Connect that signal to any Netduino output (which is high by default at startup). When the /OE is high, all the register's outputs are totally "opened", as they were "detached" from the circuit. Since no current can flow through that outputs, also no activity on the leds. Finally, when the Netduino program is ready to control the registers, take the /OE low. Cheers

[Zoot]

Good idea, Mario. I think that in addition to your fix, I would use a 10k resistor to tie the /OE line high. The Netduino pin can still take it low to activate the shift register outputs like you say, but the Netduino won't have to source any current to keep the line high when the shift register outputs are off. Just my $.02

[Mario Vernari]

Good idea, Mario.

I think that in addition to your fix, I would use a 10k resistor to tie the /OE line high. The Netduino pin can still take it low to activate the shift register outputs like you say, but the Netduino won't have to source any current to keep the line high when the shift register outputs are off.

Just my $.02

All the Netduino outputs are driven high by a pullup during startup. You can add your own pullup, but it's already embedded into the micro-controller.
Cheers

[koloy]

I currently have an Arduino, mbed, and finally, a Netduino at my disposal for development / hobbyist use.