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# Why does I need to put some resistors in this part? Answered

I don't what is the reason for putting resistors in this part. Does is connected to the VCC of my Bluetooth module? Why 3 resistors? Can someone explain this? Thank you

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## 6 Replies

seandogue (author)2018-03-05

I can't say authoritatively for this specific circuit, BUT...Many circuits use "pull-down resistors" to avoid capacitance loading on I/O. In the absence of such resistance, the I/O port can float to a logic HI state by way of charging like a tiny battery.

I'd recommend that you perform a net search (google, bing, etc) on the term "pull-down resistor" to learn more. If you're interested, also try learning about "pull-up resistors" while you're at it. Understanding each of these concepts is valuable for productive design of I/O and other circuits.

FriedZombie (author)2018-03-05

For a pulldown config it would have a different config, the value of the resistor going to gnd is a bit low for that. So it looks more like a voltage devider to me. But I guess it also works as a pulldown as well

seandogue (author)2018-03-05

the three resistors in series form a pull-down. That it is tapped as it is is another matter, adn is likely some sort of cheap level-shifter. 5 * 2/3 = 3.3

FriedZombie (author)2018-03-05

To have some sort of voltage devider, two risistors instead of 3 would have also worked.

Also not sure why they banged in the three resistors in this case, since the module is 5v tolerant on tx and rx. their isn't a need to it and you can connect it directly.

liquidhandwash (author)2018-03-05

Some of those Bluetooth modules need 3.3v on the TX pin or they malfunction. Its a quite common circuit, but usually it would have a 2k and a 1k.

Hmmm seems i cant add an image at the moment

have a look here

steveastrouk (author)2018-03-05

+1