What is an appropriate pull-down resistor size? I am using a 1M resistor connected to the gate of a transistor and IO pin of arduino to control a relay. I wanted this so the floating point would be pulled down to ground. This seems to work fine. I also have a 5v signal coming into an analog pin that I'm using as a digital pin. I also have a pull down resistor but ran out of 1M and used a 10K instead. I'm suspecting there is some voltage leaking through the 10k resistor and putting voltage into my ground. Is this possible? This also does something weird when the 5v signal is engaged, my board outputs 6v volts on IO pins and 5v pin. Is this 10K resistor the issue and will a 1M fix it or is it something to do with it being an analog pin?
my board outputs 6v volts on IO pins and 5v pin
Please post a schematic of your project. Include component part numbers and values, especially the power supply(s). A 10K pulldown resistor should not affect the circuit much at all. 6V anywhere on a 5V Arduino is out of spec and can (will) cause damage.
"I am using a 1M resistor connected to the gate of a transistor and IO pin of arduino to control a relay."
What kind of transistor? NPN does not need a pulldown, a floating pin (during reset) can not drive current to turn the NPN on. A N-channel MOSFET only needs a 10K pulldown.
"I'm suspecting there is some voltage leaking through the 10k resistor and putting voltage into my ground. Is this possible? " No.
What board do you have? Arduino IO pins should not be at 6V.
I am using a 1M resistor connected to the gate of a transistor and IO pin of arduino to control a relay. . I wanted this so the floating point would be pulled down to ground.
Transistors don't have a "gate", MOSFETs have a gate and transistors have a base.
Since the output of an Arduino is driven high or low you don't generally need a pull-up or a pull-down. Arduino output pins don't float (input pins do).
In some cases with a MOSFET you might want a pull-down for safety to make sure the MOSFET is off in case it's powered when the Arduino isn't powered, or during boot-up/set-up before the I/O pin is configured as output.
Transistors don't have a "gate", MOSFETs have a gate
Field-effect transistors aren't transistors?
I have a nano. The output voltage doesn't increase to 6v until my 5v signal is engaged. Also when this 5v is engaged, I can disconnect the input voltage from Vin and still have my onboard LED to be on but very dim with around 1.5 on the 5v pin. Noticed my arduino is shot and won't program anymore so somewhere this process destroyed my nano. I have another nano so I'm gonna try it again but without the pull-down resistors. Maybe try a diode to drop my incoming 5V just incase that's what fried my board.
Also when this 5v is engaged, I can disconnect the input voltage from Vin and still have my onboard LED to be on but very dim with around 1.5 on the 5v pin.
Your connecting a 5V supply to Vin?
(Vin requires 7-12V)
Care to share a diagram on how everything is connected or even a picture?
I'm currently at the office so I won't have access to my project (I bike to work) and I am using a regulated 12v through a regulator for my input. The problem is when I apply the 5v signal coming from another board and the regulator is disconnected and my board isn't receiving power through my 12v Vin, it still gets some voltage to turn on the LED with the voltage coming from the input pin.
Ahh, this situation could damage the I/O. Will need to figure out how to power both boards ON/OFF at the same time, or how to isolate the signal(s) when one board is OFF.
I'll have to wait until I get home to test out my good nano to see if I feed a 5v into an IO without a power source and see if that LED comes on. If it doesn't I'll know that my input signal could have damaged my old nano. Will it be safe to put in, say, 4v into an IO pin without powering it on? Never had this issue with my Uno, maybe it's just more robust.
Will it be safe to put in, say, 4v into an IO pin without powering it on? Never had this issue with my Uno, maybe it's just more robust.
When powered off and voltage is applied to a pin, the input protection diode will conduct. The current should be limited to <=1mA, so you should have at minimum a 4.7K resistor connected in series with the input. I would suggest using 10K.
So a 10K resistor won't allow a 5v input to an IO pin turn on my board without a power source? I did not know that applying a voltage to a pin without power connected could do any harm.
" I did not know that applying a voltage to a pin without power connected could do any harm."
Yes, applying voltage to pins that are 0.5V or more above VCC and 0.5V or less below ground can damage the IO pin voltage clamp diodes and actually cause the uC to act as if it was powered up. The diodes are not rated for any current in the spec, but numbers have been found suggesting that the clamp current be limited to < 1ma.
Yes, applying voltage to pins that are 0.5V or more above VCC and 0.5V or less below ground can damage ......
Note this applies to ALL electronics, not just an Arduino.
I feel stupid, but I just realized that when I ordered my nanos they were knock-off ones. 12v is the absolute max that they are rated for so I'm assuming operation for too long at this voltage can cause my ATMEGA to get hot and eventually fail. I'm switching to a 9v regulated input source and hopefully this won't fry out my last "nano".
The '328P won't get hot, but the 5V fixed regulator will. Until the regulator goes bad anyway.
I know this thread is really old, but Crossroads sounds pretty knowledgeable, perhaps an Engineer. So I'd like to ask if the pulldown resistor also serves to bleed down the gate capacitance?
I'm looking to use an Arduino to pulse a transformer. I can use either H Bridge or push pull since I have the parts to build either. I'd prefer push pull if I can minimize dead time in between pulses. If the pulldown resistor bleeds the gate capacitance, then I may not be able to eliminate dead time but I could sure reduce it.
You are responding to a 3 year old thread. Why not start a new one?
Yes, I am an Electrical Engineer.
Yes, pull down resistor will bleed off gate capacitance.