Raspberry Pi Forums

I'm new to the Raspberry Pi, and have come across a couple of projects where there's a resistor across two of the pin and wondered why this would be?

For example, I think the first was a temperature sensor (DHT22/11), where there was a resistor across the data and the gnd connections.

I've seen another project where you interface the Raspberry Pi with trigger pins on an alarm system, and again there's a resistor bridged across the data and gnd connections.

TheBinarySheep wrote:I'm new to the Raspberry Pi, and have come across a couple of projects where there's a resistor across two of the pin and wondered why this would be?
For example, I think the first was a temperature sensor (DHT22/11), where there was a resistor across the data and the gnd connections.
I've seen another project where you interface the Raspberry Pi with trigger pins on an alarm system, and again there's a resistor bridged across the data and gnd connections.

Without any info. from the sensor and/or alarm data sheets my guess would be as a "stronger" pull-down than can be set by programming the SoC appropriately. (IRCC, "programmable" pull-ups/pull-downs are ~50k ohms ... so, what are the resistor values)
Trev.

I honestly think a lot of people just don't know there's a built-in resistor.

Without more details, I'm going with "old habits die hard." I've had to with every other microcontroller because they'd happily pull too much current and fry. Now I've learned I don't generally need to with the Pi, but it still feels weird not to.

ElEscalador wrote:Without more details, I'm going with "old habits die hard." I've had to with every other microcontroller because they'd happily pull too much current and fry. Now I've learned I don't generally need to with the Pi, but it still feels weird not to.

I think you might be mixing up "pull-up" and "pull-down" resistors with "current limit" resistors which are in series with the GPIO pin not in parallel.

PeterO