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bill.french

Member Since 28 Sep 2010
Offline Last Active Oct 16 2012 08:15 PM

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In Topic: Pull Up/Down Resistors, and when to use them?

04 February 2011 - 09:53 PM

Thanks Bill! Thats exactly what I needed!

What about to drive a relay? If I were to go with a pull up resistor, wouldn't I have to switch from a NPN to a PNP? I'm thinking specifically about about the circuit at http://www.arduino.c...ning/relays.pdf

Or am I just over-engineering this, and the arduino relay circuit is fine?

Thank you for your help!

Sorry, not following you - I don't see where a pull up or pull down resistor would come into play. You do need a resistor to the base of the transistor, but that is not a "pull" in either direction. You *might* want to use a pull down to overcome the momentary pull up resistor during boot up.

In Topic: Pull Up/Down Resistors, and when to use them?

04 February 2011 - 07:32 PM

I guess a basic guideline is if you need to read a 0 or 1 reliably, and your circuit has an "open" state, say the reed switch, then you'll want to use a pull up/down resistor, depending on the circumstances. The problem with an open state is that the input will be open to the environment, so any stray charges can make the input go to 0 or 1 unpredictably. In your case, knowing nothing else about your circuit, you can probably get away with a "pull up" resistor instead, which the netduinos have built in and available for activation via software. This will simplify your circuit.

In Topic: Steps to restore an Erased Netduino

03 February 2011 - 01:21 AM

3. (**WARNING.. no turning back after this point.) Using a jumper, Connect the 3V3 power header to the ERASE pin (gold pad directly underneath digital pin 0) for about 2-3 seconds. After doing this, disconnect the Netduino from your PC.

...

5. Run SAM-BA. Select the COM port that your device is connected to. In my case this was COM4. Select AT91SAM7X512-ex from the dropdown.

In case it's helpful:

for step 3, here's a pic of the erase pad on my netduino plus:
Posted Image