Replace normal Resistors, with SMD Resistors, but which one ?

Other Hardware General Electronics
1

Hi there,

Can someone up here, give me an advice for replacing a normal resistor with a SMD-Resistor ?

I need SMD Resistor for these types:

270 Ohms
100 Ohms
10K Ohms

I need a special item on aliexpress :smiley:

I wanna use these SMD-Resistors as a PULLUP for a PUSH-BUTTON.

2

You might use the Arduino internal pullup resistor.

3

yes, I will check this. Maybe this is a good solution :smiley:

4

270 or 100 ohms would be very small values for pullups

2 Likes
5

yes, this ones, I wanted to use as a voltage devider, from 3.3V to 0,9V. Wanna use it for an AnalogRead. But the 10K ones, for an PullUp. But, as @paulpaulson said, I should use the internal pullups :smiley:

6

Post the current schematic.

7

I have no shematic yet. I just tested it out on a breadboard. :smiley:

8

good luck

1 Like
9

Unbenannt1
Unbenannt1655×542 5.13 KB

it is like this. The AnalogRead from the ESP8266 accepts only a maximum Voltage of 1V. Therefore, I hade to devide the voltage :smiley:

10

Please forget my first shematic, look again here...

Unbenannt1
Unbenannt1568×577 4.24 KB

11

Look at the Analog pin of the Wemos D1 ESP8266 module: https://user-images.githubusercontent.com/53401742/71557972-7db54b80-2a13-11ea-9179-e96319fe7f2b.jpg for example values of the voltage divider.

image

You may also notice that this scheme means that the voltage divider goes after the connected device (LDR in your case) .

12

@tolga121
This will work
LDR_d

13

Unbenannt1
Unbenannt1568×577 4.24 KB

  • If you redraw this you will see GPIO15 is shorted to GND.

  • GPIO02 is connected to 3v3

  • 270R/100R voltage divider gives .9v to the LDR/10k voltage divider. :grimacing:

  • .9v / 100R = 9mA thru the 100R resistor.

BTW, you should draw schematics in a more standard way.

14

I see no push button. Is there a coil spring in there? 'cos I wonder if you are winding us up. :wink:

15

SMD resistors come in several different physical sizes. Which size do you need?

1 Like
16

sorry, was working (yes, on sunday).

It should be hand solderable. I think it was 1206 imperial size :slight_smile:

17

And do the original pads have plated through holes or did they rely on the resistor leads for electrical connection to the back side of the board?

1 Like
18

the PCB will be drawn by me, so therefore, i will make some good pads for the 1206 imp size.

19

Anything should work fine. While your voltage divider resistors are of unusually low values, their power dissipation is still quite low (3.3V/370ohm = ~9ma. 9mA through a 270ohm resistor is 0.02W, so even those itty-bitty 1/16W 0402 resistors would be OK.

Note that 1206 resistor PCB footprints are somewhat disappointingly large - bigger than a vertical mount TH resistor :frowning: Flatter, though, and only use one side of the PCB.

1 Like
20

Yes, I guess this would be a problem. It is going to be a two-layer-pcb.